Puglisi, Joseph
Documents Required by the Office of Academic Affairs for Clinician Educator Actions, October 2014 Rank Action Duration Required documents (Number of letters shown are minimums) Clinical Instructor% FTE or greater and who have outside clinical activity, http://med.stanford.edu/academicaffairs/documents
True random numbers from amplified quantum vacuum
M. Jofre; M. Curty; F. Steinlechner; G. Anzolin; J. P. Torres; M. W. Mitchell; V. Pruneri
2011-10-17T23:59:59.000Z
Random numbers are essential for applications ranging from secure communications to numerical simulation and quantitative finance. Algorithms can rapidly produce pseudo-random outcomes, series of numbers that mimic most properties of true random numbers while quantum random number generators (QRNGs) exploit intrinsic quantum randomness to produce true random numbers. Single-photon QRNGs are conceptually simple but produce few random bits per detection. In contrast, vacuum fluctuations are a vast resource for QRNGs: they are broad-band and thus can encode many random bits per second. Direct recording of vacuum fluctuations is possible, but requires shot-noise-limited detectors, at the cost of bandwidth. We demonstrate efficient conversion of vacuum fluctuations to true random bits using optical amplification of vacuum and interferometry. Using commercially-available optical components we demonstrate a QRNG at a bit rate of 1.11 Gbps. The proposed scheme has the potential to be extended to 10 Gbps and even up to 100 Gbps by taking advantage of high speed modulation sources and detectors for optical fiber telecommunication devices.
Quantum Response at Finite Fields and Breakdown of Chern Numbers
@physics.technion.ac.il #12; Quantum Response at Finite Fields and Breakdown of Chern Numbers 2 On closer inspection oneQuantum Response at Finite Fields and Breakdown of Chern Numbers J E Avron and Z Kons y Department singularity at zero field. We also study the breakdown of Chern numbers associated with the response
Spin-statistics-quantum number connection and supersymmetry
Richard M. Weiner
2013-02-05T23:59:59.000Z
The analogy between the Skyrme and Higgs field leads to the conjecture that all fermions are skyrmions and thus always carry conserved quantum numbers, which are identified with baryon or lepton quantum numbers. This connection between spin and quantum numbers, which parallels the connection between spin and statistics due to the Pauli principle, may explain why supersymmetry has not been observed. Creation of s-particles at higher than present energies due to a breakdown of the Skyrme mechanism might imply the violation of the exclusion principle.
High speed optical quantum random number generation
Weinfurter, Harald
.3351 (2009). 6. I. Reidler, Y. Aviad, M. Rosenbluh, and I. Kanter, "Ultrahigh-speed random number generation
Harmonic resolution as a holographic quantum number
Bousso, Raphael
2009-01-01T23:59:59.000Z
LBNL- 57239 Harmonic resolution as a holographic quantumhep-th/0310223 UCB-PTH-03/26 Harmonic resolution as aquantum number, the harmonic resolution K. The Bekenstein
I. Dotsenko; M. Mirrahimi; M. Brune; S. Haroche; J. -M. Raimond; P. Rouchon
2009-05-01T23:59:59.000Z
We propose a quantum feedback scheme for the preparation and protection of photon number states of light trapped in a high-Q microwave cavity. A quantum non-demolition measurement of the cavity field provides information on the photon number distribution. The feedback loop is closed by injecting into the cavity a coherent pulse adjusted to increase the probability of the target photon number. The efficiency and reliability of the closed-loop state stabilization is assessed by quantum Monte-Carlo simulations. We show that, in realistic experimental conditions, Fock states are efficiently produced and protected against decoherence.
Local Availability of mathematics and number scaling: Effects on quantum physics
Paul Benioff
2012-05-01T23:59:59.000Z
Local availability of mathematics and number scaling provide an approach to a coherent theory of physics and mathematics. Local availability of mathematics assigns separate mathematical universes, U_{x}, to each space time point, x. The mathematics available to an observer, O_{x}, at x is contained in U_{x}. Number scaling is based on extending the choice freedom of vector space bases in gauge theories to choice freedom of underlying number systems. Scaling arises in the description, in U_{x}, of mathematical systems in U_{y}. If a_{y} or \\psi_{y} is a number or a quantum state in U_{y}, then the corresponding number or state in U_{x} is r_{y,x}a_{x} or r_{y,x}\\psi_{x}. Here a_{x} and \\psi_{x} are the same number and state in U_{x} as a_{y} and \\psi_{y} are in U_{y}. If y=x+\\hat{\\mu}dx is a neighbor point of x, then the scaling factor is r_{y,x}=\\exp(\\vec{A}(x)\\cdot\\hat{\\mu}dx) where \\vec{A} is a vector field, assumed here to be the gradient of a scalar field. The effects of scaling and local availability of mathematics on quantum theory show that scaling has two components, external and internal. External scaling is shown above for a_{y} and \\psi_{y}. Internal scaling occurs in expressions with integrals or derivatives over space or space time. An example is the replacement of the position expectation value, \\int\\psi^{*}(y)y\\psi(y)dy, by \\int_{x}r_{y,x}\\psi^{*}_{x}(y_{x})y_{x}\\psi_{x}(y_{x})dy_{x}. This is an integral in U_{x}. The good agreement between quantum theory and experiment shows that scaling is negligible in a space region, L, in which experiments and calculations can be done, and results compared. L includes the solar system, but the speed of light limits the size of L to a few light years. Outside of $L$, at cosmological distances, the limits on scaling are not present.
Level repulsion, nuclear chaos, and conserved quantum numbers
Garrett, J.D.
1993-12-01T23:59:59.000Z
A statistical analysis of the distribution of level spacings for states with the same spin and parity is described in which the average spacing is calculated for the total ensemble. Though the resulting distribution of level spacings for states of deformed nuclei with Z = 62 - 75 and A = 155 - 185 is the closest to that of a Poisson distribution yet obtained for nuclear levels, significant deviations are observed for small level spacings. Many, but not all, of the very closely-spaced levels have K-values differing by several units. The analysis of level spacings in {sup 157}Ho indicate that considerable caution should be excerised when drawing conclusions from such an analysis for a single deformed nucleus, since the sizable number of spacings that can be obtained from a few rotational bands are not all independent.
Adam Miranowicz; Sahin K. Ozdemir; Jiri Bajer; Go Yusa; Nobuyuki Imoto; Yoshiro Hirayama; Franco Nori
2014-10-09T23:59:59.000Z
We discuss methods of quantum state tomography for solid-state systems with a large nuclear spin $I=3/2$ in nanometer-scale semiconductors devices based on a quantum well. Due to quadrupolar interactions, the Zeeman levels of these nuclear-spin devices become nonequidistant, forming a controllable four-level quantum system (known as quartit or ququart). The occupation of these levels can be selectively and coherently manipulated by multiphoton transitions using the techniques of nuclear magnetic resonance (NMR) [Yusa et al., Nature (London) 434, 101 (2005)]. These methods are based on an unconventional approach to NMR, where the longitudinal magnetization $M_z$ is directly measured. This is in contrast to the standard NMR experiments and tomographic methods, where the transverse magnetization $M_{xy}$ is detected. The robustness against errors in the measured data is analyzed by using condition numbers. We propose several methods with optimized sets of rotations. The optimization is applied to decrease the number of NMR readouts and to improve the robustness against errors, as quantified by condition numbers. An example of state reconstruction, using Monte Carlo methods, is presented. Tomographic methods for quadrupolar nuclei with higher-spin numbers (including $I=7/2$) are also described.
SAMQUA - Quantum Numbers of Compound Nuclear States for R-Matrix Analyses
Bouland, Olivier; Babut, Richard [Commissariat a l'Energie Atomique - DEN/LEPh - C.E. Cadarache, F-13108 St. Paul-lez-Durance (France); Larson, Nancy M. [Nuclear Data Group, ORNL/Oak Ridge, TN (United States)
2005-05-24T23:59:59.000Z
This paper reports the results of a collaborative effort between CEA of France and the DOE of the United States (in particular between le Laboratoire d'Etudes de Physique de Cadarache and the Nuclear Data Group at Oak Ridge National Laboratory): In preparing input for analyses of differential nuclear data using multilevel multi-channel R-matrix theory, a sometimes daunting and often error-prone task is the generation of quantum-number information for all channels for each compound nuclear state (i.e., for each 'spin group', defined by quantum numbers J{pi}). For many years, the code SAMQUA has been available to users of the R-matrix code SAMMY to assist in preparation of that input; the original SAMQUA code, however, was limited to single-channel spin group information. In this paper, an improved version of the SAMQUA code is described. The new SAMQUA permits inclusion of all open reaction channels in the low-energy interaction between one particle (neutron or charged particle) and a nuclear target, and considerably simplifies the determination of the quantum numbers needed for the definition of the reaction channels. SAMQUA, in addition to its primary function of preparing quantum numbers for the SAMMY input file, also provides the possibility to visualize immediately all open reaction channels. This paper gives two examples of the use of SAMQUA, with emphasis on the notions of reaction channels and penetrability.
Attacks exploiting deviation of mean photon number in quantum key distribution and coin tossing
Shihan Sajeed; Igor Radchenko; Sarah Kaiser; Jean-Philippe Bourgoin; Anna Pappa; Laurent Monat; Matthieu Legre; Vadim Makarov
2015-03-30T23:59:59.000Z
The security of quantum communication using a weak coherent source requires an accurate knowledge of the source's mean photon number. Finite calibration precision or an active manipulation by an attacker may cause the actual emitted photon number to deviate from the known value. We model effects of this deviation on the security of three quantum communication protocols: the Bennett-Brassard 1984 (BB84) quantum key distribution (QKD) protocol without decoy states, Scarani-Acin-Ribordy-Gisin 2004 (SARG04) QKD protocol, and a coin-tossing protocol. For QKD, we model both a strong attack using technology possible in principle, and a realistic attack bounded by today's technology. To maintain the mean photon number in two-way systems, such as plug-and-play and relativistic quantum cryptography schemes, bright pulse energy incoming from the communication channel must be monitored. Implementation of a monitoring detector has largely been ignored so far, except for ID Quantique's commercial QKD system Clavis2. We scrutinize this implementation for security problems, and show that designing a hack-proof pulse-energy-measuring detector is far from trivial. Indeed the first implementation has three serious flaws confirmed experimentally, each of which may be exploited in a cleverly constructed Trojan-horse attack. We discuss requirements for a loophole-free implementation of the monitoring detector.
Min-entropy and quantum key distribution: Nonzero key rates for ''small'' numbers of signals
Bratzik, Sylvia; Mertz, Markus; Kampermann, Hermann; Bruss, Dagmar [Institute for Theoretical Physics III, Heinrich-Heine-Universitaet Duesseldorf, D-40225 Duesseldorf (Germany)
2011-02-15T23:59:59.000Z
We calculate an achievable secret key rate for quantum key distribution with a finite number of signals by evaluating the quantum conditional min-entropy explicitly. The min-entropy for a classical random variable is the negative logarithm of the maximal value in its probability distribution. The quantum conditional min-entropy can be expressed in terms of the guessing probability, which we calculate for d-dimensional systems. We compare these key rates to previous approaches using the von Neumann entropy and find nonzero key rates for a smaller number of signals. Furthermore, we improve the secret key rates by modifying the parameter estimation step. Both improvements taken together lead to nonzero key rates for only 10{sup 4}-10{sup 5} signals. An interesting conclusion can also be drawn from the additivity of the min-entropy and its relation to the guessing probability: for a set of symmetric tensor product states, the optimal minimum-error discrimination (MED) measurement is the optimal MED measurement on each subsystem.
Armand Niederberger; Valerio Scarani; Nicolas Gisin
2005-04-15T23:59:59.000Z
In practical quantum cryptography, the source sometimes produces multi-photon pulses, thus enabling the eavesdropper Eve to perform the powerful photon-number-splitting (PNS) attack. Recently, it was shown by Curty and Lutkenhaus [Phys. Rev. A 69, 042321 (2004)] that the PNS attack is not always the optimal attack when two photons are present: if errors are present in the correlations Alice-Bob and if Eve cannot modify Bob's detection efficiency, Eve gains a larger amount of information using another attack based on a 2->3 cloning machine. In this work, we extend this analysis to all distances Alice-Bob. We identify a new incoherent 2->3 cloning attack which performs better than those described before. Using it, we confirm that, in the presence of errors, Eve's better strategy uses 2->3 cloning attacks instead of the PNS. However, this improvement is very small for the implementations of the Bennett-Brassard 1984 (BB84) protocol. Thus, the existence of these new attacks is conceptually interesting but basically does not change the value of the security parameters of BB84. The main results are valid both for Poissonian and sub-Poissonian sources.
Suzuki, Kosuke, E-mail: kosuzuki@gunma-u.ac.jp; Takubo, Shota; Kato, Tadashi; Yamazoe, Masatoshi; Hoshi, Kazushi; Sakurai, Hiroshi [Department of Electronics and Informatics, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan); Homma, Yoshiya [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, 2145-2 Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki 311-1313 (Japan); Itou, Masayoshi; Sakurai, Yoshiharu [Japan Synchrotron Radiation Research Institute, SPring-8, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan)
2014-08-18T23:59:59.000Z
A spin specific magnetic hysteresis (SSMH) curve and an orbital specific magnetic hysteresis (OSMH) curve are obtained for Fe/Au/Fe/MgO multilayers by magnetic Compton scattering and SQUID magnetometer measurements. The SSMH curve with each contribution of magnetic quantum number |m|?=?0, 1, and 2 states is obtained by decomposition analyses of magnetic Compton profiles. Residual magnetization is observed for the SSMH curve with magnetic quantum number |m|?=?0, 2 and the OSMH curve. Although the SQUID magnetometer measurements do not show perpendicular magnetic anisotropy (PMA) in the present Fe/Au/Fe/MgO multilayer film, the SSMH curve with magnetic quantum number |m|?=?0, 2 and OSMH curve show switching behaviors of PMA.
D. Savran; S. Müller; A. Zilges; M. Babilon; M. W. Ahmed; J. H. Kelley; A. Tonchev; W. Tornow; H. R. Weller; N. Pietralla; J. Li; I. V. Pinayev; Y. K. Wu
2005-01-11T23:59:59.000Z
The 100 % polarized photon beam at the High Intensity gamma-ray Source (HIgS) at Duke University has been used to determine the parity of six dipole excitations between 2.9 and 3.6 MeV in the deformed nuclei 172,174 Yb in photon scattering (g,g') experiments. The measured parities are compared with previous assignments based on the K quantum number that had been assigned in Nuclear Resonance Fluorescence (NRF) experiments by using the Alaga rules. A systematic survey of the relation between gamma-decay branching ratios and parity quantum numbers is given for the rare earth nuclei.
Time irreversibility in the quantum systems with infinite number of particles
Yuping Huo
2013-12-24T23:59:59.000Z
The time irreversible evolution of quantum systems with infinite number of particles (QSINP) was studied within a newly constructed algebraic framework. The QSINP could be described by the quantum infinite lattice field. The *-Algebra R is the set of all dynamic variables of the QSINP, in which a special addition and multiplication operations were defined. The full pure state vector (FPSV) \\rho, the pure state vector {\\rho_f} and the equivalent relations within them are also well defined. The set of all pure state vectors, which are equivalent to the FPSV \\rho, is a Hilbert Space {H_\\rho}, if the addition, the inner product and the norm were defined in it. The set of all linear transformation {N_\\rho} on {H_\\rho} is isomorphic to R, and {{N_\\rho},{H_\\rho}} is the representation of R, associated with \\rho. The *-Algebra R has infinitely many non-equivalent irreducible GNS constructions (representations), associated with different nonequivalent FPSVs respectively. It is proved that, the dynamical motions of the QSINP is totally within the GNS construction associated with the initial pure state vector; However, the time reversal transformation makes the initial FPSV and its corresponding dynamical evolution into another non-equivalent GNS construction. Therefore, within the GNS construction associated with the FPSV, the dynamics of the QSINP is time irreversible. Finally, due to the Liouville operator has real continuous spectrum within the GNS construction, the longtime asymptotic solution of Liouville equation in the GNS construction could be treated by the formal scattering theory. The Master equation with dissipative term was obtained, which is formally irrelevant of the initial state and the corresponding GNS construction. This master equation could be regarded as the evolution equation of the QSINP on R.
F. V. Mendes; R. V. Ramos
2014-08-20T23:59:59.000Z
In a recent paper it has been shown how to create a quantum state related to the prime number sequence using Grover's algorithm. Moreover, its multiqubit entanglement was analyzed. In the present work, we compare the multiqubit entanglement of several quantum sequence states as well we study the feasibility of producing such states using Grover's algorithm.
Yang, Jing; Zhao, Degang, E-mail: dgzhao@red.semi.ac.cn; Jiang, Desheng; Chen, Ping; Zhu, Jianjun; Liu, Zongshun; Le, Lingcong; He, Xiaoguang; Li, Xiaojing [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Wang, Hui; Yang, Hui [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Jahn, Uwe [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5–7, 10117 Berlin (Germany)
2014-09-01T23:59:59.000Z
Cathodoluminescence (CL) characteristics on 30-period InGaN/GaN multiple quantum well (MQW) solar cell structures are investigated, revealing the relationship between optical and structural properties of the MQW structures with a large number of quantum wells. In the bottom MQW layers, a blueshift of CL peak along the growth direction is found and attributed to the decrease of indium content due to the compositional pulling effect. An obvious split of emission peak and a redshift of the main emission energy are found in the top MQW layers when the MQW grows above the critical layer thickness. They are attributed to the segregation of In-rich InGaN clusters rather than the increase of indium content in quantum well layer. The MQW structure is identified to consist of two regions: a strained one in the bottom, where the indium content is gradually decreased, and a partly relaxed one in the top with segregated In-rich InGaN clusters.
Atomic and Molecular Quantum Theory Course Number: C561 13 Theory of Operators: II
Iyengar, Srinivasan S.
Number: C561 (d) Does this make sense? The classical definition of the poten- tial energy is the energy on clearly.) (c) Does this definition make sense? ^A |l is another vector. You could call it |m if you like" product of two vectors is a number. Hence the definition in Eq. (13.1) makes sense. (If these arguments
Pavel Lougovski; Raphael Pooser
2014-04-23T23:59:59.000Z
The majority of Quantum Random Number Generators (QRNG) are designed as converters of a continuous quantum random variable into a discrete classical random bit value. For the resulting random bit sequence to be minimally biased, the conversion process demands an experimenter to fully characterize the underlying quantum system and implement parameter estimation routines. Here we show that conventional approaches to parameter estimation (such as e.g. {\\it Maximum Likelihood Estimation}) used on a finite QRNG data sample without caution may introduce binning bias and lead to overestimation of the randomness of the QRNG output. To bypass these complications, we develop an alternative conversion approach based on the Bayesian statistical inference method. We illustrate our approach using experimental data from a time-of-arrival QRNG and numerically simulated data from a vacuum homodyning QRNG. Side-by-side comparison with the conventional conversion technique shows that our method provides an automatic on-line bias control and naturally bounds the best achievable QRNG bit rate for a given measurement record.
Liu Weitao; Sun Shihai; Liang Linmei; Yuan Jianmin [Department of Physics, College of Science, National University of Defense Technology, Changsha, 410073 (China)
2011-04-15T23:59:59.000Z
Any imperfections in a practical quantum key distribution (QKD) system may be exploited by an eavesdropper to collect information about the key without being discovered. We propose a modified photon-number-splitting attack scheme against QKD systems based on weak laser pulses taking advantage of possible multiphoton pulses. Proof-of-principle experiments are demonstrated. The results show that the eavesdropper can get information about the key generated between the legitimate parties without being detected. Since the equivalent attenuation introduced by the eavesdropper for pulses of different average photon numbers are different, the decoy-state method is effective in fighting against this kind of attack. This has also been proven in our experiments.
Hammock, Bruce D.
fraction in terminal bronchioles and bronchiolarization of the alveolar duct (Plopper et al. 1994a, 1994b of the nitroaromatic 1-nitronapthalene (1-NN). Incomplete combustion of both gasoline and diesel fuel results
Lin Song [State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications, Beijing 100876 (China); School of Mathematics and Computer Science, Fujian Normal University, Fuzhou 350007 (China); Wen Qiaoyan; Gao Fei [State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Zhu Fuchen [National Laboratory for Modern Communications, P.O. Box 810, Chengdu 610041 (China)
2009-05-15T23:59:59.000Z
A collective photon-number-splitting attack strategy is proposed, which combines photon-number-splitting attack with an unambiguous set discrimination of quantum state. Verified by this attack strategy, it is shown that a two-way quantum secure direct communication protocol with qubits is insecure in real circumstance. Finally, we present a possible improved version of this kind of quantum secure direct communication protocol.
Mario Stip?evi?
2014-07-10T23:59:59.000Z
A particularly successful detector blinding attack has been recently demonstrated on various quantum key distribution (QKD) systems, performing for the first time an undetectable and complete recovery of the key. In this paper two original contributions are given to understanding and prevention of this attack.
Kowalevski top in quantum mechanics
Matsuyama, A., E-mail: spamatu@ipc.shizuoka.ac.jp
2013-09-15T23:59:59.000Z
The quantum mechanical Kowalevski top is studied by the direct diagonalization of the Hamiltonian. The spectra show different behaviors depending on the region divided by the bifurcation sets of the classical invariant tori. Some of these spectra are nearly degenerate due to the multiplicity of the invariant tori. The Kowalevski top has several symmetries and symmetry quantum numbers can be assigned to the eigenstates. We have also carried out the semiclassical quantization of the Kowalevski top by the EBK formulation. It is found that the semiclassical spectra are close to the exact values, thus the eigenstates can be also labeled by the integer quantum numbers. The symmetries of the system are shown to have close relations with the semiclassical quantum numbers and the near-degeneracy of the spectra. -- Highlights: •Quantum spectra of the Kowalevski top are calculated. •Semiclassical quantization is carried out by the EBK formulation. •Quantum states are labeled by the semiclassical integer quantum numbers. •Multiplicity of the classical torus makes the spectra nearly degenerate. •Symmetries, quantum numbers and near-degenerate spectra are closely related.
Classification of nonlocal two-qubit gates using Schmidt number
S Balakrishnan; Leona J Felicia; R Sankaranarayanan
2010-03-31T23:59:59.000Z
It is known from Schmidt decomposition that Schmidt number of nonlocal two-qubit quantum gates is 2 or 4. We identify conditions on geometrical points of a gate to have Schmidt number 2. A simple analysis reveals that Schmidt number 2 corresponds to controlled unitary gates with CNOT being the only perfect entangler. Further, it is shown that Schmidt strength and entangling power are maximum only for CNOT in the controlled unitary family.
Classification of nonlocal two-qubit gates using Schmidt number
Balakrishnan, S; Sankaranarayanan, R
2009-01-01T23:59:59.000Z
It is known from Schmidt decomposition that Schmidt number of nonlocal two-qubit quantum gates is 2 or 4. We identify conditions on geometrical points of a gate to have Schmidt number 2. A simple analysis reveals that Schmidt number 2 corresponds to controlled unitary gates with CNOT being the only perfect entangler. Further, it is shown that Schmidt strength and entangling power are maximum only for CNOT in the controlled unitary family.
Topological characterization in extended quantum Ising models
G. Zhang; Z. Song
2015-04-01T23:59:59.000Z
We show that a class of exactly solvable quantum Ising models, including transverse-field Ising model and anisotropic XY model, can be characterized as the loops in a two-dimensional auxiliary space. The transverse-field Ising model corresponds to a circle and the XY model corresponds to an ellipse, while other models yield a Cardioid, Limacon, Hypocycloid, and Lissajous curves, et al.. It is shown that the variation of the ground state energy density, which is a function of the loop, experiences a non-analytical point when the winding number of the corresponding loop changes. The winding number can serve as a topological quantum number of the quantum phases in the extended quantum Ising model, which sheds some light upon the relation between quantum phase transition and the geometrical order parameter characterizing the phase diagram.
Quantum corrections to nonlinear ion acoustic wave with Landau damping
Mukherjee, Abhik; Janaki, M. S. [Saha Institute of Nuclear Physics, Calcutta (India); Bose, Anirban [Serampore College, West Bengal (India)
2014-07-15T23:59:59.000Z
Quantum corrections to nonlinear ion acoustic wave with Landau damping have been computed using Wigner equation approach. The dynamical equation governing the time development of nonlinear ion acoustic wave with semiclassical quantum corrections is shown to have the form of higher KdV equation which has higher order nonlinear terms coming from quantum corrections, with the usual classical and quantum corrected Landau damping integral terms. The conservation of total number of ions is shown from the evolution equation. The decay rate of KdV solitary wave amplitude due to the presence of Landau damping terms has been calculated assuming the Landau damping parameter ?{sub 1}=?(m{sub e}/m{sub i}) to be of the same order of the quantum parameter Q=?{sup 2}/(24m{sup 2}c{sub s}{sup 2}L{sup 2}). The amplitude is shown to decay very slowly with time as determined by the quantum factor Q.
Spectrum of surface plasmons excited by spontaneous quantum dot transitions
Andrianov, E. S., E-mail: andrianov.es@mipt.ru; Pukhov, A. A., E-mail: pukhov@mail.ru; Dorofeenko, A. V.; Vinogradov, A. P. [Russian Academy of Sciences, Institute of Theoretical and Applied Electrodynamics (Russian Federation)] [Russian Academy of Sciences, Institute of Theoretical and Applied Electrodynamics (Russian Federation); Lisyansky, A. A. [Queens College of the City University of New York, Department of Physics (United States)] [Queens College of the City University of New York, Department of Physics (United States)
2013-08-15T23:59:59.000Z
We consider quantum fluctuations of near fields of a quantum emitter (two-level system (TLS) with population inversion sustained by incoherent pumping) in the near-field zone of a plasmon (metallic) nanoparticle. The spectrum of surface plasmons excited by spontaneous transitions in the quantum emitter is obtained below the lasing threshold of such a system (spaser) in the approximation of a small number of plasmons. It is shown that the relaxation rate is the sum of the quantum emitter's rates of relaxation to its thermal reservoir and the plasmon cavity. The resulting dependence of the average number of plasmons on the pump intensity indicates the nonthreshold nature of the process.
Quantum digital-to-analog conversion algorithm using decoherence
Akira SaiToh
2014-12-28T23:59:59.000Z
We consider the problem of mapping digital data encoded on a quantum register to analog amplitudes in parallel. It is shown to be unlikely that a fully unitary polynomial-time quantum algorithm exists for this problem; NP becomes a subset of BQP if it exists. In the practical point of view, we propose a nonunitary linear-time algorithm using quantum decoherence. It tacitly uses an exponentially large physical resource, which is typically a huge number of identical molecules. Quantumness of correlation appearing in the process of the algorithm is also discussed.
Single-Shot Quantum Process Tomography
Abhishek Shukla; T. S. Mahesh
2014-05-27T23:59:59.000Z
The standard procedure for quantum process tomography (QPT) involves applying the quantum process on a system initialized in each of a complete set of orthonormal states. The corresponding outputs are then characterized by quantum state tomography (QST), which itself requires the measurement of non-commuting observables realized by independent experiments on identically prepared system states. Thus QPT procedure demands a number of independent measurements, and moreover, this number increases rapidly with the size of the system. However, the total number of independent measurements can be greatly reduced with the availability of ancilla qubits. Ancilla assisted process tomography (AAPT) has earlier been shown to require a single QST of system-ancilla space. Ancilla assisted quantum state tomography (AAQST) has also been shown to perform QST in a single measurement. Here we combine AAPT with AAQST to realize a `single-shot QPT' (SSPT), a procedure to characterize a general quantum process in a single collective measurement of a set of commuting observables. We demonstrate experimental SSPT by characterizing several single-qubit processes using a three-qubit NMR quantum register. Furthermore, using the SSPT procedure we experimentally characterize the twirling process and compare the results with theory.
241 Strength in numbers 243 Great leap outwards
Loss, Daniel
INSIGHT QUANTUM MECHANICS EDITORIAL 241 Strength in numbers THESIS 243 Great leap outwards Mark spintronics: Pumping spins through polymers Bert Koopmans INSIGHT: FOUNDATIONS OF QUANTUM MECHANICS EDITORIAL 253 Foundations of quantum mechanics COMMENTARY 254 Gravity in quantum mechanics Giovanni Amelino
A Simplified Hierarchical Dynamic Quantum Secret Sharing Protocol with Added Features
Sandeep Mishra; Chitra Shukla; Anirban Pathak; R. Srikanth; Anu Venugopalan
2014-09-06T23:59:59.000Z
Generalizing the notion of dynamic quantum secret sharing (DQSS), a simplified protocol for hierarchical dynamic quantum secret sharing (HDQSS) is proposed and it is shown that the protocol can be implemented using any existing protocol of quantum key distribution, quantum key agreement or secure direct quantum communication. The security of this proposed protocol against eavesdropping and collusion attacks is discussed with specific attention towards the issues related to the composability of the subprotocols that constitute the proposed protocol. The security and qubit efficiency of the proposed protocol is also compared with that of other existing protocols of DQSS. Further, it is shown that it is possible to design a semi-quantum protocol of HDQSS and in principle, the protocols of HDQSS can be implemented using any quantum state. It is also noted that the completely orthogonal-state-based realization of HDQSS protocol is possible and that HDQSS can be experimentally realized using a large number of alternative approaches.
Quantum measure and integration theory
Stan Gudder
2009-09-11T23:59:59.000Z
This article begins with a review of quantum measure spaces. Quantum forms and indefinite inner-product spaces are then discussed. The main part of the paper introduces a quantum integral and derives some of its properties. The quantum integral's form for simple functions is characterized and it is shown that the quantum integral generalizes the Lebesgue integral. A bounded, monotone convergence theorem for quantum integrals is obtained and it is shown that a Radon-Nikodym type theorem does not hold for quantum measures. As an example, a quantum-Lebesgue integral on the real line is considered.
Multispecies weighted Hurwitz numbers
Harnad, J
2015-01-01T23:59:59.000Z
The construction of hypergeometric 2D Toda $\\tau$-functions as generating functions for weighted Hurwitz numbers is extended to multispecies families. Both the enumerative geometrical significance of multispecies weighted Hurwitz numbers as weighted enumerations of branched coverings of the Riemann sphere and their combinatorial significance in terms of weighted paths in the Cayley graph of $S_n$ are derived. The particular case of multispecies quantum weighted Hurwitz numbers is studied in detail.
Ginley, D. S.
2010-07-01T23:59:59.000Z
The NREL/Evident team will develop techniques to fabricate thin film solar cells where the absorption layers comprising the solar cells are derived from sintered semiconductor quantum dots.
Reginald T. Cahill
2005-06-06T23:59:59.000Z
In 1990 Alcubierre, within the General Relativity model for space-time, proposed a scenario for `warp drive' faster than light travel, in which objects would achieve such speeds by actually being stationary within a bubble of space which itself was moving through space, the idea being that the speed of the bubble was not itself limited by the speed of light. However that scenario required exotic matter to stabilise the boundary of the bubble. Here that proposal is re-examined within the context of the new modelling of space in which space is a quantum system, viz a quantum foam, with on-going classicalisation. This model has lead to the resolution of a number of longstanding problems, including a dynamical explanation for the so-called `dark matter' effect. It has also given the first evidence of quantum gravity effects, as experimental data has shown that a new dimensionless constant characterising the self-interaction of space is the fine structure constant. The studies here begin the task of examining to what extent the new spatial self-interaction dynamics can play a role in stabilising the boundary without exotic matter, and whether the boundary stabilisation dynamics can be engineered; this would amount to quantum gravity engineering.
Deutsch's Universal Quantum Turing Machine (Revisited)
Willem Fouché; Johannes Heidema; Glyn Jones; Petrus H. Potgieter
2007-01-16T23:59:59.000Z
Deutsch, Feynman, and Manin viewed quantum computing as a kind of universal physical simulation procedure. Much of the writing about quantum Turing machines has shown how these machines can simulate an arbitrary unitary transformation on a finite number of qubits. This interesting problem has been addressed most famously in a paper by Deutsch, and later by Bernstein and Vazirani. Quantum Turing machines form a class closely related to deterministic and probabilistic Turing machines and one might hope to find a universal machine in this class. A universal machine is the basis of a notion of programmability. The extent to which universality has in fact been established by the pioneers in the field is examined and a key notion in theoretical computer science (universality) is scrutinised. In a forthcoming paper, the authors will also consider universality in the quantum gate model.
Convection in Arc Weld Pools Electromagnetic and surface tension forces are shown to
Eagar, Thomas W.
Convection in Arc Weld Pools Electromagnetic and surface tension forces are shown to dominate flow tension forces. It is shown that the electromag- netic and surface tension forces domi- nate the flow by experimental measurements of segrega- tion in the weld pool. It is also shown that the surface tension driven
The quantum field theory interpretation of quantum mechanics
Alberto C. de la Torre
2015-03-02T23:59:59.000Z
It is shown that adopting the \\emph{Quantum Field} ---extended entity in space-time build by dynamic appearance propagation and annihilation of virtual particles--- as the primary ontology the astonishing features of quantum mechanics can be rendered intuitive. This interpretation of quantum mechanics follows from the formalism of the most successful theory in physics: quantum field theory.
Numerical study of ion acoustic shock waves in dense quantum plasma
Hanif, M.; Mirza, Arshad M. [Theoretical Plasma Physics Group, Department of Physics, Quaid-e-Azam University, Islamabad 45320 (Pakistan)] [Theoretical Plasma Physics Group, Department of Physics, Quaid-e-Azam University, Islamabad 45320 (Pakistan); Ali, S.; Mukhtar, Q., E-mail: qaisarm@ncp.edu.pk [National Center for Physics, Quaid-e-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan)
2014-03-15T23:59:59.000Z
Two fluid quantum hydrodynamic equations are solved numerically to investigate the propagation characteristics of ion acoustic shock waves in an unmagnetized dense quantum plasma, whose constituents are the electrons and ions. For this purpose, we employ the standard finite difference Lax Wendroff and relaxation methods, to examine the quantum effects on the profiles of shock potential, the electron/ion number densities, and velocity even for quantum parameter at H?=?2. The effects of the latter vanish in a weakly non-linear limit while obeying the KdV theory. It is shown that the evolution of the wave depends sensitively on the plasma density and the quantum parameter. Numerical results reveal that the kinks or oscillations are pronounced for large values of quantum parameter, especially at H?=?2. Our results should be important to understand the shock wave excitations in dense quantum plasmas, white dwarfs, neutron stars, etc.
NMR quantum information processing
Dawei Lu; Aharon Brodutch; Jihyun Park; Hemant Katiyar; Tomas Jochym-O'Connor; Raymond Laflamme
2015-01-07T23:59:59.000Z
Quantum computing exploits fundamentally new models of computation based on quantum mechanical properties instead of classical physics, and it is believed that quantum computers are able to dramatically improve computational power for particular tasks. At present, nuclear magnetic resonance (NMR) has been one of the most successful platforms amongst all current implementations. It has demonstrated universal controls on the largest number of qubits, and many advanced techniques developed in NMR have been adopted to other quantum systems successfully. In this review, we show how NMR quantum processors can satisfy the general requirements of a quantum computer, and describe advanced techniques developed towards this target. Additionally, we review some recent NMR quantum processor experiments. These experiments include benchmarking protocols, quantum error correction, demonstrations of algorithms exploiting quantum properties, exploring the foundations of quantum mechanics, and quantum simulations. Finally we summarize the concepts and comment on future prospects.
Quantum mechanical time contradicts the uncertainty principle
Hitoshi Kitada
1999-11-17T23:59:59.000Z
The a priori time in conventional quantum mechanics is shown to contradict the uncertainty principle. A possible solution is given.
Quantum corrections to conductivity for semiconductors with various structures
S. A. Alavi; A. Tatar
2011-04-05T23:59:59.000Z
We study the magnetic field dependences of the conductivity in heavily doped, strongly disordered 2D quantum well structures within wide conductivity and temperature ranges. We show that the exact analytical expression derived in our previous paper [1], is in better agreement than the existing equation i.e. Hikami(et.al.,) expression [2,3], with the experimental data even in low magnetic field for which the diffusion approximation is valid. On the other hand from theoretical point of view we observe that our equation is also rich because it establishes a strong relationship between quantum corrections to the conductivity and the quantum symmetry su_{q}(2). It is shown that the quantum corrections to the conductivity is the trace of Green function made by a generator of su_{q}(2)algebra. Using this fact we show that the quantum corrections to the conductivity can be expressed as a sum of an infinite number of Feynman diagrams.
Entropy of Quantum Fields in de Sitter Space-time
M. V. Takook
2014-08-15T23:59:59.000Z
The quantum states or Hilbert spaces for the quantum field theory in de Sitter space-time are studied on ambient space formalism. In this formalism, the quantum states are only depended $(1)$ on the topological character of the de Sitter space-time, {\\it i.e.} $\\R \\times S^3$, and $(2)$ on the homogeneous spaces which are used for construction of the unitary irreducible representation of de Sitter group. A compact homogeneous space is chosen in this paper. The unique feature of this homogeneous space is that its total number of quantum states, ${\\cal N}$, is finite although the Hilbert space has infinite dimensions. It is shown that ${\\cal N}$ is a continuous function of the Hubble constant $H$ and the eigenvalue of the Casimir operators of de Sitter group. The entropy of the quantum fields on this Hilbert space have been calculated which is finite and invariant for all inertial observers on the de Sitter hyperboloid.
Fractal states in quantum information processing
Gregg Jaeger
2007-08-01T23:59:59.000Z
The fractal character of some quantum properties has been shown for systems described by continuous variables. Here, a definition of quantum fractal states is given that suits the discrete systems used in quantum information processing, including quantum coding and quantum computing. Several important examples are provided.
On Conformal Field Theory and Number Theory
Huang, An
2011-01-01T23:59:59.000Z
Frontiers in Number Theory, Physics, and Ge- ometry II. (Witten, Quantum Field Theory, Crassmannians, and AlgebraicJ. Polchinski, String Theory, Vol. 1, Cambridge Univ.
Quantum Bootstrapping via Compressed Quantum Hamiltonian Learning
Nathan Wiebe; Christopher Granade; David G. Cory
2015-03-30T23:59:59.000Z
Recent work has shown that quantum simulation is a valuable tool for learning empirical models for quantum systems. We build upon these results by showing that a small quantum simulators can be used to characterize and learn control models for larger devices for wide classes of physically realistic Hamiltonians. This leads to a new application for small quantum computers: characterizing and controlling larger quantum computers. Our protocol achieves this by using Bayesian inference in concert with Lieb-Robinson bounds and interactive quantum learning methods to achieve compressed simulations for characterization. Whereas Fisher information analysis shows that current methods which employ short-time evolution are suboptimal, interactive quantum learning allows us to overcome this limitation. We illustrate the efficiency of our bootstrapping protocol by showing numerically that an 8-qubit Ising model simulator can be used to calibrate and control a 50 qubit Ising simulator while using only about 750 kilobits of experimental data.
Pierre Bérard; Bernard Helffer
2014-09-08T23:59:59.000Z
In the case of the sphere and the square, Antonie Stern (1925) claimed in her PhD thesis the existence of an infinite sequence of eigenvalues whose corresponding eigenspaces contain an eigenfunction with two nodal domains. These two statements were given complete proofs respectively by Hans Lewy in 1977, and the authors in 2014 (see also Gauthier-Shalom--Przybytkowski (2006)). The aim of this paper is to obtain a similar result in the case of the isotropic quantum harmonic oscillator in the two dimensional case.
Hayashi, A.; Hashimoto, T.; Horibe, M. [Department of Applied Physics, Fukui University, Fukui 910-8507 (Japan)
2005-01-01T23:59:59.000Z
The quantum color coding scheme proposed by Korff and Kempe [e-print quant-ph/0405086] is easily extended so that the color coding quantum system is allowed to be entangled with an extra auxiliary quantum system. It is shown that in the extended scheme we need only {approx}2{radical}(N) quantum colors to order N objects in large N limit, whereas {approx}N/e quantum colors are required in the original nonextended version. The maximum success probability has asymptotics expressed by the Tracy-Widom distribution of the largest eigenvalue of a random Gaussian unitary ensemble (GUE) matrix.
Ari Mizel
2003-12-09T23:59:59.000Z
Ground-state quantum computers mimic quantum mechanical time evolution within the amplitudes of a time-independent quantum state. We explore the principles that constrain this mimicking. A no-cloning argument is found to impose strong restrictions. It is shown, however, that there is flexibility that can be exploited using quantum teleportation methods to improve ground-state quantum computer design.
Colle, C; Cosyn, W; Korover, I; Piasetzky, E; Ryckebusch, J; Weinstein, L B
2015-01-01T23:59:59.000Z
The nuclear mass dependence of the number of short-range correlated (SRC) proton-proton (pp) and proton-neutron (pn) pairs in nuclei is a sensitive probe of the dynamics of short-range pairs in the ground state of atomic nuclei. This work presents an analysis of electroinduced single-proton and two-proton knockout measurements off 12C, 27Al, 56Fe, and 208Pb in kinematics dominated by scattering off SRC pairs. The nuclear mass dependence of the observed A(e,e'pp)/12C(e,e'pp) cross-section ratios and the extracted number of pp- and pn-SRC pairs are much softer than the mass dependence of the total number of possible pairs. This is in agreement with a physical picture of SRC affecting predominantly nucleon-nucleon pairs in a nodeless relative-S state of the mean-field basis.
Wladyslaw A. Majewski; Marcin Marciniak
2005-10-28T23:59:59.000Z
It was shown that quantum analysis constitutes the proper analytic basis for quantization of Lyapunov exponents in the Heisenberg picture. Differences among various quantizations of Lyapunov exponents are clarified.
1. INTRODUCTION Polycrystalline CdTe thin films solar cells have shown long
Romeo, Alessandro
for the solar cell, therefore high specific power (ratio of out- put power to the weight) solar cells]. The high specific power is an important issue for space solar cells: if satellites are lighter1. INTRODUCTION Polycrystalline CdTe thin films solar cells have shown long term stable performance
Paris-Sud XI, Université de
Abstract: Full sequential equivalence checking by state space traversal has been shown, Simulation, SAT) to transform the sequential equivalence checking problem into a combinational equivalence successful in general, they are not able to reach proof of equivalence in presence of complex transformations
Wisconsin at Madison, University of
Printed by Previous studies have shown that positive affect has numerous health benefits in Western is equally beneficial for health across different cultural contexts. Particularly, in East Asian culture in isolation from social relationships may not be beneficial or even harmful for one's health. (Miyamoto
VARIABILITY OF NEARSURFACE ZOOPLANKTON OFF SOUTHERN CALIFORNIA, AS SHOWN BY TOWED-PUMP SAMPLING
VARIABILITY OF NEARÂ·SURFACE ZOOPLANKTON OFF SOUTHERN CALIFORNIA, AS SHOWN BY TOWED-PUMP SAMPLING Cl of 1962. Samples were collected with a towed pump at a depth of 5 m. Allproximately 162 samples, each repl pump surveys re- llorted here were undertaken to obtain informa- tion on variability and trends
Liu, K. J. Ray
problem that seller prosumers actually supply insufficient energy Simulation results have shown user cooperation [18], [19]. Among them, a seller prosumer in a trade is likely to have insufficient sufficient energy to the buyer as it has owners, the autonomous prosumers are assumed to be selfish levels
Elastomeric behavior of exfoliated graphite, as shown by instrumented indentation testing
Chung, Deborah D.L.
Elastomeric behavior of exfoliated graphite, as shown by instrumented indentation testing Po for the first time the elastomeric behavior of a non-polymeric material, as observed in exfoliated graphite sliding of the graphite layers within the cell wall of exfoliated graphite. The reversibility is probably
Several studies have shown that the availability of solar power plants often is
Perez, Richard R.
Several studies have shown that the availability of solar power plants often is high during times conditioning. These peaks are intensi- fied during heat waves, which are fueled by solar gain. Thus the utility, solar and research industries. Effective Capacity Metrics Simple metrics can be estimated
CARDIAC SURGERY MORTALITY RATES UK cardiac surgeons have shown the best way to
Aickelin, Uwe
measure of clinical outcome is at the level of the individual surgeon. That degree of granularity for Cardiothoracic Surgery in Great Britain and Ireland and the National Institute for Clinical Outcomes ResearchCARDIAC SURGERY MORTALITY RATES UK cardiac surgeons have shown the best way to ensure good clinical
Quantum Ice : a quantum Monte Carlo study
Nic Shannon; Olga Sikora; Frank Pollmann; Karlo Penc; Peter Fulde
2011-12-13T23:59:59.000Z
Ice states, in which frustrated interactions lead to a macroscopic ground-state degeneracy, occur in water ice, in problems of frustrated charge order on the pyrochlore lattice, and in the family of rare-earth magnets collectively known as spin ice. Of particular interest at the moment are "quantum spin ice" materials, where large quantum fluctuations may permit tunnelling between a macroscopic number of different classical ground states. Here we use zero-temperature quantum Monte Carlo simulations to show how such tunnelling can lift the degeneracy of a spin or charge ice, stabilising a unique "quantum ice" ground state --- a quantum liquid with excitations described by the Maxwell action of 3+1-dimensional quantum electrodynamics. We further identify a competing ordered "squiggle" state, and show how both squiggle and quantum ice states might be distinguished in neutron scattering experiments on a spin ice material.
Long-range surface plasmon polariton excitation at the quantum level
D. Ballester; M. S. Tame; C. Lee; J. Lee; M. S. Kim
2009-06-02T23:59:59.000Z
We provide the quantum mechanical description of the excitation of long-range surface plasmon polaritons (LRSPPs) on thin metallic strips. The excitation process consists of an attenuated-reflection setup, where efficient photon-to-LRSPP wavepacket-transfer is shown to be achievable. For calculating the coupling, we derive the first quantization of LRSPPs in the polaritonic regime. We study quantum statistics during propagation and characterize the performance of photon-to-LRSPP quantum state transfer for single-photons, photon-number states and photonic coherent superposition states.
Efficiency in Quantum Key Distribution Protocols with Entangled Gaussian States
C. Rodó; O. Romero-Isart; K. Eckert; A. Sanpera
2007-03-21T23:59:59.000Z
Quantum key distribution (QKD) refers to specific quantum strategies which permit the secure distribution of a secret key between two parties that wish to communicate secretly. Quantum cryptography has proven unconditionally secure in ideal scenarios and has been successfully implemented using quantum states with finite (discrete) as well as infinite (continuous) degrees of freedom. Here, we analyze the efficiency of QKD protocols that use as a resource entangled gaussian states and gaussian operations only. In this framework, it has already been shown that QKD is possible (M. Navascu\\'es et al. Phys. Rev. Lett. 94, 010502 (2005)) but the issue of its efficiency has not been considered. We propose a figure of merit (the efficiency $E$) to quantify the number of classical correlated bits that can be used to distill a key from a sample of $N$ entangled states. We relate the efficiency of the protocol to the entanglement and purity of the states shared between the parties.
The propagation of waves in Einstein's unified field theory as shown by two exact solutions
Salvatore Antoci
2009-09-29T23:59:59.000Z
The propagation of waves in two space dimensions exhibited by two exact solutions to the field equations of Einstein's unified field theory is investigated under the assumption that the metric s_{ik} is the one already chosen by Kursunoglu and by H\\'ely in the years 1952-1954. It is shown that, for both exact solutions, with this choice of the metric the propagation of the waves occurs in the wave zone with the fundamental velocity (ds^2=0).
Michael Ben-Or; Daniel Gottesman; Avinatan Hassidim
2013-01-09T23:59:59.000Z
We consider fault-tolerant quantum computation in the context where there are no fresh ancilla qubits available during the computation, and where the noise is due to a general quantum channel. We show that there are three classes of noisy channels: In the first, typified by the depolarizing channel, computation is only possible for a logarithmic time. In the second class, of which the dephasing channel is an example, computation is possible for polynomial time. The amplitude damping channel is an example of the third class, and for this class of channels, it is possible to compute for an exponential time in the number of qubits available.
installed solar electric systems on a number of the city's buildings, including the Chicago Center for Green Technology shown here. CityofChicago Aggregated Purchasing--A Clean Energy Strategy SOLAR TODAY Aggregated Purchasing--A Clean Energy Strategy by Lori A. Bird and Edward A. Holt #12;November/December 2002 35 Power
Quantum Equivalence and Quantum Signatures in Heat Engines
Raam Uzdin; Amikam Levy; Ronnie Kosloff
2015-04-15T23:59:59.000Z
Quantum heat engines (QHE) are thermal machines where the working substance is quantum. In the extreme case the working medium can be a single particle or a few level quantum system. The study of QHE has shown a remarkable similarity with the standard thermodynamical models, thus raising the issue what is quantum in quantum thermodynamics. Our main result is thermodynamical equivalence of all engine type in the quantum regime of small action. They have the same power, the same heat, the same efficiency, and they even have the same relaxation rates and relaxation modes. Furthermore, it is shown that QHE have quantum-thermodynamic signature, i.e thermodynamic measurements can confirm the presence of quantum coherence in the device. The coherent work extraction mechanism enables power outputs that greatly exceed the power of stochastic (dephased) engines.
Device Independent Random Number Generation
Mataj Pivoluska; Martin Plesch
2015-02-23T23:59:59.000Z
Randomness is an invaluable resource in today's life with a broad use reaching from numerical simulations through randomized algorithms to cryptography. However, on the classical level no true randomness is available and even the use of simple quantum devices in a prepare-measure setting suffers from lack of stability and controllability. This gave rise to a group of quantum protocols that provide randomness certified by classical statistical tests -- Device Independent Quantum Random Number Generators. In this paper we review the most relevant results in this field, which allow the production of almost perfect randomness with help of quantum devices, supplemented with an arbitrary weak source of additional randomness. This is in fact the best one could hope for to achieve, as with no starting randomness (corresponding to no free will in a different concept) even a quantum world would have a fully deterministic description.
Hierarchical quantum communication
Chitra Shukla; Anirban Pathak
2013-01-03T23:59:59.000Z
A general approach to study the hierarchical quantum information splitting (HQIS) is proposed and the same is used to systematically investigate the possibility of realizing HQIS using different classes of 4-qubit entangled states that are not connected by SLOCC. Explicit examples of HQIS using 4-qubit cluster state and 4-qubit |\\Omega> state are provided. Further, the proposed HQIS scheme is generalized to introduce two new aspects of hierarchical quantum communication. To be precise, schemes of probabilistic hierarchical quantum information splitting and hierarchical quantum secret sharing are obtained by modifying the proposed HQIS scheme. A number of practical situations where hierarchical quantum communication would be of use are also presented.
Anirban Pathak
2014-11-24T23:59:59.000Z
Recently, Hassanpour and Houshmand have proposed a protocol of controlled deterministic secure quantum communication (Quant. Info. Process, DOI 10.1007/s11128-014-0866-z (2014)). The authors compared the efficiency of their protocol with that of two other existing protocols and claimed that their protocol is efficient. Here, we have shown that the efficiency of Hassanpour Houshmand (HH) protocol is not high, and there exist several approaches through which more efficient protocols for the same task can be designed. To establish this point, we have proposed an efficient protocol of controlled deterministic secure quantum communication which is based on permutation of particles (PoP) technique and is considerably efficient compared to HH protocol. We have also generalized this protocol into its bidirectional counterpart. Interestingly, bipartite entanglement (Bell state) is sufficient for the realization of the proposed protocols, but HH protocol and other existing protocols require at least tripartite entanglement. Further, we have shown that it is possible to construct a large number of efficient protocols of unidirectional and bidirectional controlled deterministic secure quantum communication by using various alternative approaches and different quantum states. These alternative protocols can be realized by modifying the existing protocols of quantum secure direct communication and deterministic secure quantum communication. We have also shown that it is possible to design completely orthogonal-state-based protocols for unidirectional and bidirectional controlled deterministic secure quantum communication.
Quantum mechanical Carnot engine
Bender, C M; Meister, B K
2000-01-01T23:59:59.000Z
A cyclic thermodynamic heat engine runs most efficiently if it is reversible. Carnot constructed such a reversible heat engine by combining adiabatic and isothermal processes for a system containing an ideal gas. Here, we present an example of a cyclic engine based on a single quantum-mechanical particle confined to a potential well. The efficiency of this engine is shown to equal the Carnot efficiency because quantum dynamics is reversible. The quantum heat engine has a cycle consisting of adiabatic and isothermal quantum processes that are close analogues of the corresponding classical processes.
Quantum mechanical Carnot engine
C. M. Bender; D. C. Brody; B. K. Meister
2000-07-03T23:59:59.000Z
A cyclic thermodynamic heat engine runs most efficiently if it is reversible. Carnot constructed such a reversible heat engine by combining adiabatic and isothermal processes for a system containing an ideal gas. Here, we present an example of a cyclic engine based on a single quantum-mechanical particle confined to a potential well. The efficiency of this engine is shown to equal the Carnot efficiency because quantum dynamics is reversible. The quantum heat engine has a cycle consisting of adiabatic and isothermal quantum processes that are close analogues of the corresponding classical processes.
Optimal suppression of defect generation during a passage across a quantum critical point
Ning Wu; Arun Nanduri; Herschel Rabitz
2014-12-09T23:59:59.000Z
The dynamics of quantum phase transitions are inevitably accompanied by the formation of defects when crossing a quantum critical point. For a generic class of quantum critical systems, we solve the problem of minimizing the production of defects through the use of a gradient-based deterministic optimal control algorithm. By considering a finite size quantum Ising model with a tunable global transverse field, we show that an optimal power law quench of the transverse field across the Ising critical point works well at minimizing the number of defects, in spite of being drawn from a subset of quench profiles. These power law quenches are shown to be inherently robust against noise. The optimized defect density exhibits a transition at a critical ratio of the quench duration to the system size, which we argue coincides with the intrinsic speed limit for quantum evolution.
Metric perturbation theory of quantum dynamics
Antony L Tambyrajah
2006-10-06T23:59:59.000Z
A theory of quantum dynamics based on a discrete structure underlying the space time manifold is developed for single particles. It is shown that at the micro domain the interaction of particles with the underlying discrete structure results in the quantum space time manifold. Regarding the resulting quantum space-time as perturbation from the Lorentz metric it is shown it is possible to discuss the dynamics of particles in the quantum domain.
Continuous-variable quantum-state sharing via quantum disentanglement
Lance, Andrew M.; Symul, Thomas; Lam, Ping Koy [Quantum Optics Group, Department of Physics, Faculty of Science, Australian National University, ACT 0200 (Australia); Bowen, Warwick P. [Quantum Optics Group, Department of Physics, Faculty of Science, Australian National University, ACT 0200 (Australia); Quantum Optics Group, Norman Bridge Laboratory of Physics, California Institute of Technology, Pasadena, California 91125 (United States); Sanders, Barry C. [Institute for Quantum Information Science, University of Calgary, Alberta T2N 1N4 (Canada); Tyc, Tomas [Institute of Theoretical Physics, Masaryk University, 61137 Brno (Czech Republic); Ralph, T.C. [Department of Physics, University of Queensland, St. Lucia QLD 4072 (Australia)
2005-03-01T23:59:59.000Z
Quantum-state sharing is a protocol where perfect reconstruction of quantum states is achieved with incomplete or partial information in a multipartite quantum network. Quantum-state sharing allows for secure communication in a quantum network where partial information is lost or acquired by malicious parties. This protocol utilizes entanglement for the secret-state distribution and a class of 'quantum disentangling' protocols for the state reconstruction. We demonstrate a quantum-state sharing protocol in which a tripartite entangled state is used to encode and distribute a secret state to three players. Any two of these players can collaborate to reconstruct the secret state, while individual players obtain no information. We investigate a number of quantum disentangling processes and experimentally demonstrate quantum-state reconstruction using two of these protocols. We experimentally measure a fidelity, averaged over all reconstruction permutations, of F=0.73{+-}0.02. A result achievable only by using quantum resources.
Axel Friedenauer; Hector Schmitz; Jan Tibor Glückert; Diego Porras; Tobias Schätz
2008-02-27T23:59:59.000Z
To gain deeper insight into the dynamics of complex quantum systems we need a quantum leap in computer simulations. We can not translate quantum behaviour arising with superposition states or entanglement efficiently into the classical language of conventional computers. The final solution to this problem is a universal quantum computer [1], suggested in 1982 and envisioned to become functional within the next decade(s); a shortcut was proposed via simulating the quantum behaviour of interest in a different quantum system, where all parameters and interactions can be controlled and the outcome detected sufficiently well. Here we study the feasibility of a quantum simulator based on trapped ions [2]. We experimentally simulate the adiabatic evolution of the smallest non-trivial spin system from the paramagnetic into the (anti-)ferromagnetic order with a quantum magnetisation for two spins of 98%, controlling and manipulating all relevant parameters of the Hamiltonian independently via electromagnetic fields. We prove that the observed transition is not driven by thermal fluctuations, but of quantum mechanical origin, the source of quantum fluctuations in quantum phase transitions [3]. We observe a final superposition state of the two degenerate spin configurations for the ferromagnetic and the antiferromagnetic order, respectively. These correspond to deterministically entangled states achieved with a fidelity up to 88%. Our work demonstrates a building block for simulating quantum spin-Hamiltonians with trapped ions. The method has potential for scaling to a higher number of coupled spins [2].
Superradiant Quantum Heat Engine
Ali Ü. C. Hardal; Özgür E. Müstecapl?oglu
2015-04-22T23:59:59.000Z
Quantum physics revolutionized classical disciplines of mechanics, statistical physics, and electrodynamics. One branch of scientific knowledge however seems untouched: thermodynamics. Major motivation behind thermodynamics is to develop efficient heat engines. Technology has a trend to miniaturize engines, reaching to quantum regimes. Development of quantum heat engines (QHEs) requires emerging field of quantum thermodynamics. Studies of QHEs debate whether quantum coherence can be used as a resource. We explore an alternative where it can function as an effective catalyst. We propose a QHE which consists of a photon gas inside an optical cavity as the working fluid and quantum coherent atomic clusters as the fuel. Utilizing the superradiance, where a cluster can radiate quadratically faster than a single atom, we show that the work output becomes proportional to the square of the number of the atoms. In addition to practical value of cranking up QHE, our result is a fundamental difference of a quantum fuel from its classical counterpart.
Permanent Home Number: Residential Number
Viglas, Anastasios
Permanent Home Number: Residential Number: Mobile: Please update my contact details. Signature nominated correspondence address as indicated below. Permanent Home Adress Residential Address Other Address (Must not be a PO Box) Residential Address (Must not be a PO Box) Other - Postal/Optional Address
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
193 UNIT NUMBER: 197 UNIT NAME: CONCRETE RUBBLE PILE (30) REGULATORY STATUS: AOC LOCATION: Outside plant security fence, north of the plant on Big Bayou Creek on private property....
Latyshev, A V
2015-01-01T23:59:59.000Z
From Vlasov kinetic equation for collisionless plasmas distribution function in square-law approximation on size of electromagnetic field is received. Formulas for calculation electric current at any temperature (any degree of degeneration of electronic gas) are deduced. The case of small values of the wave numbers is considered. It is shown, that the nonlinearity account leads to occurrence the longitudinal electric current directed along a wave vector. This longitudinal current orthogonal to known transversal classical current, received at the linear analysis. From the kinetic equation with Wigner integral for collisionless quantum plasma distribution function is received in square-law on vector potential approximation. Formulas for calculation electric current at any temperature are deduced. The case of small values of wave number is considered. It is shown, that size of a longitudinal current at small values of wave number and for classical plasma and for quantum plasma coincide. Graphic comparison of dim...
Coherent states in the quantum multiverse
S. Robles-Perez; Y. Hassouni; P. F. Gonzalez-Diaz
2009-11-24T23:59:59.000Z
In this paper, we study the role of coherent states in the realm of quantum cosmology, both in a second-quantized single universe and in a third-quantized quantum multiverse. In particular, most emphasis will be paid to the quantum description of multiverses made up of accelerated universes. We have shown that the quantum states involved at a quantum mechanical multiverse whose single universes are accelerated are given by squeezed states having no classical analogs.
Fault-tolerant quantum computer architectures using hierarchies of quantum error-correcting codes
Cross, Andrew W. (Andrew William), 1979-
2008-01-01T23:59:59.000Z
Quantum computers have been shown to efficiently solve a class of problems for which no efficient solution is otherwise known. Physical systems can implement quantum computation, but devising realistic schemes is an extremely ...
Critically damped quantum search
Ari Mizel
2008-10-02T23:59:59.000Z
Although measurement and unitary processes can accomplish any quantum evolution in principle, thinking in terms of dissipation and damping can be powerful. We propose a modification of Grover's algorithm in which the idea of damping plays a natural role. Remarkably, we have found that there is a critical damping value that divides between the quantum $O(\\sqrt{N})$ and classical O(N) search regimes. In addition, by allowing the damping to vary in a fashion we describe, one obtains a fixed-point quantum search algorithm in which ignorance of the number of targets increases the number of oracle queries only by a factor of 1.5.
Strongly Universal Quantum Turing Machines and Invariance of Kolmogorov Complexity
Markus Mueller
2007-08-11T23:59:59.000Z
We show that there exists a universal quantum Turing machine (UQTM) that can simulate every other QTM until the other QTM has halted and then halt itself with probability one. This extends work by Bernstein and Vazirani who have shown that there is a UQTM that can simulate every other QTM for an arbitrary, but preassigned number of time steps. As a corollary to this result, we give a rigorous proof that quantum Kolmogorov complexity as defined by Berthiaume et al. is invariant, i.e. depends on the choice of the UQTM only up to an additive constant. Our proof is based on a new mathematical framework for QTMs, including a thorough analysis of their halting behaviour. We introduce the notion of mutually orthogonal halting spaces and show that the information encoded in an input qubit string can always be effectively decomposed into a classical and a quantum part.
A Naturally Renormalized Quantum Field Theory
S. Rouhani; M. V. Takook
2006-07-07T23:59:59.000Z
It was shown that quantum metric fluctuations smear out the singularities of Green's functions on the light cone [1], but it does not remove other ultraviolet divergences of quantum field theory. We have proved that the quantum field theory in Krein space, {\\it i.e.} indefinite metric quantization, removes all divergences of quantum field theory with exception of the light cone singularity [2,3]. In this paper, it is discussed that the combination of quantum field theory in Krein space together with consideration of quantum metric fluctuations, results in quantum field theory without any divergences.
Simulated Quantum Computation of Molecular Energies
Alán Aspuru-Guzik; Anthony D. Dutoi; Peter J. Love; Martin Head-Gordon
2006-04-26T23:59:59.000Z
The calculation time for the energy of atoms and molecules scales exponentially with system size on a classical computer but polynomially using quantum algorithms. We demonstrate that such algorithms can be applied to problems of chemical interest using modest numbers of quantum bits. Calculations of the water and lithium hydride molecular ground-state energies have been carried out on a quantum computer simulator using a recursive phase-estimation algorithm. The recursive algorithm reduces the number of quantum bits required for the readout register from about 20 to 4. Mappings of the molecular wave function to the quantum bits are described. An adiabatic method for the preparation of a good approximate ground-state wave function is described and demonstrated for a stretched hydrogen molecule. The number of quantum bits required scales linearly with the number of basis functions, and the number of gates required grows polynomially with the number of quantum bits.
atomic number density: Topics by E-print Network
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
and relative number squeezing in dissociation of spatially inhomogeneous molecular condensates Quantum Physics (arXiv) Summary: We study atom-atom correlations and relative...
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level: National5Sales for4,645 3,625govInstrumentstdmadapInactiveVisiting the TWPSuccessAlamos LaboratoryCertified Reference6-02-01Change Number
Electric Time in Quantum Cosmology
Stephon Alexander; Martin Bojowald; Antonino Marciano; David Simpson
2012-12-10T23:59:59.000Z
Effective quantum cosmology is formulated with a realistic global internal time given by the electric vector potential. New possibilities for the quantum behavior of space-time are found, and the high-density regime is shown to be very sensitive to the specific form of state realized.
Modulational instability of electromagnetic waves in a collisional quantum magnetoplasma
Niknam, A. R., E-mail: a-niknam@sbu.ac.ir [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran (Iran, Islamic Republic of); Rastbood, E.; Bafandeh, F.; Khorashadizadeh, S. M., E-mail: smkhorashadi@birjand.ac.ir [Physics Department of Birjand University, Birjand (Iran, Islamic Republic of)
2014-04-15T23:59:59.000Z
The modulational instability of right-hand circularly polarized electromagnetic electron cyclotron (CPEM-EC) wave in a magnetized quantum plasma is studied taking into account the collisional effects. Employing quantum hydrodynamic and nonlinear Schrödinger equations, the dispersion relation of modulated CPEM-EC wave in a collisional plasma has been derived. It is found that this wave is unstable in such a plasma system and the growth rate of the associated instability depends on various parameters such as electron Fermi temperature, plasma number density, collision frequency, and modulation wavenumber. It is shown that while the increase of collision frequency leads to increase of the growth rate of instability, especially at large wavenumber limit, the increase of plasma number density results in more stable modulated CPEM-EC wave. It is also found that in contrast to collisionless plasma in which modulational instability is restricted to small wavenumbers, in collisional plasma, the interval of instability occurrence can be extended to a large domain.
Decoherence problem in quantum state transfer via an engineered spin chain
Lan Zhou; Jing Lu; Tao Shi; C. P. Sun
2006-08-17T23:59:59.000Z
A perfect quantum state transfer(QST) has been shown in an engineered spin chain with "always-on interaction". Here, we consider a more realistic problem for such a protocol, the quantum decoherence induced by a spatially distributed environment, which is universally modeled as a bath of harmonic oscillators. By making use of the irreducible tensor method in angular momentum theory, we investigate the effect of decoherence on the efficiency of QST for both cases at zero and finite temperatures. We not only show the generic exponential decay of QST efficiency as the number of sites increase, but also find some counterintuitive effect, the QST can be enhanced as temperature increase.
Superradiant Quantum Heat Engine
Ali Ü. C. Hardal; Özgür E. Müstecapl?oglu
2015-03-12T23:59:59.000Z
Quantum physics has revolutionized the classical disciplines of mechanics, statistical physics, and electrodynamics. It modernized our society with many advances such as lasers and transistors. One branch of scientific knowledge however seems untouched: thermodynamics. Major motivation behind thermodynamics is to develop efficient heat engines. Technology has a trend to miniaturize engines, reaching to the quantum regimes. Inevitably, development of quantum heat engines (QHEs) requires investigations of thermodynamical principles from quantum mechanical perspective, and motivates the emerging field of quantum thermodynamics. Studies of QHEs debate on whether quantum coherence can be used as a resource. We explore an alternative that quantum coherence can be a catalyst. We propose a QHE which consists of a photon gas inside an optical cavity as the working fluid and quantum coherent atomic clusters as the fuel. Utilizing the superradiance, where a cluster can radiate quadratically faster than a single atom, we show that the work capability of the QHE becomes proportional to the square of the number of the atoms. In addition to practical value of cranking up a QHE, our results reveal a fundamental difference of a quantum fuel from its classical counterpart.
Infrared divergence of a scalar quantum field model on a pseudo Riemannian manifold
C. Gérard; F. Hiroshima; A. Panati; A. Suzuki
2011-03-18T23:59:59.000Z
A scalar quantum field model defined on a pseudo Riemann manifold is considered. The model is unitarily transformed the one with a variable mass. By means of a Feynman-Kac-type formula, it is shown that when the variable mass is short range, the Hamiltonian has no ground state. Moreover the infrared divergence of the expectation values of the number of bosons in the ground state is discussed.
Stapp, Henry
2011-11-10T23:59:59.000Z
Robert Griffiths has recently addressed, within the framework of a ‘consistent quantum theory’ (CQT) that he has developed, the issue of whether, as is often claimed, quantum mechanics entails a need for faster-than-light transfers of information over long distances. He argues, on the basis of his examination of certain arguments that claim to demonstrate the existence of such nonlocal influences, that such influences do not exist. However, his examination was restricted mainly to hidden-variable-based arguments that include in their premises some essentially classical-physics-type assumptions that are fundamentally incompatible with the precepts of quantum physics. One cannot logically prove properties of a system by attributing to the system properties alien to that system. Hence Griffiths’ rejection of hidden-variable-based proofs is logically warranted. Griffiths mentions the existence of a certain alternative proof that does not involve hidden variables, and that uses only macroscopically described observable properties. He notes that he had examined in his book proofs of this general kind, and concluded that they provide no evidence for nonlocal influences. But he did not examine the particular proof that he cites. An examination of that particular proof by the method specified by his ‘consistent quantum theory’ shows that the cited proof is valid within that restrictive framework. This necessary existence, within the ‘consistent’ framework, of long range essentially instantaneous influences refutes the claim made by Griffiths that his ‘consistent’ framework is superior to the orthodox quantum theory of von Neumann because it does not entail instantaneous influences. An added section responds to Griffiths’ reply, which cites a litany of ambiguities that seem to restrict, devastatingly, the scope of his CQT formalism, apparently to buttress his claim that my use of that formalism to validate the nonlocality theorem is flawed. But the vagaries that he cites do not upset the proof in question. It is show here in detail why the precise statement of this theorem justifies the specified application of CQT. It is also shown, in response to his challenge, why a putative proof of locality that he has proposed is not valid.
hal-00941175,version1-3Feb2014 SCM and the principles identified by HPM. It is shown that
Boyer, Edmond
hal-00941175,version1-3Feb2014 #12;SCM and the principles identified by HPM. It is shown that two problems obtained in series. B. Dynamic permeability The derivation of the dynamic Darcy law from HPM
Termination of Nondeterministic Quantum Programs
Yangjia Li; Nengkun Yu; Mingsheng Ying
2012-01-04T23:59:59.000Z
We define a language-independent model of nondeterministic quantum programs in which a quantum program consists of a finite set of quantum processes. These processes are represented by quantum Markov chains over the common state space. An execution of a nondeterministic quantum program is modeled by a sequence of actions of individual processes. These actions are described by super-operators on the state Hilbert space. At each step of an execution, a process is chosen nondeterministically to perform the next action. A characterization of reachable space and a characterization of diverging states of a nondeterministic quantum program are presented. We establish a zero-one law for termination probability of the states in the reachable space of a nondeterministic quantum program. A combination of these results leads to a necessary and sufficient condition for termination of nondeterministic quantum programs. Based on this condition, an algorithm is found for checking termination of nondeterministic quantum programs within a fixed finite-dimensional state space. A striking difference between nondeterministic classical and quantum programs is shown by example: it is possible that each of several quantum programs simulates the same classical program which terminates with probability 1, but the nondeterministic program consisting of them terminates with probability 0 due to the interference carried in the execution of them.
EL-Labany, S. K.; El-Mahgoub, M. G. [Department of Physics, Faculty of Science, Mansoura University, Damietta Branch, Damietta El-Gedida 34517 (Egypt); EL-Shamy, E. F. [Department of Physics, Faculty of Science, Mansoura University, Damietta Branch, Damietta El-Gedida 34517 (Egypt); Department of Physics, College of Science, King Khalid University, Abha, P.O. 9004 (Saudi Arabia)
2012-06-15T23:59:59.000Z
The interaction between two planar and nonplanar (cylindrical and spherical) quantum electron acoustic solitary waves (QEASWs) in quantum dense electron-ion plasmas has been studied. The extended Poincare-Lighthill-Kuo method is used to obtain planar and nonplanar phase shifts after the interaction of the two QEASWs. The change of phase shifts and trajectories for QEASWs due to the effect of the different geometries, the quantum corrections of diffraction, and the cold electron-to-hot electron number density ratio are discussed. It is shown that the interaction of the QEASWs in planar geometry, cylindrical geometry, and spherical geometry are different. The present investigation may be beneficial to understand the interaction between two planar and nonplanar QEASWs that may occur in the quantum plasmas found in laser-produced plasmas as well as in astrophysical plasmas.
Analogy between turbulence and quantum gravity: beyond Kolmogorov's 1941 theory
S. Succi
2011-11-14T23:59:59.000Z
Simple arguments based on the general properties of quantum fluctuations have been recently shown to imply that quantum fluctuations of spacetime obey the same scaling laws of the velocity fluctuations in a homogeneous incompressible turbulent flow, as described by Kolmogorov 1941 (K41) scaling theory. Less noted, however, is the fact that this analogy rules out the possibility of a fractal quantum spacetime, in contradiction with growing evidence in quantum gravity research. In this Note, we show that the notion of a fractal quantum spacetime can be restored by extending the analogy between turbulence and quantum gravity beyond the realm of K41 theory. In particular, it is shown that compatibility of a fractal quantum-space time with the recent Horava-Lifshitz scenario for quantum gravity, implies singular quantum wavefunctions. Finally, we propose an operational procedure, based on Extended Self-Similarity techniques, to inspect the (multi)-scaling properties of quantum gravitational fluctuations.
Free motion in deformed (quantum) four-dimensional space
A. N. Leznov
2007-07-23T23:59:59.000Z
It is shown that trajectories of free motion of the particles in deformed ("quantum") four dimensional space-time are quadratic curves.
pyruvate (Stols and Donnelly 1997), while normal E. coli strains produce malic acid from phospho- enolAbstract We had previously shown that succinic acid production in a pfl ldhA double mutant strain gene, produced a considerable amount of malic acid along with the desired product, succinic acid
Cartigny, Pierre
Evidence for a mantle component shown by rare gases, C and N isotopes in polycrystalline diamonds. Farley Abstract In an attempt to constrain the origin of polycrystalline diamond, combined analyses in the source of the polycrystalline diamonds from Orapa. The y13 C and y15 N isotopic values of À1.04 to À9.79x
Beigl, Michael
consumption and for about 50% of the total electricity consumption [1]. Therefore it is important to explore one of them. The interviewees preferred receiving electricity consumption feedback from a bill, a web1 Abstract--Numerous studies have shown that households' consumption is an important part
The global change research community has shown that: · Most of the world's glaciers are stagnant or in hasty retreat. · Glaciers are responding to climate change. · Glacier retreat and other changes will accelerate over next 100 years as climate change accelerates. We estimate that glacier change directly
Continuous-time quantum walks on star graphs
Salimi, S. [Department of Physics, University of Kurdistan, P.O. Box 66177-15175, Sanandaj (Iran, Islamic Republic of)], E-mail: shsalimi@uok.ac.ir
2009-06-15T23:59:59.000Z
In this paper, we investigate continuous-time quantum walk on star graphs. It is shown that quantum central limit theorem for a continuous-time quantum walk on star graphs for N-fold star power graph, which are invariant under the quantum component of adjacency matrix, converges to continuous-time quantum walk on K{sub 2} graphs (complete graph with two vertices) and the probability of observing walk tends to the uniform distribution.
The Unreasonable Success of Quantum Probability II: Quantum Measurements as Universal Measurements
Diederik Aerts; Massimiliano Sassoli de Bianchi
2014-09-10T23:59:59.000Z
In the first part of this two-part article, we have introduced and analyzed a multidimensional model, called the 'general tension-reduction' (GTR) model, able to describe general quantum-like measurements with an arbitrary number of outcomes, and we have used it as a general theoretical framework to study the most general possible condition of lack of knowledge in a measurement, so defining what we have called a 'universal measurement'. In this second part, we present the formal proof that universal measurements, which are averages over all possible forms of fluctuations, produce the same probabilities as measurements characterized by 'uniform' fluctuations on the measurement situation. Since quantum probabilities can be shown to arise from the presence of such uniform fluctuations, we have proven that they can be interpreted as the probabilities of a first-order non-classical theory, describing situations in which the experimenter lacks complete knowledge about the nature of the interaction between the measuring apparatus and the entity under investigation. This same explanation can be applied -- mutatis mutandis -- to the case of cognitive measurements, made by human subjects on conceptual entities, or in decision processes, although it is not necessarily the case that the structure of the set of states would be in this case strictly Hilbertian. We also show that universal measurements correspond to maximally 'robust' descriptions of indeterministic reproducible experiments, and since quantum measurements can also be shown to be maximally robust, this adds plausibility to their interpretation as universal measurements, and provides a further element of explanation for the great success of the quantum statistics in the description of a large class of phenomena.
cooling of fermionic 6 Li in a thermal bath of bosonic 23 Na. The system features rapid thermalization, for sympathetic cooling of 6 Li. Our work provides the natural progression in t; published 4 April 2002) We have produced a macroscopic quantum system in which a 6 Li Fermi sea coexists
Hamiltonian Ratchets Holger Schanz,1 Marc-Felix Otto,1 Roland Ketzmerick,1 and Thomas Dittrich2 1 Max. Transport in quantum Hamiltonian ratchets arises by the same mechanism as long as uncertainty allows one of molecular motors, the study of ratchets [1] has widened to a general exploration of "self
Quantum thermodynamic cooling cycle
Jose P. Palao; Ronnie Kosloff; Jeffrey M. Gordon
2001-06-08T23:59:59.000Z
The quantum-mechanical and thermodynamic properties of a 3-level molecular cooling cycle are derived. An inadequacy of earlier models is rectified in accounting for the spontaneous emission and absorption associated with the coupling to the coherent driving field via an environmental reservoir. This additional coupling need not be dissipative, and can provide a thermal driving force - the quantum analog of classical absorption chillers. The dependence of the maximum attainable cooling rate on temperature, at ultra-low temperatures, is determined and shown to respect the recently-established fundamental bound based on the second and third laws of thermodynamics.
Quantum thermodynamic cooling cycle
Palao, J P; Gordon, J M; Palao, Jose P.; Kosloff, Ronnie; Gordon, Jeffrey M.
2001-01-01T23:59:59.000Z
The quantum-mechanical and thermodynamic properties of a 3-level molecular cooling cycle are derived. An inadequacy of earlier models is rectified in accounting for the spontaneous emission and absorption associated with the coupling to the coherent driving field via an environmental reservoir. This additional coupling need not be dissipative, and can provide a thermal driving force - the quantum analog of classical absorption chillers. The dependence of the maximum attainable cooling rate on temperature, at ultra-low temperatures, is determined and shown to respect the recently-established fundamental bound based on the second and third laws of thermodynamics.
Quantum statistical synchronization of non-interacting particles
Tichy, Malte C; de Melo, Fernando; Mintert, Florian; Buchleitner, Andreas
2012-01-01T23:59:59.000Z
A full treatment for the scattering of an arbitrary number of bosons through a Bell multiport beam splitter is presented that includes all possible output arrangements. Due to exchange symmetry, the event statistics differs dramatically from the classical case in which the realization probabilities are given by combinatorics. A law for the suppression of output configurations is derived and shown to apply for the majority of all possible arrangements. Such multiparticle interference effects dominate at the level of single transition amplitudes, while a generic bosonic signature can be observed when the average number of occupied ports or the typical number of particles per port is considered. The results allow to classify in a common approach several recent experiments and theoretical studies and disclose many accessible quantum statistical effects involving many particles.
Quantum statistical synchronization of non-interacting particles
Malte C. Tichy; Markus Tiersch; Fernando de Melo; Florian Mintert; Andreas Buchleitner
2012-04-17T23:59:59.000Z
A full treatment for the scattering of an arbitrary number of bosons through a Bell multiport beam splitter is presented that includes all possible output arrangements. Due to exchange symmetry, the event statistics differs dramatically from the classical case in which the realization probabilities are given by combinatorics. A law for the suppression of output configurations is derived and shown to apply for the majority of all possible arrangements. Such multiparticle interference effects dominate at the level of single transition amplitudes, while a generic bosonic signature can be observed when the average number of occupied ports or the typical number of particles per port is considered. The results allow to classify in a common approach several recent experiments and theoretical studies and disclose many accessible quantum statistical effects involving many particles.
Smagina, Zh. V.; Stepina, N. P., E-mail: stepina@isp.nsc.ru; Zinovyev, V. A.; Kuchinskaya, P. A. [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Lavrenteva 13, 630090 Novosibirsk (Russian Federation); Novikov, P. L.; Dvurechenskii, A. V. [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Lavrenteva 13, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogova, 2, 630090 Novosibirsk (Russian Federation)
2014-10-13T23:59:59.000Z
An original approach based on the combination of nanoimprint lithography and ion irradiation through mask has been developed for fabrication of large-area periodical pattern on Si(100). Using the selective etching of regions amorphized by ion irradiation ordered structures with grooves and ridges were obtained. The shape and depth of the relief were governed by ion energy and by the number of etching stages as well. Laterally ordered chains of Ge quantum dots were fabricated by molecular beam epitaxy of Ge on the pre-patterned Si substrates. For small amount of Ge deposited chains contain separate quantum dot molecules. The increase of deposition amount leads to overlapping of quantum dot molecules with formation of dense homogeneous chains of quantum dots. It was shown that the residual irradiation-induced bulk defects underneath the grooves suppress nucleation of Ge islands at the bottom of grooves. On pre-patterned substrates with whole defect regions, etched quantum dots grow at the bottom of grooves. The observed location of Ge quantum dots is interpreted in terms of local strain-mediated surface chemical potential which controls the sites of islands nucleation. The local chemical potential is affected by additional strain formed by the residual defects. It was shown by molecular dynamics calculations that these defects form the compressive strain at the bottom of grooves.
Quantum interference as a resource for quantum speedup
Dan Stahlke
2014-08-01T23:59:59.000Z
Quantum states can in a sense be thought of as generalizations of classical probability distributions, but are more powerful than probability distributions when used for computation or communication. Quantum speedup therefore requires some feature of quantum states that classical probability distributions lack. One such feature is interference. We quantify interference and show that there can be no quantum speedup due to a small number of operations incapable of generating large amounts of interference (although large numbers of such operations can in fact lead to quantum speedup). Low-interference operations include sparse unitaries, Grover reflections, short time/low energy Hamiltonian evolutions, and the Haar wavelet transform. Circuits built from such operations can be classically simulated via a Monte Carlo technique making use of a convex combination of two Markov chains. Applications to query complexity, communication complexity, and the Wigner representation are discussed.
A. Jadczyk
1994-06-30T23:59:59.000Z
The paper consists of two parts. In the first part Schroedinger's equation for a charged quantum particle in a Galilei-Newton curved space-time is derived in a fully geometrical way. Gravitational and electromagnetic fields are coded into space metric and space-time connection. The fundamental geometrical object is a quantum connection in a Hermitian line bundle over the 7-dimensional jet space of 3-velocities. The secondary object is the bundle of Hilbert spaces over absolute time. Time appears as a superselection quantity while Shroedinger equation is interpreted as parallel transport in this bundle. In the second part the problem of measurement in quantum theory is discussed as a part of a more general problem of coupling between quantum and classical systems. The standard framework of quantum theory is extended so as to allow for dynamical central observables within dissipative dynamics. It is shown that within this approach one obtains not only Liouville equation that describes statistical ensembles, but also a piecewise-deterministic random process describing sequences of "events" that can be monitored by a continuous observation of the single, coupled classical system. It also describes "quantum jumps" or "wave packet reductions" that accompany these events. Two example are worked out in some details. The last one deals with the problem oof "how to determine the wave function ?".
Transport and Dissipation in Quantum Pumps
J. E. Avron; A. Elgart; G. M. Graf; L. Sadun
2003-05-23T23:59:59.000Z
This paper is about adiabatic transport in quantum pumps. The notion of ``energy shift'', a self-adjoint operator dual to the Wigner time delay, plays a role in our approach: It determines the current, the dissipation, the noise and the entropy currents in quantum pumps. We discuss the geometric and topological content of adiabatic transport and show that the mechanism of Thouless and Niu for quantized transport via Chern numbers cannot be realized in quantum pumps where Chern numbers necessarily vanish.
A General Theorem Relating the Bulk Topological Number to Edge States in Two-dimensional Insulators
Qi, Xiao-Liang; /Tsinghua U., Beijing /Stanford U., Phys. Dept.; Wu, Yong-Shi; /Utah U.; Zhang, Shou-Cheng; /Stanford U., Phys. Dept. /Tsinghua U., Beijing
2010-01-15T23:59:59.000Z
We prove a general theorem on the relation between the bulk topological quantum number and the edge states in two dimensional insulators. It is shown that whenever there is a topological order in bulk, characterized by a non-vanishing Chern number, even if it is defined for a non-conserved quantity such as spin in the case of the spin Hall effect, one can always infer the existence of gapless edge states under certain twisted boundary conditions that allow tunneling between edges. This relation is robust against disorder and interactions, and it provides a unified topological classification of both the quantum (charge) Hall effect and the quantum spin Hall effect. In addition, it reconciles the apparent conflict between the stability of bulk topological order and the instability of gapless edge states in systems with open boundaries (as known happening in the spin Hall case). The consequences of time reversal invariance for bulk topological order and edge state dynamics are further studied in the present framework.
Conic approach to quantum graph parameters using linear ...
2015-04-07T23:59:59.000Z
system (1.1) is feasible defines the quantum parameter ?q(G). .... quantum stability numbers and in Section 4.2 for the quantum chromatic numbers. ..... 4 but not a power of 2, then ?q(?n)?q(?n) < |V (?n)| and the exact same reasoning implies ...
Grassl, Markus
.62% of being optimal. Key words: Quantum computation. Searching. Lower bound. 1. Introduction Let XN f0Y 1Y F F F Y N À 1g for some integer N and consider an arbitrary function F X XN 3 f0Y 1g. The goal is to find some i P XN such that Fi 1, provided such an i exists. If F is given as a black box ±± the only
Andrews, George E; Gawronski, Wolfgang; Littlejohn, Lance L
2011-01-01T23:59:59.000Z
The Jacobi-Stirling numbers were discovered as a result of a problem involving the spectral theory of powers of the classical second-order Jacobi differential expression. Specifically, these numbers are the coefficients of integral composite powers of the Jacobi expression in Lagrangian symmetric form. Quite remarkably, they share many properties with the classical Stirling numbers of the second kind which, as shown in LW, are the coefficients of integral powers of the Laguerre differential expression. In this paper, we establish several properties of the Jacobi-Stirling numbers and its companions including combinatorial interpretations thereby extending and supplementing known contributions to the literature of Andrews-Littlejohn, Andrews-Gawronski-Littlejohn, Egge, Gelineau-Zeng, and Mongelli.
Ronnie Kosloff
2013-05-10T23:59:59.000Z
Quantum thermodynamics addresses the emergence of thermodynamical laws from quantum mechanics. The link is based on the intimate connection of quantum thermodynamics with the theory of open quantum systems. Quantum mechanics inserts dynamics into thermodynamics giving a sound foundation to finite-time-thermodynamics. The emergence of the 0-law I-law II-law and III-law of thermodynamics from quantum considerations is presented. The emphasis is on consistence between the two theories which address the same subject from different foundations. We claim that inconsistency is the result of faulty analysis pointing to flaws in approximations.
Fresnel-transform's quantum correspondence and quantum optical ABCD Law
Fan Hongyi; Hu Liyun
2007-05-29T23:59:59.000Z
Corresponding to Fresnel transform there exists a unitary operator in quantum optics theory, which could be named Fresnel operator (FO). We show that the multiplication rule of FO naturally leads to the quantum optical ABCD law. The canonical operator methods as mapping of ray-transfer ABCD matrix is explicitly shown by FO's normally ordered expansion through the coherent state representation and the technique of integration within an ordered product of operators. We show that time evolution of the damping oscillator embodies the quantum optical ABCD law.
Quantum random-walk search algorithm
Shenvi, Neil; Whaley, K. Birgitta [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Kempe, Julia [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Computer Science Division, EECS, University of California, Berkeley, California 94720 (United States); CNRS-LRI, UMR 8623, Universite de Paris-Sud, 91405 Orsay (France)
2003-05-01T23:59:59.000Z
Quantum random walks on graphs have been shown to display many interesting properties, including exponentially fast hitting times when compared with their classical counterparts. However, it is still unclear how to use these novel properties to gain an algorithmic speedup over classical algorithms. In this paper, we present a quantum search algorithm based on the quantum random-walk architecture that provides such a speedup. It will be shown that this algorithm performs an oracle search on a database of N items with O({radical}(N)) calls to the oracle, yielding a speedup similar to other quantum search algorithms. It appears that the quantum random-walk formulation has considerable flexibility, presenting interesting opportunities for development of other, possibly novel quantum algorithms.
Quantum Error Correcting Subsystem Codes From Two Classical Linear Codes
Dave Bacon; Andrea Casaccino
2006-10-17T23:59:59.000Z
The essential insight of quantum error correction was that quantum information can be protected by suitably encoding this quantum information across multiple independently erred quantum systems. Recently it was realized that, since the most general method for encoding quantum information is to encode it into a subsystem, there exists a novel form of quantum error correction beyond the traditional quantum error correcting subspace codes. These new quantum error correcting subsystem codes differ from subspace codes in that their quantum correcting routines can be considerably simpler than related subspace codes. Here we present a class of quantum error correcting subsystem codes constructed from two classical linear codes. These codes are the subsystem versions of the quantum error correcting subspace codes which are generalizations of Shor's original quantum error correcting subspace codes. For every Shor-type code, the codes we present give a considerable savings in the number of stabilizer measurements needed in their error recovery routines.
Harumichi Nishimura; Masanao Ozawa
2008-12-05T23:59:59.000Z
In order to establish the computational equivalence between quantum Turing machines (QTMs) and quantum circuit families (QCFs) using Yao's quantum circuit simulation of QTMs, we previously introduced the class of uniform QCFs based on an infinite set of elementary gates, which has been shown to be computationally equivalent to the polynomial-time QTMs (with appropriate restriction of amplitudes) up to bounded error simulation. This result implies that the complexity class BQP introduced by Bernstein and Vazirani for QTMs equals its counterpart for uniform QCFs. However, the complexity classes ZQP and EQP for QTMs do not appear to equal their counterparts for uniform QCFs. In this paper, we introduce a subclass of uniform QCFs, the finitely generated uniform QCFs, based on finite number of elementary gates and show that the class of finitely generated uniform QCFs is perfectly equivalent to the class of polynomial-time QTMs; they can exactly simulate each other. This naturally implies that BQP as well as ZQP and EQP equal the corresponding complexity classes of the finitely generated uniform QCFs.
Quantum entanglement in the multiverse
Salvador Robles-Perez; Pedro F. Gonzalez-Diaz
2012-07-26T23:59:59.000Z
In this paper it is shown that the quantum state of a multiverse made up of classically disconnected regions of the space-time, whose dynamical evolution is dominated by a homogeneous and isotropic fluid, is given by a squeezed state. These are typical quantum states that have no classical counterpart and, therefore, they allow us to analyze the violation of classical inequalities as well as the EPR argument in the context of the quantum multiverse. The thermodynamical properties of entanglement are calculated for a composite quantum state of two universes whose states are quantum mechanically correlated. The energy of entanglement between the positive and negative modes of a scalar field, which correspond to the expanding and contracting branches of a phantom universe, respectively, are also computed.
Peter Holland
2014-09-21T23:59:59.000Z
With reference to primary sources it is shown that key claims made regarding the history of the pilot wave theory in Quantum Theory at the Crossroads are not supported by the historical record. It is also argued that the association of de Broglie with just a first-order law of particle motion, and Bohm with a second-order one, has no historical basis.
Quantum robots and quantum computers
Benioff, P.
1998-07-01T23:59:59.000Z
Validation of a presumably universal theory, such as quantum mechanics, requires a quantum mechanical description of systems that carry out theoretical calculations and systems that carry out experiments. The description of quantum computers is under active development. No description of systems to carry out experiments has been given. A small step in this direction is taken here by giving a description of quantum robots as mobile systems with on board quantum computers that interact with different environments. Some properties of these systems are discussed. A specific model based on the literature descriptions of quantum Turing machines is presented.
Quantum correlations; quantum probability approach
W. A. Majewski
2015-05-21T23:59:59.000Z
This survey gives a comprehensive account of quantum correlations understood as a phenomenon stemming from the rules of quantization. Centered on quantum probability it describes the physical concepts related to correlations (both classical and quantum), mathematical structures, and their consequences. These include the canonical form of classical correlation functionals, general definitions of separable (entangled) states, definition and analysis of quantumness of correlations, description of entanglement of formation, and PPT states. This work is intended both for physicists interested not only in collection of results but also in the mathematical methods justifying them, and mathematicians looking for an application of quantum probability to concrete new problems of quantum theory.
Large-amplitude solitons in gravitationally balanced quantum plasmas
Akbari-Moghanjoughi, M. [Department of Physics, Faculty of Sciences, Azarbaijan Shahid Madani University, 51745-406 Tabriz (Iran, Islamic Republic of); International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Ruhr University Bochum, D-44780 Bochum (Germany)
2014-08-15T23:59:59.000Z
Using the quantum fluid model for self-gravitating quantum plasmas with the Bernoulli pseudopotential method and taking into account the relativistic degeneracy effect, it is shown that gravity-induced large-amplitude density rarefaction solitons can exist in gravitationally balanced quantum plasmas. These nonlinear solitons are generated due to the force imbalance between the gravity and the quantum fluid pressure via local density perturbations, similar to that on shallow waters. It is found that both the fluid mass-density and the atomic-number of the constituent ions have significant effect on the amplitude and width of these solitonic profiles. Existence of a large-scale gravity-induced solitonic activities on neutron-star surface, for instance, can be a possible explanation for the recently proposed resonant shattering mechanism [D. Tsang et al., Phys. Rev. Lett. 108, 011102 (2012)] causing the intense short gamma ray burst phenomenon, in which release of ?10{sup 46}–10{sup 47} ergs would be possible from the surface. The resonant shattering of the crust in a neutron star has been previously attributed to the crust-core interface mode and the tidal surface tensions. We believe that current model can be a more natural explanation for the energy liberation by solitonic activities on the neutron star surfaces, without a requirement for external mergers like other neutron stars or black holes for the crustal shatter.
Zurek, Wojciech H [Los Alamos National Laboratory
2008-01-01T23:59:59.000Z
Quantum Darwinism - proliferation, in the environment, of multiple records of selected states of the system (its information-theoretic progeny) - explains how quantum fragility of individual state can lead to classical robustness of their multitude.
Simulations of Quantum Turing Machines by Quantum Multi-Stack Machines
Daowen Qiu
2005-06-06T23:59:59.000Z
As was well known, in classical computation, Turing machines, circuits, multi-stack machines, and multi-counter machines are equivalent, that is, they can simulate each other in polynomial time. In quantum computation, Yao [11] first proved that for any quantum Turing machines $M$, there exists quantum Boolean circuit $(n,t)$-simulating $M$, where $n$ denotes the length of input strings, and $t$ is the number of move steps before machine stopping. However, the simulations of quantum Turing machines by quantum multi-stack machines and quantum multi-counter machines have not been considered, and quantum multi-stack machines have not been established, either. Though quantum counter machines were dealt with by Kravtsev [6] and Yamasaki {\\it et al.} [10], in which the machines count with $0,\\pm 1$ only, we sense that it is difficult to simulate quantum Turing machines in terms of this fashion of quantum computing devices, and we therefore prove that the quantum multi-counter machines allowed to count with $0,\\pm 1,\\pm 2,...,\\pm n$ for some $n>1$ can efficiently simulate quantum Turing machines. Therefore, our mail goals are to establish quantum multi-stack machines and quantum multi-counter machines with counts $0,\\pm 1,\\pm 2,...,\\pm n$ and $n>1$, and particularly to simulate quantum Turing machines by these quantum computing devices.
Efficiency of quantum state tomography for qubits
Koichi Yamagata
2011-05-19T23:59:59.000Z
The efficiency of quantum state tomography is discussed from the point of view of quantum parameter estimation theory, in which the trace of the weighted covariance is to be minimized. It is shown that tomography is optimal only when a special weight is adopted.
Fujii, Kanji
2014-01-01T23:59:59.000Z
On the basis of quantum field theory, we consider a unified description of various processes accompanied by neutrinos, namely weak decays and oscillation processes. The structures of the expectation values of flavor-neutrino numbers with respect to neutrino-source hadron state are investigated. Due to the smallness of neutrino masses, we naturally obtain the old (i.e. pre-mixing) formulas of decay probabilities. Together, it is shown that the oscillation formulas, similar to the usual ones, are applied irrespectively of the details of neutrino-producing processes. The derived oscillation formulas are the same in form as the usually used ones except for the oscillation length.
Quantum to Classical Transition in a Single-Ion Laser
François Dubin; Carlos Russo; Helena G. Barros; Andreas Stute; Christoph Becher; Piet O. Schmidt; Rainer Blatt
2010-02-18T23:59:59.000Z
Stimulated emission of photons from a large number of atoms into the mode of a strong light field is the principle mechanism for lasing in "classical" lasers. The onset of lasing is marked by a threshold which can be characterised by a sharp increase in photon flux as a function of external pumping strength. The same is not necessarily true for the fundamental building block of a laser: a single trapped atom interacting with a single optical radiation mode. It has been shown that such a "quantum" laser can exhibit thresholdless lasing in the regime of strong coupling between atom and radiation field. However, although theoretically predicted, a threshold at the single-atom level could not be experimentally observed so far. Here, we demonstrate and characterise a single-atom laser with and without threshold behaviour by changing the strength of atom-light field coupling. We observe the establishment of a laser threshold through the accumulation of photons in the optical mode even for a mean photon number substantially lower than for the classical case. Furthermore, self-quenching occurs for very strong external pumping and constitutes an intrinsic limitation of single-atom lasers. Moreover, we find that the statistical properties of the emitted light can be adjusted for weak external pumping, from the quantum to the classical domain. Our observations mark an important step towards fundamental understanding of laser operation in the few-atom limit including systems based on semiconductor quantum dots or molecules.
Quantum Turing Machines: Local Transition, Preparation, Measurement, and Halting
Masanao Ozawa
1998-09-14T23:59:59.000Z
Foundations of the theory of quantum Turing machines are investigated. The protocol for the preparation and the measurement of quantum Turing machines is discussed. The local transition functions are characterized for fully general quantum Turing machines. A new halting protocol is proposed without augmenting the halting qubit and is shown to work without spoiling the computation.
Chaos, Fractal and Quantum Poincare Recurrences in Diamagnetic Kepler Problem
A. Ugulava; L. Chotorlishvili; T. Kereselidze; V. Skrinnikov
2006-08-01T23:59:59.000Z
The statistics of quantum Poincare recurrences in Hilbert space for diamagnetic hydrogen atom in strong magnetic field has been investigated. It has been shown that quantities characterizing classical chaos are in a good agreement with the ones that are used to describe quantum chaos. The equality of classical and quantum Poincare recurrences has been shown. It has been proved that one of the signs of the emergence of quantum chaos is the irreversible transition from a pure quantum mechanical state to the mixed one.
VOLUME 81, NUMBER 7 P H Y S I C A L R E V I E W L E T T E R S 17 AUGUST 1998 Cooling the Collective, suggesting the importance of these modes in future experiments. [S0031-9007(98)06838-0] PACS numbers: 03 in the ground state by laser cooling [5]. The next step towards imple- menting the Cirac-Zoller scheme
Block Free Optical Quantum Banyan Network based on Quantum State Fusion and Fission
Chang-Hua Zhu; Yan-Hong Meng; Dong-Xiao Quan; Nan Zhao; Chang-Xing Pei
2014-08-02T23:59:59.000Z
Optical switch fabric plays an important role in building multiple-user optical quantum communication networks. Owing to its self-routing property and low complexity, Banyan network is widely used for building switch fabric. While, there is no efficient way to remove internal blocking in Banyan network by classical way. Quantum state fusion, by which the two-dimensional internal quantum state of two photons could be combined into four-dimensional internal state of a single photon, makes it possible to solve this problem. In this paper, we convert the output mode of quantum state fusion from spatial-polarization mode to time-polarization mode. By combining modified quantum state fusion, quantum state fission with quantum Fredkin gate, we propose a practical scheme to build an optical quantum switch unit which is block free. The scheme can be extended to build more complex units, four of which are shown in this paper.
REVIEW OF BARRY MAZUR'S IMAGINING NUMBERS (PARTICULARLY THE SQUARE ROOT OF MINUS FIFTEEN) AND
Franklin, James
profile in the world's imagination. And it has brought in its train a number of philosophical questions of the explanatory load of quantum mechanics,
Kishore Thapliyal; Anirban Pathak
2015-01-17T23:59:59.000Z
Recently, several aspects of controlled quantum communication (e.g., bidirectional controlled state teleportation, controlled quantum secure direct communication, controlled quantum dialogue, etc.) have been studied using $n$-qubit ($n\\geq3$) entanglement. Specially, a large number of schemes for bidirectional controlled state teleportation are proposed using $m$-qubit entanglement ($m\\in\\{5,6,7\\}$). Here, we propose a set of protocols to illustrate that it is possible to realize all these tasks related to controlled quantum communication using only Bell states and permutation of particles (PoP). As the generation and maintenance of a Bell state is much easier than a multi-partite entanglement, the proposed strategy has a clear advantage over the existing proposals. Further, it is shown that all the schemes proposed here may be viewed as applications of the concept of quantum cryptographic switch which was recently introduced by some of us. The performances of the proposed protocols as subjected to the amplitude damping and phase damping noise on the channels are also discussed.
Quantum theory from one global symmetry
Chris Fields
2014-06-17T23:59:59.000Z
It is shown that unitary quantum theory is not only consistent with but follows from decompositional equivalence: the principle that there is no preferred decomposition of the universe into systems, or alternatively, that there is no preferred quantum reference frame. Decompositional equivalence requires unitary quantum theory to be both observer- and scale-independent, requires time, "systems" and all classical information to be strictly observer-relative, and imposes an unavoidable free-energy cost on the acquisition of observational outcomes. This free energy cost of observation is characterized from first principles and shown to accord with known costs of information acquisition and storage by human observers.
Quantum information science and complex quantum systems
Michael A. Nielsen
2002-10-01T23:59:59.000Z
What makes quantum information science a science? This paper explores the idea that quantum information science may offer a powerful approach to the study of complex quantum systems.
D. Gross; J. Eisert
2010-05-01T23:59:59.000Z
We introduce the notion of quantum computational webs: These are quantum states universal for measurement-based computation which can be built up from a collection of simple primitives. The primitive elements - reminiscent of building blocks in a construction kit - are (i) states on a one-dimensional chain of systems ("computational quantum wires") with the power to process one logical qubit and (ii) suitable couplings which connect the wires to a computationally universal "web". All elements are preparable by nearest-neighbor interactions in a single pass - a type of operation well-suited for a number of physical architectures. We provide a complete classification of qubit wires. This is first instance where a physically well-motivated class of universal resources can be fully understood. Finally, we sketch possible realizations in superlattices, and explore the power of coupling mechanisms based on Ising or exchange-interactions.
Quantum Fourier transform and tomographic Renyi entropic inequalities
M. A. Man'ko; V. I. Man'ko
2009-02-25T23:59:59.000Z
Renyi entropy associated with spin tomograms of quantum states is shown to obey to new inequalities containing the dependence on quantum Fourier transform. The limiting inequality for the von Neumann entropy of spin quantum states and a new kind of entropy associated with quantum Fourier transform are obtained. Possible connections with subadditivity and strong subadditivity conditions for tomographic entropies and von Neumann entropies are discussed.
Wunderlich, Christof
radiation in the radiofrequency or microwave regime. DOI: 10.1103/PhysRevLett.87.257904 PACS numbers: 03 Logic Using Long-Wavelength Radiation Florian Mintert1 and Christof Wunderlich2,* 1 I. Institut fÃ¼r radiation; the atom with mass m is trapped in a harmonic potential characterized by angular frequency vl
Infrared fixed point in quantum Einstein gravity
S. Nagy; J. Krizsan; K. Sailer
2012-06-28T23:59:59.000Z
We performed the renormalization group analysis of the quantum Einstein gravity in the deep infrared regime for different types of extensions of the model. It is shown that an attractive infrared point exists in the broken symmetric phase of the model. It is also shown that due to the Gaussian fixed point the IR critical exponent $\
Gate Fidelities, Quantum Broadcasting, and Assessing Experimental Realization
Hyang-Tag Lim; Young-Sik Ra; Yong-Su Kim; Yoon-Ho Kim; Joonwoo Bae
2011-06-29T23:59:59.000Z
We relate gate fidelities of experimentally realized quantum operations to the broadcasting property of their ideal operations, and show that the more parties a given quantum operation can broadcast to, the higher gate fidelities of its experimental realization are in general. This is shown by establishing the correspondence between two operational quantities, quantum state shareability and quantum broadcasting. This suggests that, to assess an experimental realization using gate fidelities, the worst case of realization such as noisy operations should be taken into account and then compared to obtained gate fidelities. In addition, based on the correspondence, we also translate results in quantum state shareability to their counterparts in quantum operations.
Quantum walks and quantum search on graphene lattices
Iain Foulger; Sven Gnutzmann; Gregor Tanner
2015-07-01T23:59:59.000Z
Quantum walks have been very successful in the development of search algorithms in quantum information, in particular in the development of spatial search algorithms. However, the construction of continuous-time quantum search algorithms in two-dimensional lattices has proved difficult, requiring additional degrees of freedom. Here, we demonstrate that continuous-time quantum walk search is possible in two-dimensions by changing the search topology to a graphene lattice, utilising the Dirac point in the energy spectrum. This is made possible by making a change to standard methods of marking a particular site in the lattice. Various ways of marking a site are shown to result in successful search protocols. We further establish that the search can be adapted to transfer probability amplitude across the lattice between specific lattice sites thus establishing a line of communication between these sites.
Quantum walks and quantum search on graphene lattices
Iain Foulger; Sven Gnutzmann; Gregor Tanner
2015-01-29T23:59:59.000Z
Quantum walks have been very successful in the development of search algorithms in quantum information, in particular in the development of spatial search algorithms. However, the construction of continuous-time quantum search algorithms in two-dimensional lattices has proved difficult, requiring additional degrees of freedom. Here, we demonstrate that continuous-time quantum walk search is possible in two-dimensions by changing the search topology to a graphene lattice, utilising the Dirac point in the energy spectrum. This is made possible by making a change to standard methods of marking a particular site in the lattice. Various ways of marking a site are shown to result in successful search protocols. We further establish that the search can be adapted to transfer probability amplitude across the lattice between specific lattice sites thus establishing a line of communication between these sites.
Quantum potential energy as concealed motion
Peter Holland
2014-11-13T23:59:59.000Z
It is known that the Schroedinger equation may be derived from a hydrodynamic model in which the Lagrangian position coordinates of a continuum of particles represent the quantum state. Using Routh\\s method of ignorable coordinates it is shown that the quantum potential energy of particle interaction that represents quantum effects in this model may be regarded as the kinetic energy of additional concealed freedoms. The method brings an alternative perspective to Planck\\s constant, which plays the role of a hidden variable, and to the canonical quantization procedure, since what is termed kinetic energy in quantum mechanics may be regarded literally as energy due to motion.
Some Aspects of Planck Scale Quantum Optics
Kourosh Nozari
2005-08-11T23:59:59.000Z
This paper considers the effects of gravitational induced uncertainty on some well-known quantum optics issues. First we will show that gravitational effects at quantum level destroy the notion of harmonic oscillations. Then it will be shown that, although it is possible(at least in principle) to have complete coherency and vanishing broadening in usual quantum optics, gravitational induced uncertainty destroys complete coherency and it is impossible to have a monochromatic ray. We will show that there is an additional wave packet broadening due to quantum gravitational effects.
Khan, Shabbir A
2013-01-01T23:59:59.000Z
Quantum plasma physics is a rapidly evolving research field with a very inter-disciplinary scope of potential applications, ranging from nano-scale science in condensed matter to the vast scales of astrophysical objects. The theoretical description of quantum plasmas relies on various approaches, microscopic or macroscopic, some of which have obvious relation to classical plasma models. The appropriate model should, in principle, incorporate the quantum mechanical effects such as diffraction, spin statistics and correlations, operative on the relevant scales. However, first-principle approaches such as quantum Monte Carlo and density functional theory or quantum-statistical methods such as quantum kinetic theory or non-equilibrium Green's functions require substantial theoretical and computational efforts. Therefore, for selected problems, alternative simpler methods have been put forward. In particular, the collective behavior of many-body systems is usually described within a self-consistent scheme of parti...
Phase space quantum mechanics - Direct
Nasiri, S.; Sobouti, Y.; Taati, F. [Institute for Advanced Studies in Basic Sciences, Zanjan, 45195-1159 (Iran, Islamic Republic of) and Department of Physics, Zanjan University, Zanjan (Iran); Institute for Advanced Studies in Basic Sciences, Zanjan, 45195-1159 (Iran, Islamic Republic of); Institute for Advanced Studies in Basic Sciences, Zanjan, 45195-1159 (Iran, Islamic Republic of) and Department of Physics, University of Kurdistan, D-78457 Sanadaj (Iran)
2006-09-15T23:59:59.000Z
Conventional approach to quantum mechanics in phase space (q,p), is to take the operator based quantum mechanics of Schroedinger, or an equivalent, and assign a c-number function in phase space to it. We propose to begin with a higher level of abstraction, in which the independence and the symmetric role of q and p is maintained throughout, and at once arrive at phase space state functions. Upon reduction to the q- or p-space the proposed formalism gives the conventional quantum mechanics, however, with a definite rule for ordering of factors of noncommuting observables. Further conceptual and practical merits of the formalism are demonstrated throughout the text.
Review: Semiconductor Quantum Light Sources
Andrew J Shields
2007-04-03T23:59:59.000Z
Lasers and LEDs display a statistical distribution in the number of photons emitted in a given time interval. New applications exploiting the quantum properties of light require sources for which either individual photons, or pairs, are generated in a regulated stream. Here we review recent research on single-photon sources based on the emission of a single semiconductor quantum dot. In just a few years remarkable progress has been made in generating indistinguishable single-photons and entangled photon pairs using such structures. It suggests it may be possible to realise compact, robust, LED-like semiconductor devices for quantum light generation.
R. Tsekov
2012-12-05T23:59:59.000Z
The Brownian motion of a light quantum particle in a heavy classical gas is theoretically described and a new expression for the friction coefficient is obtained for arbitrary temperature. At zero temperature it equals to the de Broglie momentum of the mean free path divided by the mean free path. Alternatively, the corresponding mobility of the quantum particle in the classical gas is equal to the square of the mean free path divided by the Planck constant. The Brownian motion of a quantum particle in a quantum environment is also discussed.
Absolute Maximal Entanglement and Quantum Secret Sharing
Helwig, Wolfram; Riera, Arnau; Latorre, José I; Lo, Hoi-Kwong
2012-01-01T23:59:59.000Z
We study the existence of absolutely maximally entangled (AME) states in quantum mechanics and its applications to quantum information. AME states are characterized by being maximally entangled for all bipartitions of the system and exhibit genuine multipartite entanglement. With such states, we present a novel parallel teleportation protocol which teleports multiple quantum states between groups of senders and receivers. The notable features of this protocol are that (i) the partition into senders and receivers can be chosen after the state has been distributed, and (ii) one group has to perform joint quantum operations while the parties of the other group only have to act locally on their system. We also prove the equivalence between pure state quantum secret sharing schemes and AME states with an even number of parties. This equivalence implies the existence of AME states for an arbitrary number of parties based on known results about the existence of quantum secret sharing schemes.
Weedbrook, Christian
The science of quantum information has arisen over the last two decades centered on the manipulation of individual quanta of information, known as quantum bits or qubits. Quantum computers, quantum cryptography, and quantum ...
Quantum Dynamical Model for Wave Function Reduction in Classical and Macroscopic Limits
Chang-Pu Sun
1993-03-22T23:59:59.000Z
In this papper, a quantum dynamical model describing the quantum measurement process is presented as an extensive generalization of the Coleman-Hepp model. In both the classical limit with very large quantum number and macroscopic limit with very large particle number in measuring instrument, this model generally realizes the wave packet collapse in quantum measurement as a consequence of the Schrodinger time evolution in either the exactly-solvable case or the non-(exactly-)solvable case. For the latter, its quasi-adiabatic case is explicitly analysed by making use of the high-order adiabatic approximation method and then manifests the wave packet collapse as well as the exactly-solvable case. By highlighting these analysis, it is finally found that an essence of the dynamical model of wave packet collapse is the factorization of the Schrodinger evolution other than the exact solvability. So many dynamical models including the well-known ones before, which are exactly-solvable or not, can be shown only to be the concrete realizations of this factorizability
Remote quantum gates mediated by spin chains
R. Ronke; I. D'Amico; T. P. Spiller
2010-03-09T23:59:59.000Z
There has been much recent study on the application of spin chains to quantum state transfer and communication. Here we demonstrate that spin chains set up for perfect quantum state transfer can be utilised to generate remote quantum gates, between spin qubits injected at the ends of the chain. The natural evolution of the system across different excitation number sectors generates a maximally-entangling and universal gate between the injected qubits, independent of the length of the chain.
Black holes are almost optimal quantum cloners
C. Adami; G. Ver Steeg
2015-04-15T23:59:59.000Z
If black holes were able to clone quantum states, a number of paradoxes in black hole physics would disappear. However, the linearity of quantum mechanics forbids exact cloning of quantum states. Here we show that black holes indeed clone incoming quantum states with a fidelity that depends on the black hole's absorption coefficient, without violating the no-cloning theorem because the clones are only approximate. Perfectly reflecting black holes are optimal universal "quantum cloning machines" and operate on the principle of stimulated emission, exactly as their quantum optical counterparts. In the limit of perfect absorption, the fidelity of clones is equal to what can be obtained via quantum state estimation methods. But for any absorption probability less than one, the cloning fidelity is nearly optimal as long as $\\omega/T\\geq10$, a common parameter for modest-sized black holes.
Amplification, Redundancy, and the Quantum Chernoff Information
Michael Zwolak; C. Jess Riedel; Wojciech H. Zurek
2014-04-12T23:59:59.000Z
Amplification was regarded, since the early days of quantum theory, as a mysterious ingredient that endows quantum microstates with macroscopic consequences, key to the "collapse of the wavepacket", and a way to avoid embarrassing problems exemplified by Schr\\"odinger's cat. Such a bridge between the quantum microworld and the classical world of our experience was postulated ad hoc in the Copenhagen Interpretation. Quantum Darwinism views amplification as replication, in many copies, of the information about quantum states. We show that such amplification is a natural consequence of a broad class of models of decoherence, including the photon environment we use to obtain most of our information. This leads to objective reality via the presence of robust and widely accessible records of selected quantum states. The resulting redundancy (the number of copies deposited in the environment) follows from the Quantum Chernoff Information that quantifies the information transmitted by a typical elementary subsystem of the environment.
Shanguang Tan
2007-04-23T23:59:59.000Z
A new kind of numbers called Hyper Space Complex Numbers and its algebras are defined and proved. It is with good properties as the classic Complex Numbers, such as expressed in coordinates, triangular and exponent forms and following the associative and commutative laws of addition and multiplication. So the classic Complex Number is developed from in complex plane with two dimensions to in complex space with N dimensions and the number system is enlarged also.
Precise energy eigenvalues of hydrogen-like ion moving in quantum plasmas
Dutta, S; Mukherjee, T K
2014-01-01T23:59:59.000Z
The analytic form of the electrostatic potential felt by a slowly moving test charge in quantum plasma is being derived. It has been shown that the potential composed of two parts: Debye-Huckel screening term and near-field wake potential which depends on the velocity of the test charge and the number density of the plasma electrons. Rayleigh-Ritz variational calculation has been done to estimate precise energy eigenvalues of hydrogen-like ion under such plasma environment. A detailed analysis shows that the energy levels are gradually moves to the continuum with increasing plasma electron density while level crossing phenomenon have been observed with the variation of ion velocity.
Some Physics And System Issues In The Security Analysis Of Quantum Key Distribution Protocols
Horace P. Yuen
2014-05-07T23:59:59.000Z
In this paper we review a number of issues on the security of quantum key distribution (QKD) protocols that bear directly on the relevant physics or mathematical representation of the QKD cryptosystem. It is shown that the cryptosystem representation itself may miss out many possible attacks which are not accounted for in the security analysis and proofs. Hence the final security claims drawn from such analysis are not reliable, apart from foundational issues about the security criteria that are discussed elsewhere. The cases of continuous-variable QKD and multi-photon sources are elaborated upon.
Entropy of quantum channel in the theory of quantum information
Wojciech Roga
2011-10-03T23:59:59.000Z
Quantum channels, also called quantum operations, are linear, trace preserving and completely positive transformations in the space of quantum states. Such operations describe discrete time evolution of an open quantum system interacting with an environment. The thesis contains an analysis of properties of quantum channels and different entropies used to quantify the decoherence introduced into the system by a given operation. Part I of the thesis provides a general introduction to the subject. In Part II, the action of a quantum channel is treated as a process of preparation of a quantum ensemble. The Holevo information associated with this ensemble is shown to be bounded by the entropy exchanged during the preparation process between the initial state and the environment. A relation between the Holevo information and the entropy of an auxiliary matrix consisting of square root fidelities between the elements of the ensemble is proved in some special cases. Weaker bounds on the Holevo information are also established. The entropy of a channel, also called the map entropy, is defined as the entropy of the state corresponding to the channel by the Jamiolkowski isomorphism. In Part III of the thesis, the additivity of the entropy of a channel is proved. The minimal output entropy, which is difficult to compute, is estimated by an entropy of a channel which is much easier to obtain. A class of quantum channels is specified, for which additivity of channel capacity is conjectured. The last part of the thesis contains characterization of Davies channels, which correspond to an interaction of a state with a thermal reservoir in the week coupling limit, under the condition of quantum detailed balance and independence of rotational and dissipative evolutions. The Davies channels are characterized for one-qubit and one-qutrit systems.
On the group theoretic structure of a class of quantum dialogue protocols
Chitra Shukla; Vivek Kothari; Anindita Banerjee; Anirban Pathak
2012-03-27T23:59:59.000Z
Intrinsic symmetry of the existing protocols of quantum dialogue are explored. It is shown that if we have a set of mutually orthogonal $n$-qubit states {\
Lloyd, S.
1992-01-01T23:59:59.000Z
Digital computers are machines that can be programmed to perform logical and arithmetical operations. Contemporary digital computers are universal,'' in the sense that a program that runs on one computer can, if properly compiled, run on any other computer that has access to enough memory space and time. Any one universal computer can simulate the operation of any other; and the set of tasks that any such machine can perform is common to all universal machines. Since Bennett's discovery that computation can be carried out in a non-dissipative fashion, a number of Hamiltonian quantum-mechanical systems have been proposed whose time-evolutions over discrete intervals are equivalent to those of specific universal computers. The first quantum-mechanical treatment of computers was given by Benioff, who exhibited a Hamiltonian system with a basis whose members corresponded to the logical states of a Turing machine. In order to make the Hamiltonian local, in the sense that its structure depended only on the part of the computation being performed at that time, Benioff found it necessary to make the Hamiltonian time-dependent. Feynman discovered a way to make the computational Hamiltonian both local and time-independent by incorporating the direction of computation in the initial condition. In Feynman's quantum computer, the program is a carefully prepared wave packet that propagates through different computational states. Deutsch presented a quantum computer that exploits the possibility of existing in a superposition of computational states to perform tasks that a classical computer cannot, such as generating purely random numbers, and carrying out superpositions of computations as a method of parallel processing. In this paper, we show that such computers, by virtue of their common function, possess a common form for their quantum dynamics.
Lloyd, S.
1992-12-01T23:59:59.000Z
Digital computers are machines that can be programmed to perform logical and arithmetical operations. Contemporary digital computers are ``universal,`` in the sense that a program that runs on one computer can, if properly compiled, run on any other computer that has access to enough memory space and time. Any one universal computer can simulate the operation of any other; and the set of tasks that any such machine can perform is common to all universal machines. Since Bennett`s discovery that computation can be carried out in a non-dissipative fashion, a number of Hamiltonian quantum-mechanical systems have been proposed whose time-evolutions over discrete intervals are equivalent to those of specific universal computers. The first quantum-mechanical treatment of computers was given by Benioff, who exhibited a Hamiltonian system with a basis whose members corresponded to the logical states of a Turing machine. In order to make the Hamiltonian local, in the sense that its structure depended only on the part of the computation being performed at that time, Benioff found it necessary to make the Hamiltonian time-dependent. Feynman discovered a way to make the computational Hamiltonian both local and time-independent by incorporating the direction of computation in the initial condition. In Feynman`s quantum computer, the program is a carefully prepared wave packet that propagates through different computational states. Deutsch presented a quantum computer that exploits the possibility of existing in a superposition of computational states to perform tasks that a classical computer cannot, such as generating purely random numbers, and carrying out superpositions of computations as a method of parallel processing. In this paper, we show that such computers, by virtue of their common function, possess a common form for their quantum dynamics.
Quantum Cherenkov radiation and noncontact friction
Golestanian, Ramin
We present a number of arguments to demonstrate that a quantum analog of the Cherenkov effect occurs when two nondispersive half spaces are in relative motion. We show that they experience friction beyond a threshold ...
Probabilistic model of fault detection in quantum circuits
Anindita Banerjee; Anirban Pathak
2009-05-12T23:59:59.000Z
It is shown that the fault testing for quantum circuits does not follow conventional classical techniques. If probabilistic gate like Hadamard gate is included in a circuit then the classical notion of test vector is shown to fail. We have reported several new and distinguishing features of quantum fault and also presented a general methodology for detection of functional faults in a quantum circuit. The technique can generate test vectors for detection of different kinds of fault. Specific examples are given and time complexity of the proposed quantum fault detection algorithm is reported.
Flexible quantum private queries based on quantum key distribution
Fei Gao; Bin Liu; Qiao-Yan Wen; Hui Chen
2011-11-07T23:59:59.000Z
We present a flexible quantum-key-distribution-based protocol for quantum private queries. Similar to M. Jakobi et al's protocol [Phys. Rev. A 83, 022301 (2011)], it is loss tolerant, practical and robust against quantum memory attack. Furthermore, our protocol is more flexible and controllable. We show that, by adjusting the value of $\\theta$, the average number of the key bits Alice obtains can be located on any fixed value the users wanted for any database size. And the parameter $k$ is generally smaller (even $k=1$ can be achieved) when $\\theta<\\pi/4$, which implies lower complexity of both quantum and classical communications. Furthermore, the users can choose a smaller $\\theta$ to get better database security, or a larger $\\theta$ to obtain a lower probability with which Bob can correctly guess the address of Alice's query.
Quantum Internal Model Principle: Decoherence Control
Narayan Ganesan; Tzyh-Jong Tarn
2010-12-10T23:59:59.000Z
In this article, we study the problem of designing a Decoherence Control for quantum systems with the help of a scalable ancillary quantum control and techniques from geometric control theory, in order to successfully and completely decouple an open quantum system from its environment. We re-formulate the problem of decoherence control as a disturbance rejection scheme which also leads us to the idea of Internal Model Principle for quantum control systems which is first of its kind in the literature. It is shown that decoupling a quantum disturbance from an open quantum system, is possible only with the help of a quantum controller which takes into account the model of the environmental interaction. This is demonstrated for a simple 2-qubit system wherein the effects of decoherence are completely eliminated. The theory provides conditions to be imposed on the controller to ensure perfect decoupling. Hence the problem of decoherence control naturally gives rise to the quantum internal model principle which relates the disturbance rejecting control to the model of the environmental interaction. Classical internal model principle and disturbance decoupling focus on different aspects viz. perfect output tracking and complete decoupling of output from external disturbances respectively. However for quantum systems, the two problems come together and merge in order to produce an effective platform for decoherence control. In this article we introduce a seminal connection between disturbance decoupling and the corresponding analog for internal model principle for quantum systems.
Classical Resonances and Quantum Scarring
Christopher Manderfeld
2003-01-22T23:59:59.000Z
We study the correspondence between phase-space localization of quantum (quasi-)energy eigenstates and classical correlation decay, given by Ruelle-Pollicott resonances of the Frobenius-Perron operator. It will be shown that scarred (quasi-)energy eigenstates are correlated: Pairs of eigenstates strongly overlap in phase space (scar in same phase-space regions) if the difference of their eigenenergies is close to the phase of a leading classical resonance. Phase-space localization of quantum states will be measured by $L^2$ norms of their Husimi functions.
Quantum discord determines the interferometric power of quantum states
Davide Girolami; Alexandre M. Souza; Vittorio Giovannetti; Tommaso Tufarelli; Jefferson G. Filgueiras; Roberto S. Sarthour; Diogo O. Soares-Pinto; Ivan S. Oliveira; Gerardo Adesso
2014-05-28T23:59:59.000Z
Quantum metrology exploits quantum mechanical laws to improve the precision in estimating technologically relevant parameters such as phase, frequency, or magnetic fields. Probe states are usually tailored on the particular dynamics whose parameters are being estimated. Here we consider a novel framework where quantum estimation is performed in an interferometric configuration, using bipartite probe states prepared when only the spectrum of the generating Hamiltonian is known. We introduce a figure of merit for the scheme, given by the worst case precision over all suitable Hamiltonians, and prove that it amounts exactly to a computable measure of discord-type quantum correlations for the input probe. We complement our theoretical results with a metrology experiment, realized in a highly controllable room-temperature nuclear magnetic resonance setup, which provides a proof-of-concept demonstration for the usefulness of discord in sensing applications. Discordant probes are shown to guarantee a nonzero precision in the estimation procedure for different generating Hamiltonians, while classically correlated probes are unable to accomplish the estimation in a worst case setting. This work establishes a rigorous and direct operational interpretation for general quantum correlations, shedding light on their potential for quantum technology.
Contextuality supplies the magic for quantum computation
Mark Howard; Joel J. Wallman; Victor Veitch; Joseph Emerson
2014-10-15T23:59:59.000Z
Quantum computers promise dramatic advantages over their classical counterparts, but the answer to the most basic question "What is the source of the power in quantum computing?" has remained elusive. Here we prove a remarkable equivalence between the onset of contextuality and the possibility of universal quantum computation via magic state distillation. This is a conceptually satisfying link because contextuality provides one of the fundamental characterizations of uniquely quantum phenomena and, moreover, magic state distillation is the leading model for experimentally realizing fault-tolerant quantum computation. Furthermore, this connection suggests a unifying paradigm for the resources of quantum information: the nonlocality of quantum theory is a particular kind of contextuality and nonlocality is already known to be a critical resource for achieving advantages with quantum communication. In addition to clarifying these fundamental issues, this work advances the resource framework for quantum computation, which has a number of practical applications, such as characterizing the efficiency and trade-offs between distinct theoretical and experimental schemes for achieving robust quantum computation and bounding the overhead cost for the classical simulation of quantum algorithms.
Strongly Intensive Measures for Particle Number Fluctuations: Effects of Hadronic Resonances
Viktor V. Begun; Mark I. Gorenstein; Katarzyna Grebieszkow
2015-05-15T23:59:59.000Z
Strongly intensive measures $\\Delta$ and $\\Sigma$ are used to study event-by-event fluctuations of hadron multiplicities in nucleus-nucleus collisions. The effects of resonance decays are investigated within statistical model and relativistic transport model. Two specific examples are considered: resonance decays to two positively charged particles (e.g., $\\Delta^{++}\\rightarrow p+ \\pi^+$) and to $\\pi^+\\pi^-$-pairs. (e.g., $\\rho^0\\rightarrow \\pi^-+\\pi^+$). It is shown that resonance abundances at the chemical freeze-out can be estimated by measuring the fluctuations of the number of stable hadrons. These model results are compared to the full hadron-resonance gas analysis within both the grand canonical and canonical ensemble. The ultra-relativistic quantum molecular dynamics (UrQMD) model of nucleus-nucleus collisions is used to illustrate the role of global charge conservation, centrality selection, and limited experimental acceptance.
Bernd Fröhlich; James F. Dynes; Marco Lucamarini; Andrew W. Sharpe; Zhiliang Yuan; Andrew J. Shields
2014-09-02T23:59:59.000Z
The theoretically proven security of quantum key distribution (QKD) could revolutionise how information exchange is protected in the future. Several field tests of QKD have proven it to be a reliable technology for cryptographic key exchange and have demonstrated nodal networks of point-to-point links. However, so far no convincing answer has been given to the question of how to extend the scope of QKD beyond niche applications in dedicated high security networks. Here we show that adopting simple and cost-effective telecommunication technologies to form a quantum access network can greatly expand the number of users in quantum networks and therefore vastly broaden their appeal. We are able to demonstrate that a high-speed single-photon detector positioned at a network node can be shared between up to 64 users for exchanging secret keys with the node, thereby significantly reducing the hardware requirements for each user added to the network. This point-to-multipoint architecture removes one of the main obstacles restricting the widespread application of QKD. It presents a viable method for realising multi-user QKD networks with resource efficiency and brings QKD closer to becoming the first widespread technology based on quantum physics.
Blue sky in SOI: new opportunities for quantum and hot-electron devices
Luryi, Serge
Blue sky in SOI: new opportunities for quantum and hot-electron devices S. Luryi a , A. Zaslavsky b to quantum effect and hot-electron devices. A number of such devices, based on quantum tunneling, hot-electron) substrates with ultrathin Si and insulator layers opens new oppor- tunities for quantum effect and hot-electron
Measurement-driven quantum evolution
Roa, L.; Delgado, A.; Ladron de Guevara, M. L.; Klimov, A. B. [Center for Quantum Optics and Quantum Information, Departamento de Fisica, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile); Departamento de Fisica, Universidad Catolica del Norte, Casilla 1280, Antofagasta, Chile and Center for Quantum Optics and Quantum Information, Departamento de Fisica, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile); Departamento de Fisica, Universidad de Guadalajara, Revolucion 1500, 44420 Guadalajara, Jalisco (Mexico)
2006-01-15T23:59:59.000Z
We study the problem of mapping an unknown mixed quantum state onto a known pure state without the use of unitary transformations. This is achieved with the help of sequential measurements of two noncommuting observables only. We show that the overall success probability is maximized in the case of measuring two observables whose eigenstates define mutually unbiased bases. We find that for this optimal case the success probability quickly converges to unity as the number of measurement processes increases and that it is almost independent of the initial state. In particular, we show that to guarantee a success probability close to one the number of consecutive measurements must be larger than the dimension of the Hilbert space. We connect these results to quantum copying, quantum deleting, and entanglement generation.
Conditional quantum distinguishability and pure quantum communication
Tian-Hai Zeng
2005-09-14T23:59:59.000Z
I design a simple way of distinguishing non-orthogonal quantum states with perfect reliability using only quantum control-not gates in one condition. In this way, we can implement pure quantum communication in directly sending classical information, Ekert quantum cryptography and quantum teleportation without the help of classical communications channel.
Generic Quantum Ratchet Accelerator with Full Classical Chaos
Jiangbin Gong; Paul Brumer
2006-09-05T23:59:59.000Z
A simple model of quantum ratchet transport that can generate unbounded linear acceleration of the quantum ratchet current is proposed, with the underlying classical dynamics fully chaotic. The results demonstrate that generic acceleration of quantum ratchet transport can occur with any type of classical phase space structure. The quantum ratchet transport with full classical chaos is also shown to be very robust to noise due to the large linear acceleration afforded by the quantum dynamics. One possible experiment allowing observation of these predictions is suggested.
Device-Independent Verifiable Blind Quantum Computation
Michal Hajdušek; Carlos A. Pérez-Delgado; Joseph F. Fitzsimons
2015-02-09T23:59:59.000Z
As progress on experimental quantum processors continues to advance, the problem of verifying the correct operation of such devices is becoming a pressing concern. Although recent progress has resulted in several protocols which can verify the output of a quantum computation performed by entangled but non-communicating processors, the overhead for such schemes is prohibitive, scaling at least as the 22nd power of the number of gates. We present a new approach based on a combination of verified blind quantum computation and Bell state self-testing. This approach has significantly reduced overhead, with resources scaling as a quartic polynomial in the number of gates.
A Review of Procedure to Evolve Quantum Procedures
Adrian Gepp; Phil Stocks
2007-08-24T23:59:59.000Z
There exist quantum algorithms that are more efficient than their classical counterparts; such algorithms were invented by Shor in 1994 and then Grover in 1996. A lack of invention since Grover's algorithm has been commonly attributed to the non-intuitive nature of quantum algorithms to the classically trained person. Thus, the idea of using computers to automatically generate quantum algorithms based on an evolutionary model emerged. A limitation of this approach is that quantum computers do not yet exist and quantum simulation on a classical machine has an exponential order overhead. Nevertheless, early research into evolving quantum algorithms has shown promise. This paper provides an introduction into quantum and evolutionary algorithms for the computer scientist not familiar with these fields. The exciting field of using evolutionary algorithms to evolve quantum algorithms is then reviewed.
How detrimental is decoherence in adiabatic quantum computation?
Albash, Tameem
2015-01-01T23:59:59.000Z
Recent experiments with increasingly larger numbers of qubits have sparked renewed interest in adiabatic quantum computation, and in particular quantum annealing. A central question that is repeatedly asked is whether quantum features of the evolution can survive over the long time-scales used for quantum annealing relative to standard measures of the decoherence time. We reconsider the role of decoherence in adiabatic quantum computation and quantum annealing using the adiabatic quantum master equation formalism. We restrict ourselves to the weak-coupling and singular-coupling limits, which correspond to decoherence in the energy eigenbasis and in the computational basis, respectively. We demonstrate that decoherence in the instantaneous energy eigenbasis does not necessarily detrimentally affect adiabatic quantum computation, and in particular that a short single-qubit $T_2$ time need not imply adverse consequences for the success of the quantum adiabatic algorithm. We further demonstrate that boundary canc...
Finite size scaling for quantum criticality using the finite-element method
Edwin Antillon; Birgit Wehefritz-Kaufmann; Sabre Kais
2012-03-08T23:59:59.000Z
Finite size scaling for the Schr\\"{o}dinger equation is a systematic approach to calculate the quantum critical parameters for a given Hamiltonian. This approach has been shown to give very accurate results for critical parameters by using a systematic expansion with global basis-type functions. Recently, the finite element method was shown to be a powerful numerical method for ab initio electronic structure calculations with a variable real-space resolution. In this work, we demonstrate how to obtain quantum critical parameters by combining the finite element method (FEM) with finite size scaling (FSS) using different ab initio approximations and exact formulations. The critical parameters could be atomic nuclear charges, internuclear distances, electron density, disorder, lattice structure, and external fields for stability of atomic, molecular systems and quantum phase transitions of extended systems. To illustrate the effectiveness of this approach we provide detailed calculations of applying FEM to approximate solutions for the two-electron atom with varying nuclear charge; these include Hartree-Fock, density functional theory under the local density approximation, and an "exact"' formulation using FEM. We then use the FSS approach to determine its critical nuclear charge for stability; here, the size of the system is related to the number of elements used in the calculations. Results prove to be in good agreement with previous Slater-basis set calculations and demonstrate that it is possible to combine finite size scaling with the finite-element method by using ab initio calculations to obtain quantum critical parameters. The combined approach provides a promising first-principles approach to describe quantum phase transitions for materials and extended systems.
Liang, Min
2012-01-01T23:59:59.000Z
Public-key cryptosystems for quantum messages are considered from two aspects: public-key encryption and public-key authentication. Firstly, we propose a general construction of quantum public-key encryption scheme, and then construct an information-theoretic secure instance. Then, we propose a quantum public-key authentication scheme, which can protect the integrity of quantum messages. This scheme can both encrypt and authenticate quantum messages. It is information-theoretic secure with regard to encryption, and the success probability of tampering decreases exponentially with the security parameter with regard to authentication. Compared with classical public-key cryptosystems, one private-key in our schemes corresponds to an exponential number of public-keys, and every quantum public-key used by the sender is an unknown quantum state to the sender.
Min Liang; Li Yang
2012-05-10T23:59:59.000Z
Public-key cryptosystems for quantum messages are considered from two aspects: public-key encryption and public-key authentication. Firstly, we propose a general construction of quantum public-key encryption scheme, and then construct an information-theoretic secure instance. Then, we propose a quantum public-key authentication scheme, which can protect the integrity of quantum messages. This scheme can both encrypt and authenticate quantum messages. It is information-theoretic secure with regard to encryption, and the success probability of tampering decreases exponentially with the security parameter with regard to authentication. Compared with classical public-key cryptosystems, one private-key in our schemes corresponds to an exponential number of public-keys, and every quantum public-key used by the sender is an unknown quantum state to the sender.
Adan Cabello; Lars Eirik Danielsen; Antonio J. Lopez-Tarrida; Jose R. Portillo
2012-07-15T23:59:59.000Z
We introduce a physical approach to social networks (SNs) in which each actor is characterized by a yes-no test on a physical system. This allows us to consider SNs beyond those originated by interactions based on pre-existing properties, as in a classical SN (CSN). As an example of SNs beyond CSNs, we introduce quantum SNs (QSNs) in which actor is characterized by a test of whether or not the system is in a quantum state. We show that QSNs outperform CSNs for a certain task and some graphs. We identify the simplest of these graphs and show that graphs in which QSNs outperform CSNs are increasingly frequent as the number of vertices increases. We also discuss more general SNs and identify the simplest graphs in which QSNs cannot be outperformed.
Sandia Energy - Quantum Optics
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
Quantum Optics Home Energy Research EFRCs Solid-State Lighting Science EFRC Quantum Optics Quantum OpticsTara Camacho-Lopez2015-03-30T16:37:03+00:00 Quantum Optics with a Single...
Quadratic control of quantum processes
Luigi Accardi; Andreas Boukas
2013-08-07T23:59:59.000Z
Within the framework of the Accardi-Fagnola-Quaegebeur (AFQ) representation free calculus of \\cite{b}, we consider the problem of controlling the size of a quantum stochastic flow generated by a unitary stochastic evolution affected by quantum noise. In the case when the evolution is driven by first order white noise (which includes quantum Brownian motion) the control is shown to be given in terms of the solution of an algebraic Riccati equation. This is done by first solving the problem of controlling (by minimizing an associated quadratic performance criterion) a stochastic process whose evolution is described by a stochastic differential equation of the type considerd in \\cite{b}. The solution is given as a feedback control law in terms of the solution of a stochastic Riccati equation.
Curvature and Tachibana numbers
Stepanov, Sergey E [Finance Academy under the Government of the Russian Federation, Moscow (Russian Federation)
2011-07-31T23:59:59.000Z
The aim of this paper is to define the rth Tachibana number t{sub r} of an n-dimensional compact oriented Riemannian manifold as the dimension of the space of conformally Killing r-forms, for r=1,2,...,n-1. We also describe properties of these numbers, by analogy with properties of the Betti numbers b{sub r} of a compact oriented Riemannian manifold. Bibliography: 25 titles.
Study of field driven electroluminescence in colloidal quantum dot solids
Bozyigit, Deniz
Semiconductor nanocrystals, or quantum dots(QDs), promise to drive advances in electronic light generation. It was recently shown that long range transport of charge, which is typically required for electric excitation and ...
Rosen, Jacob
" by H. Kim, L. M. Miller, I. Fedulow, M. Simkins, G. M. Abrams, N. Byl, and J. Rosen on p. 153. #12;IEEE
Thermo-quantum diffusion in periodic potentials
R. Tsekov
2012-01-18T23:59:59.000Z
Quantum Brownian motion in a periodic cosine potential is studied and a simple estimate of the tunneling effect is obtained in the frames of a quasi-equilibrium semiclassical approach. It is shown that the latter is applicable for heavy particles but electrons cannot be described properly since the quantum effects dominate over the thermal ones. The purely quantum electron diffusion is investigated at zero temperature and demonstrates that electrons do not obey the classical Einstein law of Brownian motion in the field of periodic potentials, since the dispersion of the wave packet increases logarithmically in time.
Schrödinger group and quantum finance
Juan M. Romero; Ulises Lavana; Elio Martínez
2013-04-18T23:59:59.000Z
Using the one dimensional free particle symmetries, the quantum finance symmetries are obtained. Namely, it is shown that Black-Scholes equation is invariant under Schr\\"odinger group. In order to do this, the one dimensional free non-relativistic particle and its symmetries are revisited. To get the Black-Scholes equation symmetries, the particle mass is identified as the inverse of square of the volatility. Furthermore, using financial variables, a Schr\\"odinger algebra representation is constructed.
Nuclear quantum effects in water
Joseph A. Morrone; Roberto Car
2008-03-25T23:59:59.000Z
In this work, a path integral Car-Parrinello molecular dynamics simulation of liquid water is performed. It is found that the inclusion of nuclear quantum effects systematically improves the agreement of first principles simulations of liquid water with experiment. In addition, the proton momentum distribution is computed utilizing a recently developed open path integral molecular dynamics methodology. It is shown that these results are in good agreement with neutron Compton scattering data for liquid water and ice.
Joint probabilities and quantum cognition
Acacio de Barros, J. [Liberal Studies, 1600 Holloway Ave., San Francisco State University, San Francisco, CA 94132 (United States)
2012-12-18T23:59:59.000Z
In this paper we discuss the existence of joint probability distributions for quantumlike response computations in the brain. We do so by focusing on a contextual neural-oscillator model shown to reproduce the main features of behavioral stimulus-response theory. We then exhibit a simple example of contextual random variables not having a joint probability distribution, and describe how such variables can be obtained from neural oscillators, but not from a quantum observable algebra.
An additive Hamiltonian plus Landauer's Principle yields quantum theory
Chris Fields
2015-03-27T23:59:59.000Z
It is shown that no-signalling, a quantum of action, unitarity, detailed balance, Bell's theorem, the Hilbert-space representation of physical states and the Born rule all follow from the assumption of an additive Hamiltonian together with Landauer's principle. Common statements of the "classical limit" of quantum theory, as well as common assumptions made by "interpretations" of quantum theory, contradict additivity, Landauer's principle, or both.
Tunneling through high energy barriers in simulated quantum annealing
Elizabeth Crosson; Mingkai Deng
2014-10-30T23:59:59.000Z
We analyze the performance of simulated quantum annealing (SQA) on an optimization problem for which simulated classical annealing (SA) is provably inefficient because of a high energy barrier. We present evidence that SQA can pass through this barrier to find the global minimum efficiently. This demonstrates the potential for SQA to inherit some of the advantages of quantum annealing (QA), since this problem has been previously shown to be efficiently solvable by quantum adiabatic optimization.
Behmer, Spencer T.
Definitions Â· Numbered Space Â a single space marked with a number and reserved for a single permit 24/7 Â· Unnumbered Space Â a space which can be used by any customer allowed to park in that lot. High Low Average Question 4: If I buy a staff permit for an UNNUMBERED* space in a non-gated surface
Stochastic quantization weakening and quantum entanglement decoherence
Piero Chiarelli
2014-12-23T23:59:59.000Z
The paper investigates the non-local property of quantum mechanics in the quantum hydrodynamic analogy (QHA) given by Madelung. The role of the quantum potential in generating the non-local dynamics of quantum mechanics is analyzed. The work shows how in presence of noise the non-local properties as well as the quantization of the action are perturbed. The resulting stochastic QHA dynamics much depend by the strength of the interaction: Strongly bounded systems (such as linear ones) lead to quantum entangled stochastic behavior, while weakly bounded ones may be not able to maintain the quantum superposition of states on large distances and may loose their macro-scale quantum coherence acquiring the classical stochastic evolution . The work shows that in the frame of the stochastic approach it is possible to have freedom between quantum weakly bounded systems. The stochastic QHA model shows that the wave-function collapse to an eigenstates (deriving by interaction of a quantum microscopic system with a classical (macroscopic) one) can be described by the model itself as a kinetic quantum (relaxation) process to a stationary state. Since the time of the wave function decay to the eigenstate represents the minimum duration time of a measurement, the minimum uncertainty principle is shown to be compatible with the relativistic postulate about the light speed as the maximum velocity of transmission of interaction. About this topic, the paper shows that the Lorenz invariance of the relativistic quantum potential (coming from the Dirac equation) enforces the hypothesis that the superluminal transmission of information are not present in measurements on quantum entangled state.
Kockelman, Kara M.
of Contents shown here), and its graphics are disfigured. These problems are due to the document's original standards throughout urban areas. These results also represent a step forward in the inclusion of measures
Low Energy Quantum System Simulation
Peter Cho; Karl Berggren
2003-10-26T23:59:59.000Z
A numerical method for solving Schrodinger's equation based upon a Baker-Campbell-Hausdorff (BCH) expansion of the time evolution operator is presented herein. The technique manifestly preserves wavefunction norm, and it can be applied to problems in any number of spatial dimensions. We also identify a particular dimensionless ratio of potential to kinetic energies as a key coupling constant. This coupling establishes characteristic length and time scales for a large class of low energy quantum states, and it guides the choice of step sizes in numerical work. Using the BCH method in conjunction with an imaginary time rotation, we compute low energy eigenstates for several quantum systems coupled to non-trivial background potentials. The approach is subsequently applied to the study of 1D propagating wave packets and 2D bound state time development. Failures of classical expectations uncovered by simulations of these simple systems help develop quantum intuition. Finally, we investigate the response of a Superconducting Quantum Interference Device (SQUID) to a time dependent potential. We discuss how to engineer the potential's energy and time scales so that the SQUID acts as a quantum NOT gate. The notional simulation we present for this gate provides useful insight into the design of one candidate building block for a quantum computer.
Photonic quantum walk in a single beam with twisted light
Cardano, Filippo; Karimi, Ebrahim; Slussarenko, Sergei; Paparo, Domenico; de Lisio, Corrado; Sciarrino, Fabio; Santamato, Enrico; Marrucci, Lorenzo
2014-01-01T23:59:59.000Z
Inspired by the classical phenomenon of random walk, the concept of quantum walk has emerged recently as a powerful platform for the dynamical simulation of complex quantum systems, entanglement production and universal quantum computation. Such a wide perspective motivates a renewing search for efficient, scalable and stable implementations of this quantum process. Photonic approaches have hitherto mainly focused on multi-path schemes, requiring interferometric stability and a number of optical elements that scales quadratically with the number of steps. Here we report the experimental realization of a quantum walk taking place in the orbital angular momentum space of light, both for a single photon and for two simultaneous indistinguishable photons. The whole process develops in a single light beam, with no need of interferometers, and requires optical resources scaling linearly with the number of steps. Our demonstration introduces a novel versatile photonic platform for implementing quantum simulations, b...
Nonlinear quantum input-output analysis using Volterra series
Jing Zhang; Yu-xi Liu; Re-Bing Wu; Kurt Jacobs; Sahin Kaya Ozdemir; Lan Yang; Tzyh-Jong Tarn; Franco Nori
2014-08-04T23:59:59.000Z
Quantum input-output theory plays a very important role for analyzing the dynamics of quantum systems, especially large-scale quantum networks. As an extension of the input-output formalism of Gardiner and Collet, we develop a new approach based on the quantum version of the Volterra series which can be used to analyze nonlinear quantum input-output dynamics. By this approach, we can ignore the internal dynamics of the quantum input-output system and represent the system dynamics by a series of kernel functions. This approach has the great advantage of modelling weak-nonlinear quantum networks. In our approach, the number of parameters, represented by the kernel functions, used to describe the input-output response of a weak-nonlinear quantum network, increases linearly with the scale of the quantum network, not exponentially as usual. Additionally, our approach can be used to formulate the quantum network with both nonlinear and nonconservative components, e.g., quantum amplifiers, which cannot be modelled by the existing methods, such as the Hudson-Parthasarathy model and the quantum transfer function model. We apply our general method to several examples, including Kerr cavities, optomechanical transducers, and a particular coherent feedback system with a nonlinear component and a quantum amplifier in the feedback loop. This approach provides a powerful way to the modelling and control of nonlinear quantum networks.
Paola Zizzi; Eliano Pessa; Fabio Cardone
2010-06-05T23:59:59.000Z
We consider the theoretical setting of a superfluid like 3He in a rotating container, which is set between the two layers of a type-II superconductor. We describe the superfluid vortices as a 2-dimensional Ising-like model on a triangular lattice in presence of local magnetic fields. The interaction term of the superfluid vortices with the Abrikosov vortices of the superconductor appears then as a symmetry breaking term in the free energy. Such a term gives a higher probability of quantum tunnelling across the potential barrier for bubbles nucleation, thus favouring quantum cavitation.
Quantum computer of wire circuit architecture
S. A. Moiseev; F. F. Gubaidullin; S. N. Andrianov
2010-01-07T23:59:59.000Z
First solid state quantum computer was built using transmons (cooper pair boxes). The operation of the computer is limited because of using a number of the rigit cooper boxes working with fixed frequency at temperatures of superconducting material. Here, we propose a novel architecture of quantum computer based on a flexible wire circuit of many coupled quantum nodes containing controlled atomic (molecular) ensembles. We demonstrate wide opportunities of the proposed computer. Firstly, we reveal a perfect storage of external photon qubits to multi-mode quantum memory node and demonstrate a reversible exchange of the qubits between any arbitrary nodes. We found optimal parameters of atoms in the circuit and self quantum modes for quantum processing. The predicted perfect storage has been observed experimentally for microwave radiation on the lithium phthalocyaninate molecule ensemble. Then also, for the first time we show a realization of the efficient basic two-qubit gate with direct coupling of two arbitrary nodes by using appropriate atomic frequency shifts in the circuit nodes. Proposed two-qubit gate runs with a speed drastically accelerated proportionally to the number of atoms in the node. The direct coupling and accelerated two-qubit gate can be realized for large number of the circuit nodes. Finally, we describe two and three-dimensional scalable architectures that pave the road to construction of universal multi-qubit quantum computer operating at room temperatures.
Quantum Phase Space, Quantization Hierarchy, and Eclectic Quantum Many-Body System
Dong-Sheng Wang
2014-10-05T23:59:59.000Z
An operator-valued quantum phase space formula is constructed. The phase space formula of Quantum Mechanics provides a natural link between first and second quantization, thus contributing to the understanding of quantization problem. By the combination of quantization and hamiltonization of dynamics, a quantization hierarchy is introduced, beyond the framework of first and second quantization and generalizing the standard quantum theory. We apply our quantization method to quantum many-body system and propose an eclectic model, in which the dimension of Hilbert space does not scale exponentially with the number of particles due to the locality of interaction, and the evolution is a constrained Hamiltonian dynamics.
Phil Gossett
1998-08-30T23:59:59.000Z
This paper shows how to design efficient arithmetic elements out of quantum gates using "carry-save" techniques borrowed from classical computer design. This allows bit-parallel evaluation of all the arithmetic elements required for Shor's algorithm, including modular arithmetic, deferring all carry propagation until the end of the entire computation. This reduces the quantum gate delay from O(N^3) to O(N log N) at a cost of increasing the number of qubits required from O(N) to O(N^2).
Sandia National Laboratories: Quantum Optics
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
ClimateQuantum Optics Quantum Optics videobanner Quantum Optics with a Single Semiconductor Quantum Dot Speaker: Weng Chow, EFRC Scientist Date: September 14, 2011 Event:...
Quantum Holonomies for Quantum Computing
Jiannis Pachos; Paolo Zanardi
2001-03-19T23:59:59.000Z
Holonomic Quantum Computation (HQC) is an all-geometrical approach to quantum information processing. In the HQC strategy information is encoded in degenerate eigen-spaces of a parametric family of Hamiltonians. The computational network of unitary quantum gates is realized by driving adiabatically the Hamiltonian parameters along loops in a control manifold. By properly designing such loops the non-trivial curvature of the underlying bundle geometry gives rise to unitary transformations i.e., holonomies that implement the desired unitary transformations. Conditions necessary for universal QC are stated in terms of the curvature associated to the non-abelian gauge potential (connection) over the control manifold. In view of their geometrical nature the holonomic gates are robust against several kind of perturbations and imperfections. This fact along with the adiabatic fashion in which gates are performed makes in principle HQC an appealing way towards universal fault-tolerant QC.
Quantum Holonomies for Quantum Computing
Pachos, J; Pachos, Jiannis; Zanardi, Paolo
2001-01-01T23:59:59.000Z
Holonomic Quantum Computation (HQC) is an all-geometrical approach to quantum information processing. In the HQC strategy information is encoded in degenerate eigen-spaces of a parametric family of Hamiltonians. The computational network of unitary quantum gates is realized by driving adiabatically the Hamiltonian parameters along loops in a control manifold. By properly designing such loops the non-trivial curvature of the underlying bundle geometry gives rise to unitary transformations i.e., holonomies that implement the desired unitary transformations. Conditions necessary for universal QC are stated in terms of the curvature associated to the non-abelian gauge potential (connection) over the control manifold. In view of their geometrical nature the holonomic gates are robust against several kind of perturbations and imperfections. This fact along with the adiabatic fashion in which gates are performed makes in principle HQC an appealing way towards universal fault-tolerant QC.
Surface code quantum communication
Austin G. Fowler; David S. Wang; Charles D. Hill; Thaddeus D. Ladd; Rodney Van Meter; Lloyd C. L. Hollenberg
2010-02-05T23:59:59.000Z
Quantum communication typically involves a linear chain of repeater stations, each capable of reliable local quantum computation and connected to their nearest neighbors by unreliable communication links. The communication rate in existing protocols is low as two-way classical communication is used. We show that, if Bell pairs are generated between neighboring stations with a probability of heralded success greater than 0.65 and fidelity greater than 0.96, two-way classical communication can be entirely avoided and quantum information can be sent over arbitrary distances with arbitrarily low error at a rate limited only by the local gate speed. The number of qubits per repeater scales logarithmically with the communication distance. If the probability of heralded success is less than 0.65 and Bell pairs between neighboring stations with fidelity no less than 0.92 are generated only every T_B seconds, the logarithmic resource scaling remains and the communication rate through N links is proportional to 1/(T_B log^2 N).
Quantum++ - A C++11 quantum computing library
Vlad Gheorghiu
2014-12-15T23:59:59.000Z
Quantum++ is a general-purpose multi-threaded quantum computing library written in C++11 and composed solely of header files. The library is not restricted to qubit systems or specific quantum information processing tasks, being capable of simulating arbitrary quantum processes. The main design factors taken in consideration were ease of use, portability, and performance.
Quantum arithmetic with the Quantum Fourier Transform
Lidia Ruiz-Perez; Juan Carlos Garcia-Escartin
2014-11-21T23:59:59.000Z
The Quantum Fourier Transform offers an interesting way to perform arithmetic operations on a quantum computer. We review existing Quantum Fourier Transform adders and multipliers and propose some modifications that extend their capabilities. Among the new circuits, we propose a quantum method to compute the weighted average of a series of inputs in the transform domain.
Sassoli de Bianchi, Massimiliano, E-mail: autoricerca@gmail.com
2013-09-15T23:59:59.000Z
In a letter to Born, Einstein wrote [42]: “Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the ‘old one.’ I, at any rate, am convinced that He does not throw dice.” In this paper we take seriously Einstein’s famous metaphor, and show that we can gain considerable insight into quantum mechanics by doing something as simple as rolling dice. More precisely, we show how to perform measurements on a single die, to create typical quantum interference effects, and how to connect (entangle) two identical dice, to maximally violate Bell’s inequality. -- Highlights: •Rolling a die is a quantum process admitting a Hilbert space representation. •Rolling experiments with a single die can produce interference effects. •Two connected dice can violate Bell’s inequality. •Correlations need to be created by the measurement, to violate Bell’s inequality.
Surface electromagnetic wave equations in a warm magnetized quantum plasma
Li, Chunhua; Yang, Weihong [Department of Modern Physics, University of Science and Technology of China, 230026 Hefei (China); Wu, Zhengwei, E-mail: wuzw@ustc.edu.cn [Department of Modern Physics, University of Science and Technology of China, 230026 Hefei (China); Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon (Hong Kong); Center of Low Temperature Plasma Application, Yunnan Aerospace Industry Company, Kunming, 650229 Yunnan (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon (Hong Kong)
2014-07-15T23:59:59.000Z
Based on the single-fluid plasma model, a theoretical investigation of surface electromagnetic waves in a warm quantum magnetized inhomogeneous plasma is presented. The surface electromagnetic waves are assumed to propagate on the plane between a vacuum and a warm quantum magnetized plasma. The quantum magnetohydrodynamic model includes quantum diffraction effect (Bohm potential), and quantum statistical pressure is used to derive the new dispersion relation of surface electromagnetic waves. And the general dispersion relation is analyzed in some special cases of interest. It is shown that surface plasma oscillations can be propagated due to quantum effects, and the propagation velocity is enhanced. Furthermore, the external magnetic field has a significant effect on surface wave's dispersion equation. Our work should be of a useful tool for investigating the physical characteristic of surface waves and physical properties of the bounded quantum plasmas.
Quantum Error Correction for Quantum Memories
Barbara M. Terhal
2015-01-20T23:59:59.000Z
Active quantum error correction using qubit stabilizer codes has emerged as a promising, but experimentally challenging, engineering program for building a universal quantum computer. In this review we consider the formalism of qubit stabilizer and subsystem stabilizer codes and their possible use in protecting quantum information in a quantum memory. We review the theory of fault-tolerance and quantum error-correction, discuss examples of various codes and code constructions, the general quantum error correction conditions, the noise threshold, the special role played by Clifford gates and the route towards fault-tolerant universal quantum computation. The second part of the review is focused on providing an overview of quantum error correction using two-dimensional (topological) codes, in particular the surface code architecture. We discuss the complexity of decoding and the notion of passive or self-correcting quantum memories. The review does not focus on a particular technology but discusses topics that will be relevant for various quantum technologies.
Quantum computing in a piece of glass
Warner A. Miller; Grigoriy Kreymerman; Christopher Tison; Paul M. Alsing; Jonathan R. McDonald
2011-12-15T23:59:59.000Z
Quantum gates and simple quantum algorithms can be designed utilizing the diffraction phenomena of a photon within a multiplexed holographic element. The quantum eigenstates we use are the photon's linear momentum (LM) as measured by the number of waves of tilt across the aperture. Two properties of quantum computing within the circuit model make this approach attractive. First, any conditional measurement can be commuted in time with any unitary quantum gate - the timeless nature of quantum computing. Second, photon entanglement can be encoded as a superposition state of a single photon in a higher-dimensional state space afforded by LM. Our theoretical and numerical results indicate that OptiGrate's photo-thermal refractive (PTR) glass is an enabling technology. We will review our previous design of a quantum projection operator and give credence to this approach on a representative quantum gate grounded on coupled-mode theory and numerical simulations, all with parameters consistent with PTR glass. We discuss the strengths (high efficiencies, robustness to environment) and limitations (scalability, crosstalk) of this technology. While not scalable, the utility and robustness of such optical elements for broader quantum information processing applications can be substantial.
Polynomial simulations of decohered quantum computers
Aharonov, D.; Ben-Or, M. [Hebrew Univ., Jerusalem (Israel)
1996-12-31T23:59:59.000Z
Recently it has become clear, that a key issue in quantum computation is understanding how interaction with the environment, or {open_quote}decoherence{close_quotes}, effects the computational power of quantum computers. We adopt the standard physical method of describing systems which are interwound with their environment by {open_quotes}density matrices{close_quotes}, and within this framework define a model of decoherence in quantum computation. Our results show that the computational power of decohered quantum computers depends strongly on the amount of parallelism in the computation. We first present a simulation of decohered sequential quantum computers, on a classical probabilistic Turing machine, and prove that the expected slowdown of this simulation is polynomial in time and space of the quantum computation, for any non zero decoherence rate. Similar results hold for Quantum computers that are allowed to operate on logarithmic number of qubits at a time. For decohered quantum circuits (with local gates), the situation is more subtle and depends on the decoherence rate, {eta}. We find that our simulation is efficient for circuits with decoherence rate {eta} higher than some constant {eta}{sub 1}, but exponential for a general (random) circuit subjected to decoherence rate lower than some constant {eta}{sub 2}. The transition from exponential cost to polynomial cost happens in a short range of decoherence rates. We use computer experiments to exhibit the phase transitions in various quantum circuits.
Quantum Heat Engines Using Superconducting Quantum Circuits
H. T. Quan; Y. D. Wang; Yu-xi Liu; C. P. Sun; Franco Nori
2006-09-14T23:59:59.000Z
We propose a quantum analog of the internal combustion engine used in most cars. Specifically, we study how to implement the Otto-type quantum heat engine (QHE) with the assistance of a Maxwell's demon. Three steps are required: thermalization, quantum measurement, and quantum feedback controlled by the Maxwell demon. We derive the positive-work condition of this composite QHE. Our QHE can be constructed using superconducting quantum circuits. We explicitly demonstrate the essential role of the demon in this macroscopic QHE.
Modeling of the quantum dot filling and the dark current of quantum dot infrared photodetectors
Ameen, Tarek A.; El-Batawy, Yasser M.; Abouelsaood, A. A. [Department of Engineering Mathematics and Physics, Faculty of Engineering, Cairo University, Giza (Egypt)
2014-02-14T23:59:59.000Z
A generalized drift-diffusion model for the calculation of both the quantum dot filling profile and the dark current of quantum dot infrared photodetectors is proposed. The confined electrons inside the quantum dots produce a space-charge potential barrier between the two contacts, which controls the quantum dot filling and limits the dark current in the device. The results of the model reasonably agree with a published experimental work. It is found that increasing either the doping level or the temperature results in an exponential increase of the dark current. The quantum dot filling turns out to be nonuniform, with a dot near the contacts containing more electrons than one in the middle of the device where the dot occupation approximately equals the number of doping atoms per dot, which means that quantum dots away from contacts will be nearly unoccupied if the active region is undoped.
Solving for the Particle-Number-Projected HFB Wavefunction
L. Y. Jia
2015-01-15T23:59:59.000Z
Recently we proposed a particle-number-conserving theory for nuclear pairing [Jia, Phys. Rev. C 88, 044303 (2013)] through the generalized density matrix formalism. The relevant equations were solved for the case when each single-particle level has a distinct set of quantum numbers and could only pair with its time-reversed partner (BCS-type Hamiltonian). In this work we consider the more general situation when several single-particle levels could have the same set of quantum numbers and pairing among these levels is allowed (HFB-type Hamiltonian). The pair condensate wavefunction (the HFB wavefunction projected onto good particle number) is determined by the equations of motion for density matrix operators instead of the variation principle. The theory is tested in the simple two-level model with factorizable pairing interactions and the semi-realistic model with the zero-range delta interaction.
Treating Time Travel Quantum Mechanically
John-Mark A. Allen
2014-10-10T23:59:59.000Z
The fact that closed timelike curves (CTCs) are permitted by general relativity raises the question as to how quantum systems behave when time travel to the past occurs. Research into answering this question by utilising the quantum circuit formalism has given rise to two theories: Deutschian-CTCs (D-CTCs) and "postselected" CTCs (P-CTCs). In this paper the quantum circuit approach is thoroughly reviewed, and the strengths and shortcomings of D-CTCs and P-CTCs are presented in view of their non-linearity and time travel paradoxes. In particular, the "equivalent circuit model"---which aims to make equivalent predictions to D-CTCs, while avoiding some of the difficulties of the original theory---is shown to contain errors. The discussion of D-CTCs and P-CTCs is used to motivate an analysis of the features one might require of a theory of quantum time travel, following which two overlapping classes of new theories are identified. One such theory, the theory of "transition probability" CTCs (T-CTCs), is fully developed. The theory of T-CTCs is shown not to have certain undesirable features---such as time travel paradoxes, the ability to distinguish non-orthogonal states with certainty, and the ability to clone or delete arbitrary pure states---that are present with D-CTCs and P-CTCs. The problems with non-linear extensions to quantum mechanics are discussed in relation to the interpretation of these theories, and the physical motivations of all three theories are discussed and compared.
Replication regulates volume weighting in quantum cosmology
Hartle, James [Department of Physics, University of California, Santa Barbara, California 93106 (United States); Hertog, Thomas [APC, UMR 7164 (CNRS, Universite Paris 7), 10 rue A.Domon et L.Duquet, 75205 Paris (France) and Intl Solvay Institutes, Boulevard du Triomphe, ULB-C.P. 231, 1050 Brussels (Belgium)
2009-09-15T23:59:59.000Z
Probabilities for observations in cosmology are conditioned both on the Universe's quantum state and on local data specifying the observational situation. We show the quantum state defines a measure for prediction through such conditional probabilities that is well-behaved for spatially large or infinite universes when the probabilities that our data are replicated are taken into account. In histories where our data are rare volume weighting connects top-down probabilities conditioned on both the data and the quantum state to the bottom-up probabilities conditioned on the quantum state alone. We apply these principles to a calculation of the number of inflationary e-folds in a homogeneous, isotropic minisuperspace model with a single scalar field moving in a quadratic potential. We find that volume weighting is justified and the top-down probabilities favor a large number of e-folds, hereby predicting the curvature of our Universe at the present time to be approximately zero.
Quantum Strongly Secure Ramp Secret Sharing
Paul Zhang; Ryutaroh Matsumoto
2014-08-08T23:59:59.000Z
Quantum secret sharing is a scheme for encoding a quantum state (the secret) into multiple shares and distributing them among several participants. If a sufficient number of shares are put together, then the secret can be fully reconstructed. If an insufficient number of shares are put together however, no information about the secret can be revealed. In quantum ramp secret sharing, partial information about the secret is allowed to leak to a set of participants, called an unqualified set, that cannot fully reconstruct the secret. By allowing this, the size of a share can be drastically reduced. This paper introduces a quantum analog of classical strong security in ramp secret sharing schemes. While the ramp secret sharing scheme still leaks partial information about the secret to unqualified sets of participants, the strong security condition ensures that qudits with critical information can no longer be leaked.
Adiabatically implementing quantum gates
Sun, Jie; Lu, Songfeng, E-mail: lusongfeng@hotmail.com; Liu, Fang [School of Computer Science and Technology, Huazhong University of Science and Technology, Wuhan 430074 (China)
2014-06-14T23:59:59.000Z
We show that, through the approach of quantum adiabatic evolution, all of the usual quantum gates can be implemented efficiently, yielding running time of order O(1). This may be considered as a useful alternative to the standard quantum computing approach, which involves quantum gates transforming quantum states during the computing process.
How detrimental is decoherence in adiabatic quantum computation?
Tameem Albash; Daniel A. Lidar
2015-03-30T23:59:59.000Z
Recent experiments with increasingly larger numbers of qubits have sparked renewed interest in adiabatic quantum computation, and in particular quantum annealing. A central question that is repeatedly asked is whether quantum features of the evolution can survive over the long time-scales used for quantum annealing relative to standard measures of the decoherence time. We reconsider the role of decoherence in adiabatic quantum computation and quantum annealing using the adiabatic quantum master equation formalism. We restrict ourselves to the weak-coupling and singular-coupling limits, which correspond to decoherence in the energy eigenbasis and in the computational basis, respectively. We demonstrate that decoherence in the instantaneous energy eigenbasis does not necessarily detrimentally affect adiabatic quantum computation, and in particular that a short single-qubit $T_2$ time need not imply adverse consequences for the success of the quantum adiabatic algorithm. We further demonstrate that boundary cancellation methods, designed to improve the fidelity of adiabatic quantum computing in the closed system setting, remain beneficial in the open system setting. To address the high computational cost of master equation simulations, we also demonstrate that a quantum Monte Carlo algorithm that explicitly accounts for a thermal bosonic bath can be used to interpolate between classical and quantum annealing. Our study highlights and clarifies the significantly different role played by decoherence in the adiabatic and circuit models of quantum computing.
Nelson, R.N. (ed.)
1985-05-01T23:59:59.000Z
This publication lists all report number codes processed by the Office of Scientific and Technical Information. The report codes are substantially based on the American National Standards Institute, Standard Technical Report Number (STRN)-Format and Creation Z39.23-1983. The Standard Technical Report Number (STRN) provides one of the primary methods of identifying a specific technical report. The STRN consists of two parts: The report code and the sequential number. The report code identifies the issuing organization, a specific program, or a type of document. The sequential number, which is assigned in sequence by each report issuing entity, is not included in this publication. Part I of this compilation is alphabetized by report codes followed by issuing installations. Part II lists the issuing organization followed by the assigned report code(s). In both Parts I and II, the names of issuing organizations appear for the most part in the form used at the time the reports were issued. However, for some of the more prolific installations which have had name changes, all entries have been merged under the current name.
Quantum Properties of Cavity Cerenkov Radiation
Gao, J; Gao, Ju; Shen, Fang
2005-01-01T23:59:59.000Z
Cerenkov radiation from cavities have been analyzed by quantum electrodynamic theory. Analytical expressions of some basic radiation properties including Einstein's $A$ and $B$ coefficients are derived and shown to be directly modified by the cavities. Coherent and incoherent radiations are analyzed with the aim of generating THz radiation from the devices.
Energy Content of Quantum Systems and the Alleged Collapse of the Wavefunction
Peter J. Riggs
2009-10-15T23:59:59.000Z
It is shown that within a quantum system, the wave field has a (potential) energy content that can be exchanged with quantum particles. Energy conservation in quantum systems holds if potential energy is correctly taken to be a field attribute. From this perspective, a transfer of energy occurs on measurement from the wave field to a quantum particle and this provides a physical explanation of what is commonly referred to as the collapse of the wavefunction.
Matroids and quantum-secret-sharing schemes
Sarvepalli, Pradeep; Raussendorf, Robert [Department of Physics and Astronomy, University of British Columbia, Vancouver V6T 1Z1 (Canada)
2010-05-15T23:59:59.000Z
A secret-sharing scheme is a cryptographic protocol to distribute a secret state in an encoded form among a group of players such that only authorized subsets of the players can reconstruct the secret. Classically, efficient secret-sharing schemes have been shown to be induced by matroids. Furthermore, access structures of such schemes can be characterized by an excluded minor relation. No such relations are known for quantum secret-sharing schemes. In this paper we take the first steps toward a matroidal characterization of quantum-secret-sharing schemes. In addition to providing a new perspective on quantum-secret-sharing schemes, this characterization has important benefits. While previous work has shown how to construct quantum-secret-sharing schemes for general access structures, these schemes are not claimed to be efficient. In this context the present results prove to be useful; they enable us to construct efficient quantum-secret-sharing schemes for many general access structures. More precisely, we show that an identically self-dual matroid that is representable over a finite field induces a pure-state quantum-secret-sharing scheme with information rate 1.
Quantum phase estimation using a multi-headed cat state
Su-Yong Lee; Chang-Woo Lee; Hyunchul Nha; Dagomir Kaszlikowski
2015-03-12T23:59:59.000Z
It was recently shown that an entangled coherent state, which is a superposition of two different coherent states, can surpass the performance of N00N state in estimating an unknown phase-shift. This may hint at further enhancement in phase estimation by incorporating more component states in the superposition of resource state. We here study a four-headed cat state (4HCS), a superposition of four different coherent states, and propose its application to quantum phase estimation. We first investigate how the 4HCS is more nonclassical than a 2HCS in view of some nonclassical measures including sub-Poissonian statistics, negativity of Wigner distribution, and entanglement potential. We then demonstrate the enhanced performance in phase estimation by employing an entangled state via the 4HCS, which can surpass that of the 2HCS particularly in the regime of small average photon number. Moreover, we show that an entangled state modified from the 4HCS can further enhance the phase estimation even in the regime of large average photon number under a photon-loss channel. Our investigation further extends to incorporate an increasingly large number of component states in the resource superposition state and clearly show its merit in phase estimation.
Quantum phase estimation using a multi-headed cat state
Su-Yong Lee; Chang-Woo Lee; Hyunchul Nha; Dagomir Kaszlikowski
2015-05-16T23:59:59.000Z
It was recently shown that an entangled coherent state, which is a superposition of two different coherent states, can surpass the performance of noon state in estimating an unknown phase-shift. This may hint at further enhancement in phase estimation by incorporating more component states in the superposition of resource state. We here introduce a four-headed cat state (4HCS), a superposition of four different coherent states, and propose its application to quantum phase estimation. We demonstrate the enhanced performance in phase estimation by employing an entangled state via the 4HCS, which can surpass that of the two-headed cat state (2HCS), particularly in the regime of small average photon numbers. Moreover, we show that an entangled state modified from the 4HCS can further enhance the phase estimation, even in the regime of large average photon number under a photon-loss channel. Our investigation further extends to incorporate an increasingly large number of component states in the resource superposition state and clearly show its merit in phase estimation.
Decoherence in a dynamical quantum phase transition
Sarah Mostame; Gernot Schaller; Ralf Schützhold
2010-04-15T23:59:59.000Z
Motivated by the similarity between adiabatic quantum algorithms and quantum phase transitions, we study the impact of decoherence on the sweep through a second-order quantum phase transition for the prototypical example of the Ising chain in a transverse field and compare it to the adiabatic version of Grovers search algorithm, which displays a first order quantum phase transition. For site-independent and site-dependent coupling strengths as well as different operator couplings, the results show that (in contrast to first-order transitions) the impact of decoherence caused by a weak coupling to a rather general environment increases with system size (i.e., number of spins/qubits). This might limit the scalability of the corresponding adiabatic quantum algorithm.
Construction of spin models displaying quantum criticality from quantum field theory
Ivan Glasser; J. Ignacio Cirac; Germán Sierra; Anne E. B. Nielsen
2014-07-23T23:59:59.000Z
We provide a method for constructing finite temperature states of one-dimensional spin chains displaying quantum criticality. These models are constructed using correlators of products of quantum fields and have an analytical purification. Their properties can be investigated by Monte-Carlo simulations, which enable us to study the low-temperature phase diagram and to show that it displays a region of quantum criticality. The mixed states obtained are shown to be close to the thermal state of a simple nearest neighbour Hamiltonian.
Quantum Nonsymmetric Gravity and The Superfiber Bundle Formalism
Mebarki, N
1999-01-01T23:59:59.000Z
The formalism of the principal superfiber-bundle is applied to quantum Nonsymmetric gravitationl theory. It is shown that the metric and Faddev-Popov fields arise as superfields components of the superconnection. Moreover,the BRST and anti-BRST transformations are shown to be the gauge transformations of parameters the ghost and anti-ghost superfields.
Holography from quantum cosmology
M. Rashki; S. Jalalzadeh
2014-12-12T23:59:59.000Z
The Weyl-Wigner-Groenewold-Moyal formalism of deformation quantization is applied to the closed Friedmann-Lema\\^itre-Robertson-Walker (FLRW) cosmological model. We show that the phase space average for the surface of the apparent horizon is quantized in units of the Planck's surface, and that the total entropy of the universe is also quantized. Taking into account these two concepts, it is shown that 't Hooft conjecture on the cosmological holographic principle (CHP) in radiation and dust dominated quantum universes is satisfied as a manifestation of quantization. This suggests that the entire universe (not only inside the apparent horizon) can be seen as a two-dimensional information structure encoded on the apparent horizon.
Supersymmetric quantum cosmological billiards
Kleinschmidt, Axel; Koehn, Michael; Nicolai, Hermann [Physique Theorique et Mathematique and International Solvay Institutes, Universite Libre de Bruxelles, Boulevard du Triomphe, ULB-CP231, BE-1050 Bruxelles (Belgium); Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Am Muehlenberg 1, DE-14476 Golm (Germany)
2009-09-15T23:59:59.000Z
D=11 supergravity near a spacelike singularity admits a cosmological billiard description based on the hyperbolic Kac-Moody group E{sub 10}. The quantization of this system via the supersymmetry constraint is shown to lead to wave functions involving automorphic (Maass wave) forms under the modular group W{sup +}(E{sub 10}) congruent with PSL{sub 2}(O) with Dirichlet boundary conditions on the billiard domain. A general inequality for the Laplace eigenvalues of these automorphic forms implies that the wave function of the Universe is generically complex and always tends to zero when approaching the initial singularity. We discuss possible implications of this result for the question of singularity resolution in quantum cosmology and comment on the differences with other approaches.
Why everyone should know number theory Minhyong Kim
Kim, Minhyong
is number' is well-known. But my impression is that even practicing mathematicians are often not entirely (actually for good reasons). Going from the large to the small scale, according to quantum mechanics product in a natural way of many other Hilbert spaces. We can completely trace the evolution of (all
Statistical Estimation of Quantum Tomography Protocols Quality
Yu. I. Bogdanov; G. Brida; M. Genovese; S. P. Kulik; E. V. Moreva; A. P. Shurupov
2010-02-18T23:59:59.000Z
A novel operational method for estimating the efficiency of quantum state tomography protocols is suggested. It is based on a-priori estimation of the quality of an arbitrary protocol by means of universal asymptotic fidelity distribution and condition number, which takes minimal value for better protocol. We prove the adequacy of the method both with numerical modeling and through the experimental realization of several practically important protocols of quantum state tomography.
Maini, Philip K.
Spots and stripes: Pleomorphic patterning of stem cells via p-ERK-dependent cell chemotaxis shown cells Placode ERK Mathematical modeling Chemotaxis A key issue in stem cell biology patterns, ranging from stripes to spots, can be obtained when the level of p-ERK activity is adjusted
Kambhampati, Patanjali
#12;THE `TEST STATISTICS REPORT' provides a synopsis of the test attributes and some important statistics. A sample is shown here to the right. The Test reliability indicators are measures of how well: Are formulae for testing reliability as a measure of internal consistency. Higher values indicate a stronger
Quantum Information Science | ornl.gov
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
Analysis Behavioral Sciences Geographic Information Science and Technology Quantum Information Science Quantum Communication and Security Quantum-Enhanced Sensing Quantum...
Stapp, H.P.
1988-04-01T23:59:59.000Z
It is argued that the validity of the predictions of quantum theory in certain spin-correlation experiments entails a violation of Einstein's locality idea that no causal influence can act outside the forward light cone. First, two preliminary arguments suggesting such a violation are reviewed. They both depend, in intermediate stages, on the idea that the results of certain unperformed experiments are physically determinate. The second argument is entangled also with the problem of the meaning of physical reality. A new argument having neither of these characteristics is constructed. It is based strictly on the orthodox ideas of Bohr and Heisenberg, and has no realistic elements, or other ingredients, that are alien to orthodox quantum thinking.
Computational costs of data definition at the quantum - classical interface
Chris Fields
2010-05-26T23:59:59.000Z
Model-independent semantic requirements for user specification and interpretation of data before and after quantum computations are characterized. Classical computational costs of assigning classical data values to quantum registers and to run-time parameters passed across a classical-to-quantum application programming interface are derived. It is shown that the classical computational costs of data definition equal or exceed the classical computational cost of solving the problem of interest for all applications of quantum computing except computations defined over the integers and the simulation of linear systems with linear boundary conditions.
Relation of classical non-equilibrium dynamics and quantum annealing
Hidetosni Nishimori
2015-03-07T23:59:59.000Z
Non-equilibrium dynamics of the Ising model is a classical stochastic process whereas quantum mechanics has no stochastic elements in the classical sense. Nevertheless, it has been known that there exists a close formal relationship between these two processes. We reformulate this relationship and use it to compare the efficiency of simulated annealing that uses classical stochastic processes and quantum annealing to solve combinatorial optimization problems. It is shown that classical dynamics can be efficiently simulated by quantum-mechanical processes whereas the converse is not necessarily true. This may imply that quantum annealing may be regarded as a more powerful tool than simulated annealing for optimization problems.
Orthogonal-state-based protocols of quantum key agreement
Chitra Shukla; Nasir Alam; Anirban Pathak
2013-10-05T23:59:59.000Z
Two orthogonal-state-based protocols of quantum key agreement (QKA) are proposed. The first protocol of QKA proposed here is designed for two-party QKA, whereas the second protocol is designed for multi-party QKA. Security of these orthogonal-state-based protocols arise from monogamy of entanglement. This is in contrast to the existing protocols of QKA where security arises from the use of non-orthogonal state (non-commutativity principle). Further, it is shown that all the quantum systems that are useful for implementation of quantum dialogue and most of the protocols of secure direct quantum communication can be modified to implement protocols of QKA.
Engineered Quantum Dot Single Photon Sources
Sonia Buckley; Kelley Rivoire; Jelena Vuckovic
2012-10-03T23:59:59.000Z
Fast, high efficiency, and low error single photon sources are required for implementation of a number of quantum information processing applications. The fastest triggered single photon sources to date have been demonstrated using epitaxially grown semiconductor quantum dots (QDs), which can be conveniently integrated with optical microcavities. Recent advances in QD technology, including demonstrations of high temperature and telecommunications wavelength single photon emission, have made QD single photon sources more practical. Here we discuss the applications of single photon sources and their various requirements, before reviewing the progress made on a quantum dot platform in meeting these requirements.
Towards bulk based preconditioning for quantum dotcomputations
Dongarra, Jack; Langou, Julien; Tomov, Stanimire; Channing,Andrew; Marques, Osni; Vomel, Christof; Wang, Lin-Wang
2006-05-25T23:59:59.000Z
This article describes how to accelerate the convergence of Preconditioned Conjugate Gradient (PCG) type eigensolvers for the computation of several states around the band gap of colloidal quantum dots. Our new approach uses the Hamiltonian from the bulk materials constituent for the quantum dot to design an efficient preconditioner for the folded spectrum PCG method. The technique described shows promising results when applied to CdSe quantum dot model problems. We show a decrease in the number of iteration steps by at least a factor of 4 compared to the previously used diagonal preconditioner.
Khan, T.A.; Baum, J.W.; Beckman, M.C. [eds.] [eds.
1993-10-01T23:59:59.000Z
This document contains information dealing with the lessons learned from the experience of nuclear plants. In this issue the authors tried to avoid the `tyranny` of numbers and concentrated on the main lessons learned. Topics include: filtration devices for air pollution abatement, crack repair and inspection, and remote handling equipment.
Quantum radiation at finite temperature
Ralf Schützhold; Günter Plunien; Gerhard Soff
2001-05-23T23:59:59.000Z
We investigate the phenomenon of quantum radiation - i.e. the conversion of (virtual) quantum fluctuations into (real) particles induced by dynamical external conditions - for an initial thermal equilibrium state. For a resonantly vibrating cavity a rather strong enhancement of the number of generated particles (the dynamical Casimir effect) at finite temperatures is observed. Furthermore we derive the temperature corrections to the energy radiated by a single moving mirror and an oscillating bubble within a dielectric medium as well as the number of created particles within the Friedmann-Robertson-Walker universe. Possible implications and the relevance for experimental tests are addressed. PACS: 42.50.Lc, 03.70.+k, 11.10.Ef, 11.10.Wx.
The Planck quantum hypothesis and the Friedmannian models of flat universe
V. Skalsky
2000-09-25T23:59:59.000Z
Only one model from an infinite number of the Friedmannian models of flat expansive isotropic and homogeneous universe satisfies the assumptions resulting from the Planck quantum hypothesis.
Quantum Coherence and Closed Timelike Curves
S. W. Hawking
1995-02-08T23:59:59.000Z
Various calculations of the $S$ matrix have shown that it seems to be non unitary for interacting fields when there are closed timelike curves. It is argued that this is because there is loss of quantum coherence caused by the fact that part of the quantum state circulates on the closed timelike curves and is not measured at infinity. A prescription is given for calculating the superscattering matrix $\\$ $ on space times whose parameters can be analytically continued to obtain a Euclidean metric. It is illustrated by a discussion of a spacetime in with two disks in flat space are identified. If the disks have an imaginary time separation, this corresponds to a heat bath. An external field interacting with the heat bath will lose quantum coherence. One can then analytically continue to an almost real separation of the disks. This will give closed timelike curves but one will still get loss of quantum coherence.
Time-delayed quantum feedback control
Arne L. Grimsmo
2015-02-24T23:59:59.000Z
A theory of time-delayed coherent quantum feedback is developed. More specifically, we consider a quantum system coupled to a bosonic reservoir creating a unidirectional feedback loop. It is shown that the dynamics can be mapped onto a fictitious quantum cascade, where the system is driven by past versions of itself. The derivation of this model relies on a tensor network representation of the system-reservoir time-propagator. For concreteness, this general theory is applied to a driven two-level atom scattering into a coherent feedback loop. We demonstrate how delay effects can qualitatively change the dynamics of the atom, and how quantum control can be implemented in the presence of time-delays. A realization with a superconducting qubit serving as an artificial atom is discussed.
Roumen Tsekov
2011-04-15T23:59:59.000Z
A new approach to thermo-quantum diffusion is proposed and a nonlinear quantum Smoluchowski equation is derived, which describes classical diffusion in the field of the Bohm quantum potential. A nonlinear thermo-quantum expression for the diffusion front is obtained, being a quantum generalization of the classical Einstein law. The quantum diffusion at zero temperature is also described and a new dependence of the position dispersion on time is derived. A stochastic Bohm-Langevin equation is also proposed.
Quantum Field Theory & Gravity
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Quantum Field Theory & Gravity Quantum Field Theory & Gravity Understanding discoveries at the Energy, Intensity, and Cosmic Frontiers Get Expertise Rajan Gupta (505) 667-7664...
Reformulating and Reconstructing Quantum Theory
Lucien Hardy
2011-08-25T23:59:59.000Z
We provide a reformulation of finite dimensional quantum theory in the circuit framework in terms of mathematical axioms, and a reconstruction of quantum theory from operational postulates. The mathematical axioms for quantum theory are the following: [Axiom 1] Operations correspond to operators. [Axiom 2] Every complete set of physical operators corresponds to a complete set of operations. The following operational postulates are shown to be equivalent to these mathematical axioms: [P1] Sharpness. Associated with any given pure state is a unique maximal effect giving probability equal to one. This maximal effect does not give probability equal to one for any other pure state. [P2] Information locality. A maximal measurement on a composite system is effected if we perform maximal measurements on each of the components. [P3] Tomographic locality. The state of a composite system can be determined from the statistics collected by making measurements on the components. [P4] Compound permutability. There exists a compound reversible transformation on any system effecting any given permutation of any given maximal set of distinguishable states for that system. [P5] Sturdiness. Filters are non-flattening. Hence, from these postulates we can reconstruct all the usual features of quantum theory: States are represented by positive operators, transformations by completely positive trace non-increasing maps, and effects by positive operators. The Born rule (i.e. the trace rule) for calculating probabilitieso follows. A more detailed abstract is provided in the paper.
A Survey of Quantum Property Testing
Ashley Montanaro; Ronald de Wolf
2014-12-10T23:59:59.000Z
The area of property testing tries to design algorithms that can efficiently handle very large amounts of data: given a large object that either has a certain property or is somehow "far" from having that property, a tester should efficiently distinguish between these two cases. In this survey we describe recent results obtained for quantum property testing. This area naturally falls into three parts. First, we may consider quantum testers for properties of classical objects. We survey the main examples known where quantum testers can be much (sometimes exponentially) more efficient than classical testers. Second, we may consider classical testers of quantum objects. This is the situation that arises for instance when one is trying to determine if quantum states or operations do what they are supposed to do, based only on classical input-output behavior. Finally, we may also consider quantum testers for properties of quantum objects, such as states or operations. We survey known bounds on testing various natural properties, such as whether two states are equal, whether a state is separable, whether two operations commute, etc. We also highlight connections to other areas of quantum information theory and mention a number of open questions.
Efficient multiparty quantum-secret-sharing schemes
Xiao Li; Deng Fuguo [Department of Physics, Tsinghua University, Beijing 100084 (China); Key Laboratory for Quantum Information and Measurements, MOE, Beijing 100084 (China); Long Guilu [Department of Physics, Tsinghua University, Beijing 100084 (China); Key Laboratory for Quantum Information and Measurements, MOE, Beijing 100084 (China); Center of Atomic and Molecular NanoSciences, Tsinghua University, Beijing 100084 (China); Center for Quantum Information, Tsinghua University, Beijing 100084 (China); Pan Jianwei [Institute for Experimental Physics University of Vienna, Boltzmanngasse 5, Vienna 9 (Austria)
2004-05-01T23:59:59.000Z
In this work, we generalize the quantum-secret-sharing scheme of Hillery, Buzek, and Berthiaume [Phys. Rev. A 59, 1829 (1999)] into arbitrary multiparties. Explicit expressions for the shared secret bit is given. It is shown that in the Hillery-Buzek-Berthiaume quantum-secret-sharing scheme the secret information is shared in the parity of binary strings formed by the measured outcomes of the participants. In addition, we have increased the efficiency of the quantum-secret-sharing scheme by generalizing two techniques from quantum key distribution. The favored-measuring-basis quantum-secret-sharing scheme is developed from the Lo-Chau-Ardehali technique [H. K. Lo, H. F. Chau, and M. Ardehali, e-print quant-ph/0011056] where all the participants choose their measuring-basis asymmetrically, and the measuring-basis-encrypted quantum-secret-sharing scheme is developed from the Hwang-Koh-Han technique [W. Y. Hwang, I. G. Koh, and Y. D. Han, Phys. Lett. A 244, 489 (1998)] where all participants choose their measuring basis according to a control key. Both schemes are asymptotically 100% in efficiency, hence nearly all the Greenberger-Horne-Zeilinger states in a quantum-secret-sharing process are used to generate shared secret information.
Extractable work from ensembles of quantum batteries. Entanglement helps
Robert Alicki; Mark Fannes
2012-11-19T23:59:59.000Z
Motivated by the recent interest in thermodynamics of micro- and mesoscopic quantum systems we study the maximal amount of work that can be reversibly extracted from a quantum system used to store temporarily energy. Guided by the notion of passivity of a quantum state we show that entangling unitary controls extract in general more work than independent ones. In the limit of large number of copies one can reach the thermodynamical bound given by the variational principle for free energy.
Fake state attack on practically decoy state quantum key distribution
Yong-gang Tan
2012-02-15T23:59:59.000Z
In this paper, security of practically decoy state quantum key distribution under fake state attack is considered. If quantum key distribution is insecure under this type of attack, decoy sources can not also provide it with enough security. Strictly analysis shows that Eve should eavesdrop with the aid of photon-number-resolving instruments. In practical implementation of decoy state quantum key distribution where statistical fluctuation is considered, however, Eve can attack it successfully with threshold detectors.
Entropy and Area of Black Holes in Loop Quantum Gravity
I. B. Khriplovich
2002-03-31T23:59:59.000Z
Simple arguments related to the entropy of black holes strongly constrain the spectrum of the area operator for a Schwarzschild black hole in loop quantum gravity. In particular, this spectrum is fixed completely by the assumption that the black hole entropy is maximum. Within the approach discussed, one arrives in loop quantum gravity at a quantization rule with integer quantum numbers $n$ for the entropy and area of a black hole.
Imperfection effects for multiple applications of the quantum wavelet transform
Marcello Terraneo; Dima L. Shepelyansky
2003-03-09T23:59:59.000Z
We study analytically and numerically the effects of various imperfections in a quantum computation of a simple dynamical model based on the Quantum Wavelet Transform (QWT). The results for fidelity timescales, obtained for a large range of error amplitudes and number of qubits, imply that for static imperfections the threshold for fault-tolerant quantum computation is decreased by a few orders of magnitude compared to the case of random errors.
Quantum Leap Quantum Mechanics' Killer App
Bigelow, Stephen
Quantum Leap Quantum Mechanics' Killer App Q&A with Craig Hawker Director of the Materials Research. Q&A with Craig Hawker LEAP The Materials Research Laboratory is the only Wes
Optimisation of Quantum Evolution Algorithms
Apoorva Patel
2015-03-04T23:59:59.000Z
Given a quantum Hamiltonian and its evolution time, the corresponding unitary evolution operator can be constructed in many different ways, corresponding to different trajectories between the desired end-points. A choice among these trajectories can then be made to obtain the best computational complexity and control over errors. As an explicit example, Grover's quantum search algorithm is described as a Hamiltonian evolution problem. It is shown that the computational complexity has a power-law dependence on error when a straightforward Lie-Trotter discretisation formula is used, and it becomes logarithmic in error when reflection operators are used. The exponential change in error control is striking, and can be used to improve many importance sampling methods. The key concept is to make the evolution steps as large as possible while obeying the constraints of the problem. In particular, we can understand why overrelaxation algorithms are superior to small step size algorithms.
Optimisation of Quantum Evolution Algorithms
Patel, Apoorva
2015-01-01T23:59:59.000Z
Given a quantum Hamiltonian and its evolution time, the corresponding unitary evolution operator can be constructed in many different ways, corresponding to different trajectories between the desired end-points. A choice among these trajectories can then be made to obtain the best computational complexity and control over errors. As an explicit example, Grover's quantum search algorithm is described as a Hamiltonian evolution problem. It is shown that the computational complexity has a power-law dependence on error when a straightforward Lie-Trotter discretisation formula is used, and it becomes logarithmic in error when reflection operators are used. The exponential change in error control is striking, and can be used to improve many importance sampling methods. The key concept is to make the evolution steps as large as possible while obeying the constraints of the problem. In particular, we can understand why overrelaxation algorithms are superior to small step size algorithms.
Gauge Theory of Quantum Gravity
J. W. Moffat
1994-01-04T23:59:59.000Z
A gauge theory of quantum gravity is formulated, in which an internal, field dependent metric is introduced which non-linearly realizes the gauge fields on the non-compact group $SL(2,C)$, while linearly realizing them on $SU(2)$. Einstein's $SL(2,C)$ invariant theory of gravity emerges at low energies, since the extra degrees of freedom associated with the quadratic curvature and the internal metric only dominate at high energies. In a fixed internal metric gauge, only the the $SU(2)$ gauge symmetry is satisfied, the particle spectrum is identified and the Hamiltonian is shown to be bounded from below. Although Lorentz invariance is broken in this gauge, it is satisfied in general. The theory is quantized in this fixed, broken symmetry gauge as an $SU(2)$ gauge theory on a lattice with a lattice spacing equal to the Planck length. This produces a unitary and finite theory of quantum gravity.
Quantum walks and relativistic quantum simulations
Blatt, Rainer
in a quantum simulation of the Klein para- dox. The position and momentum of a relativistic Dirac particle
Quantum coherence and correlations in quantum system
Zhengjun Xi; Yongming Li; Heng Fan
2014-12-24T23:59:59.000Z
Criteria of measure quantifying quantum coherence, a unique property of quantum system, are proposed recently. In this paper, we firstly give an uncertainty-like expression relating the coherence and the entropy of quantum system. Then, we obtain three trade-offs among the coherence, the discord and the deficit in the bipartite quantum system.As a consequence, we obtain that the relative entropy of coherence satisfies the super-additivity. Finally, we discuss the relations between the entanglement and the coherence.
Stránský, Pavel [Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovi?kách 2, 18000 Prague (Czech Republic); Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 04510, México, D.F. (Mexico); Macek, Michal [Racah Institute of Physics, The Hebrew University, 91904 Jerusalem (Israel); Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovi?kách 2, 18000 Prague (Czech Republic); Cejnar, Pavel, E-mail: pavel.cejnar@mff.cuni.cz [Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovi?kách 2, 18000 Prague (Czech Republic)
2014-06-15T23:59:59.000Z
Quantum systems with a finite number of freedom degrees f develop robust singularities in the energy spectrum of excited states as the system’s size increases to infinity. We analyze the general form of these singularities for low f, particularly f=2, clarifying the relation to classical stationary points of the corresponding potential. Signatures in the smoothed energy dependence of the quantum state density and in the flow of energy levels with an arbitrary control parameter are described along with the relevant thermodynamical consequences. The general analysis is illustrated with specific examples of excited-state singularities accompanying the first-order quantum phase transition. -- Highlights: •ESQPTs found in infinite-size limit of systems with low numbers of freedom degrees f. •ESQPTs related to non-analytical evolutions of classical phase–space properties. •ESQPT signatures analyzed for general f, particularly f=2, extending known case f=1. •ESQPT signatures identified in smoothened density and flow of energy spectrum. •ESQPTs shown to induce a new type of thermodynamic anomalies.
Trovato, M. [Dipartimento di Matematica, Universita di Catania, Viale A. Doria, I-95125 Catania (Italy); Reggiani, L. [Dipartimento di Ingegneria dell' Innovazione and CNISM, Universita del Salento, Via Arnesano s/n, I-73100 Lecce (Italy)
2011-12-15T23:59:59.000Z
By introducing a quantum entropy functional of the reduced density matrix, the principle of quantum maximum entropy is asserted as fundamental principle of quantum statistical mechanics. Accordingly, we develop a comprehensive theoretical formalism to construct rigorously a closed quantum hydrodynamic transport within a Wigner function approach. The theoretical formalism is formulated in both thermodynamic equilibrium and nonequilibrium conditions, and the quantum contributions are obtained by only assuming that the Lagrange multipliers can be expanded in powers of ({h_bar}/2{pi}){sup 2}. In particular, by using an arbitrary number of moments, we prove that (1) on a macroscopic scale all nonlocal effects, compatible with the uncertainty principle, are imputable to high-order spatial derivatives, both of the numerical density n and of the effective temperature T; (2) the results available from the literature in the framework of both a quantum Boltzmann gas and a degenerate quantum Fermi gas are recovered as a particular case; (3) the statistics for the quantum Fermi and Bose gases at different levels of degeneracy are explicitly incorporated; (4) a set of relevant applications admitting exact analytical equations are explicitly given and discussed; (5) the quantum maximum entropy principle keeps full validity in the classical limit, when ({h_bar}/2{pi}){yields}0.
Asymptotically Optimal Quantum Circuits for d-Level Systems Stephen S. Bullock,1
O'Leary, Dianne P.
Asymptotically Optimal Quantum Circuits for d-Level Systems Stephen S. Bullock,1 Dianne P. O by the number of entangling gates, depends on the subsystem size. We examine the quantum circuit complexity circuit [1] acting on qubits. Multilevel quantum logics have been proposed as an alternative to qubits due
Ooi, C. H. Raymond [Department of Physics, University of Malaya, 50603 Kuala Lumpur (Malaysia)
2011-04-15T23:59:59.000Z
It is shown that thermal energy from a heat source can be converted to useful work in the form of maser-laser light by using a combination of a Stern-Gerlach device and stimulated emissions of excited particles in a maser-laser cavity. We analyze the populations of atoms or quantum dots exiting the cavity, the photon statistics, and the internal entropy as a function of atomic transit time, using the quantum theory of masers and lasers. The power of the laser light is estimated to be sufficiently high for device applications. The thermodynamics of the heat converter is analyzed as a heat engine operating between two reservoirs of different temperature but is generalized to include the change of internal quantum states. The von Neumann entropies for the internal degree are obtained. The sum of the internal and external entropies increases after each cycle and the second law is not violated, even if the photon entropy due to finite photon number distribution is not included. An expression for efficiency relating to the Carnot efficiency is obtained. We resolve the subtle paradox on the reduction of the internal entropy with regards to the path separation after the Stern-Gerlach device.
Photon number squeezing of ultra-broadband laser pulses generated by microstructure fibers
K. Hirosawa; H. Furumochi; A. Tada; F. Kannari; M. Takeoka; M. Sasaki
2005-01-10T23:59:59.000Z
To the best of our knowledge, we demonstrate for the first time the generation of photon number squeezing by spectral filtering for ultra-broadband light generated by microstructure fibers at 800 nm. A maximum squeezing of 4.6 dB is observed, corresponding to 10.3 dB after correcting for detection losses. We numerically analyzed the quantum dynamics of ultrashort laser pulse propagation through optical fibers by solving a nonlinear quantum Schrodinger equation that included Raman scattering, especially for the quantum correlation of photon number fluctuation among frequency modes in broadband pulses.
Topological color codes and two-body quantum lattice Hamiltonians
Kargarian, M.
Topological color codes are among the stabilizer codes with remarkable properties from the quantum information perspective. In this paper, we construct a lattice, the so-called ruby lattice, with coordination number 4 ...
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Ground State Quantum Computation
Ari Mizel; M. W. Mitchell; Marvin L. Cohen
1999-08-11T23:59:59.000Z
We formulate a novel ground state quantum computation approach that requires no unitary evolution of qubits in time: the qubits are fixed in stationary states of the Hamiltonian. This formulation supplies a completely time-independent approach to realizing quantum computers. We give a concrete suggestion for a ground state quantum computer involving linked quantum dots.
Localized quantum walks as secured quantum memory
C. M. Chandrashekar; Th. Busch
2015-04-21T23:59:59.000Z
We show that a quantum walk process can be used to construct and secure quantum memory. More precisely, we show that a localized quantum walk with temporal disorder can be engineered to store the information of a single, unknown qubit on a compact position space and faithfully recover it on demand. Since the localization occurss with a finite spread in position space, the stored information of the qubit will be naturally secured from the simple eavesdropper. Our protocol can be adopted to any quantum system for which experimental control over quantum walk dynamics can be achieved.
The quantum cryptographic switch
Srinatha Narayanaswamy; Omkar Srikrishna; R. Srikanth; Subhashish Banerjee; Anirban Pathak
2011-11-21T23:59:59.000Z
We illustrate using a quantum system the principle of a cryptographic switch, in which a third party (Charlie) can control to a continuously varying degree the amount of information the receiver (Bob) receives, after the sender (Alice) has sent her information. Suppose Charlie transmits a Bell state to Alice and Bob. Alice uses dense coding to transmit two bits to Bob. Only if the 2-bit information corresponding to choice of Bell state is made available by Charlie to Bob can the latter recover Alice's information. By varying the information he gives, Charlie can continuously vary the information recovered by Bob. The performance of the protocol subjected to the squeezed generalized amplitude damping channel is considered. We also present a number of practical situations where a cryptographic switch would be of use.
Quantum search without entanglement
Lloyd, S
2000-01-01T23:59:59.000Z
Entanglement of quantum variables is usually thought to be a prerequisite for obtaining quantum speed-ups of information processing tasks such as searching databases. This paper presents methods for quantum search that give a speed-up over classical methods, but that do not require entanglement. These methods rely instead on interference to provide a speed-up. Search without entanglement comes at a cost: although they outperform analogous classical devices, the quantum devices that perform the search are not universal quantum computers and require exponentially greater overhead than a quantum computer that operates using entanglement. Quantum search without entanglement is compared to classical search using waves.
Quantum search without entanglement
Seth Lloyd
1999-03-16T23:59:59.000Z
Entanglement of quantum variables is usually thought to be a prerequisite for obtaining quantum speed-ups of information processing tasks such as searching databases. This paper presents methods for quantum search that give a speed-up over classical methods, but that do not require entanglement. These methods rely instead on interference to provide a speed-up. Search without entanglement comes at a cost: although they outperform analogous classical devices, the quantum devices that perform the search are not universal quantum computers and require exponentially greater overhead than a quantum computer that operates using entanglement. Quantum search without entanglement is compared to classical search using waves.
Quantum Kolmogorov Complexity and the Quantum Turing Machine
Markus Mueller
2007-12-28T23:59:59.000Z
The purpose of this thesis is to give a formal definition of quantum Kolmogorov complexity (QC), and rigorous mathematical proofs of its basic properties. The definition used here is similar to that by Berthiaume, van Dam, and Laplante. It defines the QC of some indeterminate-length qubit string \\rho as the minimum base length of any quantum input which makes a quantum Turing machine (QTM) halt and output \\rho, up to some error tolerance. First, we prove that there is a QTM which is universal in the sense of input base length. Furthermore, we show several general properties of QTMs, including a result on mutually orthogonal ``halting spaces'', and a way to transform every almost-halting input into a deterministically-halting input by adding at most a constant number of qubits. Afterwards, we apply these results to QC. In particular, we show that QC is invariant, incompressible, agrees with classical Kolmogorov complexity for classical strings, and is closely related to von Neumann entropy for ergodic quantum information sources.
Ideal Quantum Gases with Planck Scale Limitations
Rainer Collier
2015-03-14T23:59:59.000Z
A thermodynamic system of non-interacting quantum particles changes its statistical distribution formulas if there is a universal limitation for the size of energetic quantum leaps (magnitude of quantum leaps smaller than Planck energy). By means of a restriction of the a priori equiprobability postulate one can reach a thermodynamic foundation of these corrected distribution formulas. The number of microstates is determined by means of a suitable counting method and combined with thermodynamics via the Boltzmann principle. The result is that, for particle energies that come close to the Planck energy, the thermodynamic difference between fermion and boson distribution vanishes. Both distributions then approximate a Boltzmann distribution. The wave and particle character of the quantum particles, too, can be influenced by choosing the size of the temperature and particle energy parameters relative to the Planck energy, as you can see from the associated fluctuation formulas. In the case of non-relativistic degeneration, the critical parameters Fermi momentum (fermions) and Einstein temperature (bosons) vanish as soon as the rest energy of the quantum particles reaches the Planck energy. For the Bose-Einstein condensation there exists, in the condensation range, a finite upper limit for the number of particles in the ground state, which is determined by the ratio of Planck mass to the rest mass of the quantum particles. In the relativistic high-temperature range, the energy densities of photon and neutrino radiation have finite limit values, which is of interest with regard to the start of cosmic expansion.
Grant Application Package CFDA Number
Talley, Lynne D.
Grant Application Package CFDA Number: Opportunity Title: Offering Agency: Agency Contact: Opportunity Open Date: Opportunity Close Date: CFDA Description: Opportunity Number: Competition ID
Counting degrees of freedom in quantum field theory using entanglement entropy
Mezei, Márk (Márk Koppany)
2014-01-01T23:59:59.000Z
We devote this thesis to the exploration of how to define the number of degrees of freedom in quantum field theory. Intuitively, the number of degrees of freedom should decrease along the renormalization group (RG) flow, ...
Quantum Thermodynamic Cycles and quantum heat engines
H. T. Quan; Yu-xi Liu; C. P. Sun; Franco Nori
2007-04-03T23:59:59.000Z
In order to describe quantum heat engines, here we systematically study isothermal and isochoric processes for quantum thermodynamic cycles. Based on these results the quantum versions of both the Carnot heat engine and the Otto heat engine are defined without ambiguities. We also study the properties of quantum Carnot and Otto heat engines in comparison with their classical counterparts. Relations and mappings between these two quantum heat engines are also investigated by considering their respective quantum thermodynamic processes. In addition, we discuss the role of Maxwell's demon in quantum thermodynamic cycles. We find that there is no violation of the second law, even in the existence of such a demon, when the demon is included correctly as part of the working substance of the heat engine.
A Graphic Representation of States for Quantum Copying Machines
Sara Felloni; Giuliano Strini
2006-09-29T23:59:59.000Z
The aim of this paper is to introduce a new graphic representation of quantum states by means of a specific application: the analysis of two models of quantum copying machines. The graphic representation by diagrams of states offers a clear and detailed visualization of quantum information's flow during the unitary evolution of not too complex systems. The diagrams of states are exponentially more complex in respect to the standard representation and this clearly illustrates the discrepancy of computational power between quantum and classical systems. After a brief introductive exposure of the general theory, we present a constructive procedure to illustrate the new representation by means of concrete examples. Elementary diagrams of states for single-qubit and two-qubit systems and a simple scheme to represent entangled states are presented. Quantum copying machines as imperfect cloners of quantum states are introduced and the quantum copying machines of Griffiths and Niu and of Buzek and Hillery are analyzed, determining quantum circuits of easier interpretation. The method has indeed shown itself to be extremely successful for the representation of the involved quantum operations and it has allowed to point out the characteristic aspects of the quantum computations examined.
Bilinear covariants and spinor fields duality in quantum Clifford algebras
Ab?amowicz, Rafa?, E-mail: rablamowicz@tntech.edu [Department of Mathematics, Box 5054, Tennessee Technological University, Cookeville, Tennessee 38505 (United States); Gonçalves, Icaro, E-mail: icaro.goncalves@ufabc.edu.br [Instituto de Matemática e Estatística, Universidade de São Paulo, Rua do Matão, 1010, 05508-090, São Paulo, SP (Brazil); Centro de Matemática, Computação e Cognição, Universidade Federal do ABC, 09210-170 Santo André, SP (Brazil); Rocha, Roldão da, E-mail: roldao.rocha@ufabc.edu.br [Centro de Matemática, Computação e Cognição, Universidade Federal do ABC, 09210-170 Santo André, SP (Brazil); International School for Advanced Studies (SISSA), Via Bonomea 265, 34136 Trieste (Italy)
2014-10-15T23:59:59.000Z
Classification of quantum spinor fields according to quantum bilinear covariants is introduced in a context of quantum Clifford algebras on Minkowski spacetime. Once the bilinear covariants are expressed in terms of algebraic spinor fields, the duality between spinor and quantum spinor fields can be discussed. Thus, by endowing the underlying spacetime with an arbitrary bilinear form with an antisymmetric part in addition to a symmetric spacetime metric, quantum algebraic spinor fields and deformed bilinear covariants can be constructed. They are thus compared to the classical (non quantum) ones. Classes of quantum spinor fields classes are introduced and compared with Lounesto's spinor field classification. A physical interpretation of the deformed parts and the underlying Z-grading is proposed. The existence of an arbitrary bilinear form endowing the spacetime already has been explored in the literature in the context of quantum gravity [S. W. Hawking, “The unpredictability of quantum gravity,” Commun. Math. Phys. 87, 395 (1982)]. Here, it is shown further to play a prominent role in the structure of Dirac, Weyl, and Majorana spinor fields, besides the most general flagpoles and flag-dipoles. We introduce a new duality between the standard and the quantum spinor fields, by showing that when Clifford algebras over vector spaces endowed with an arbitrary bilinear form are taken into account, a mixture among the classes does occur. Consequently, novel features regarding the spinor fields can be derived.
On Quantum and Classical BCH Codes
Salah A. Aly; Andreas Klappenecker; Pradeep Kiran Sarvepalli
2006-04-14T23:59:59.000Z
Classical BCH codes that contain their (Euclidean or Hermitian) dual codes can be used to construct quantum stabilizer codes; this correspondence studies the properties of such codes. It is shown that a BCH code of length n can contain its dual code only if its designed distance d=O(sqrt(n)), and the converse is proved in the case of narrow-sense codes. Furthermore, the dimension of narrow-sense BCH codes with small design distance is completely determined, and - consequently - the bounds on their minimum distance are improved. These results make it possible to determine the parameters of quantum BCH codes in terms of their design parameters.
Quantum Mechanical Coherence, Resonance, and Mind
Henry P. Stapp
1995-04-04T23:59:59.000Z
Norbert Wiener and J.B.S. Haldane suggested during the early thirties that the profound changes in our conception of matter entailed by quantum theory opens the way for our thoughts, and other experiential or mind-like qualities, to play a role in nature that is causally interactive and effective, rather than purely epiphenomenal, as required by classical mechanics. The mathematical basis of this suggestion is described here, and it is then shown how, by giving mind this efficacious role in natural process, the classical character of our perceptions of the quantum universe can be seen to be a consequence of evolutionary pressures for the survival of the species.
Stochastic Quantum Trajectories without a Wave Function
Jeroen C. Vink
2015-03-16T23:59:59.000Z
After summarizing three versions of trajectory-based quantum mechanics, it is argued that only the original formulation due to Bohm, which uses the Schr\\"odinger wave function to guide the particles, can be readily extended to particles with spin. To extend the two wave function-free formulations, it is argued that necessarily particle trajectories not only determine location, but also spin. Since spin values are discrete, it is natural to revert to a variation of Bohm's pilot wave formulation due originally to Bell. It is shown that within this formulation with stochastic quantum trajectories, a wave function free formulation can be obtained.
Wave Packets Propagation in Quantum Gravity
Kourosh Nozari; S. H. Mehdipour
2005-07-03T23:59:59.000Z
Wave packet broadening in usual quantum mechanics is a consequence of dispersion behavior of the medium which the wave propagates in it. In this paper, we consider the problem of wave packet broadening in the framework of Generalized Uncertainty Principle(GUP) of quantum gravity. New dispersion relations are derived in the context of GUP and it has been shown that there exists a gravitational induced dispersion which leads to more broadening of the wave packets. As a result of these dispersion relations, a generalized Klein-Gordon equation is obtained and its interpretation is given.
Quantum Capacities of Channels with small Environment
Michael M. Wolf; David Perez-Garcia
2006-07-11T23:59:59.000Z
We investigate the quantum capacity of noisy quantum channels which can be represented by coupling a system to an effectively small environment. A capacity formula is derived for all cases where both system and environment are two-dimensional--including all extremal qubit channels. Similarly, for channels acting on higher dimensional systems we show that the capacity can be determined if the channel arises from a sufficiently small coupling to a qubit environment. Extensions to instances of channels with larger environment are provided and it is shown that bounds on the capacity with unconstrained environment can be obtained from decompositions into channels with small environment.
Remarks on twisted noncommutative quantum field theory
Zahn, Jochen [II. Institut fuer Theoretische Physik, Universitaet Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany)
2006-05-15T23:59:59.000Z
We review recent results on twisted noncommutative quantum field theory by embedding it into a general framework for the quantization of systems with a twisted symmetry. We discuss commutation relations in this setting and show that the twisted structure is so rigid that it is hard to derive any predictions, unless one gives up general principles of quantum theory. It is also shown that the twisted structure is not responsible for the presence or absence of UV/IR-mixing, as claimed in the literature.
Scaling Considerations in Ground State Quantum Computation
Ari Mizel; M. W. Mitchell; Marvin L. Cohen
2000-07-02T23:59:59.000Z
We study design challenges associated with realizing a ground state quantum computer. In such a computer, the energy gap between the ground state and first excited state must be sufficiently large to prevent disruptive excitations. Here, an estimate is provided of this gap as a function of computer size. We then address the problem of detecting the output of a ground state quantum computer. It is shown that the exponential detection difficulties that appear to be present at first can be overcome in a straightforward manner by small design changes.
Sylvia Bratzik; Silvestre Abruzzo; Hermann Kampermann; Dagmar Bruß
2013-03-14T23:59:59.000Z
We investigate quantum repeaters in the context of quantum key distribution. We optimize the secret key rate per memory per second with respect to different distillation protocols and distillation strategies. For this purpose, we also derive an analytical expression for the average number of entangled pairs created by the quantum repeater, including classical communication times for entanglement swapping and entanglement distillation. We investigate the impact of this classical communication time on the secret key rate. We finally study the effect of the detector efficiency on the secret key rate.
Quantum realism and quantum surrealism
Mateus Araújo
2014-08-29T23:59:59.000Z
In this thesis we explore the questions of what should be considered a "classical" theory, and which aspects of quantum theory cannot be captured by any theory that respects our intuition of classicality. This exploration is divided in two parts: in the first we review classical results of the literature, such as the Kochen-Specker theorem, von Neumann's theorem, Gleason's theorem, as well as more recent ideas, such as the distinction between $\\psi$-ontic and $\\psi$-epistemic ontological models, Spekkens' definition of contextuality, Hardy's ontological excess baggage theorem and the PBR theorem. The second part is concerned with pinning down what should be the "correct" definition of contextuality. We settle down on the definition advocated by Abramsky and Branderburger, motivated by the Fine theorem, and show the connection of this definition with the work of George Boole. This definition allows us to unify the notions of locality and noncontextuality, and use largely the same tools to characterize how quantum mechanics violates these notions of classicality. Exploring this formalism, we find a new family of noncontextuality inequalities. We conclude by reviewing the notion of state-independent contextuality.
A quantum speedup in machine learning: Finding a N-bit Boolean function for a classification
Seokwon Yoo; Jeongho Bang; Changhyoup Lee; Jinhyoung Lee
2014-10-14T23:59:59.000Z
We compare quantum and classical machines designed for learning an N-bit Boolean function in order to address how a quantum system improves the machine learning behavior. The machines of the two types consist of the same number of operations and control parameters, but only the quantum machines utilize the quantum coherence naturally induced by unitary operators. We show that quantum superposition enables quantum learning that is faster than classical learning by expanding the approximate solution regions, i.e., the acceptable regions. This is also demonstrated by means of numerical simulations with a standard feedback model, namely random search, and a practical model, namely differential evolution.
Probabilistic quantum phase-space simulation of Bell violations and their dynamical evolution
Laura Rosales-Zárate; Bogdan Opanchuk; Peter D. Drummond; Margaret D. Reid
2014-07-09T23:59:59.000Z
Quantum simulations of Bell inequality violations are numerically obtained using probabilistic phase space methods, namely the positive P-representation. In this approach the moments of quantum observables are evaluated as moments of variables that have values outside the normal eigenvalue range. There is thus a parallel with quantum weak measurements and weak values. Nevertheless, the representation is exactly equivalent to quantum mechanics. A number of states violating Bell inequalities are sampled, demonstrating that these quantum paradoxes can be treated with probabilistic methods. We treat quantum dynamics by simulating the time evolution of the Bell state formed via parametric down-conversion, and discuss multi-mode generalizations.
Farritor, Shane
Number: CFDA Number(s) - 93.243; Funding Opportunity Number - OA-08-002. Agency/Department: Department
Classification of macroscopic quantum effects
Tristan Farrow; Vlatko Vedral
2014-06-03T23:59:59.000Z
We review canonical experiments on systems that have pushed the boundary between the quantum and classical worlds towards much larger scales, and discuss their unique features that enable quantum coherence to survive. Because the types of systems differ so widely, we use a case by case approach to identifying the different parameters and criteria that capture their behaviour in a quantum mechanical framework. We find it helpful to categorise systems into three broad classes defined by mass, spatio-temporal coherence, and number of particles. The classes are not mutually exclusive and in fact the properties of some systems fit into several classes. We discuss experiments by turn, starting with interference of massive objects like macromolecules and micro-mechanical resonators, followed by self-interference of single particles in complex molecules, before examining the striking advances made with superconducting qubits. Finally, we propose a theoretical basis for quantifying the macroscopic features of a system to lay the ground for a more systematic comparison of the quantum properties in disparate systems.
Mingsheng Ying; Yuan Feng
2007-01-04T23:59:59.000Z
Loop is a powerful program construct in classical computation, but its power is still not exploited fully in quantum computation. The exploitation of such power definitely requires a deep understanding of the mechanism of quantum loop programs. In this paper, we introduce a general scheme of quantum loops and describe its computational process. The notions of termination and almost termination are proposed for quantum loops, and the function computed by a quantum loop is defined. To show their expressive power, quantum loops are applied in describing quantum walks. Necessary and sufficient conditions for termination and almost termination of a general quantum loop on any mixed input state are presented. A quantum loop is said to be (almost) terminating if it (almost) terminates on any input state. We show that a quantum loop is almost terminating if and only if it is uniformly almost terminating. It is observed that a small disturbance either on the unitary transformation in the loop body or on the measurement in the loop guard can make any quantum loop (almost) terminating. Moreover, a representation of the function computed by a quantum loop is given in terms of finite summations of matrices. To illustrate the notions and results obtained in this paper, two simplest classes of quantum loop programs, one qubit quantum loops, and two qubit quantum loops defined by controlled gates, are carefully examined.
Time-Energy Costs of Quantum Measurements
Chi-Hang Fred Fung; H. F. Chau
2014-05-08T23:59:59.000Z
Time and energy of quantum processes are a tradeoff against each other. We propose to ascribe to any given quantum process a time-energy cost to quantify how much computation it performs. Here, we analyze the time-energy costs for general quantum measurements, along a similar line as our previous work for quantum channels, and prove exact and lower bound formulae for the costs. We use these formulae to evaluate the efficiencies of actual measurement implementations. We find that one implementation for a Bell measurement is optimal in time-energy. We also analyze the time-energy cost for unambiguous state discrimination and find evidence that only a finite time-energy cost is needed to distinguish any number of states.
Quantum limits to estimation of photon deformation
Giovanni De Cillis; Matteo G. A. Paris
2014-07-08T23:59:59.000Z
We address potential deviations of radiation field from the bosonic behaviour and employ local quantum estimation theory to evaluate the ultimate bounds to precision in the estimation of these deviations using quantum-limited measurements on optical signals. We consider different classes of boson deformation and found that intensity measurement on coherent or thermal states would be suitable for their detection making, at least in principle, tests of boson deformation feasible with current quantum optical technology. On the other hand, we found that the quantum signal-to-noise ratio (QSNR) is vanishing with the deformation itself for all the considered classes of deformations and probe signals, thus making any estimation procedure of photon deformation inherently inefficient. A partial way out is provided by the polynomial dependence of the QSNR on the average number of photon, which suggests that, in principle, it would be possible to detect deformation by intensity measurements on high-energy thermal states.
Ideal Quantum Gases with Planck Scale Limitations
Collier, Rainer
2015-01-01T23:59:59.000Z
A thermodynamic system of non-interacting quantum particles changes its statistical distribution formulas if there is a universal limitation for the size of energetic quantum leaps (magnitude of quantum leaps smaller than Planck energy). By means of a restriction of the a priori equiprobability postulate one can reach a thermodynamic foundation of these corrected distribution formulas. The number of microstates is determined by means of a suitable counting method and combined with thermodynamics via the Boltzmann principle. The result is that, for particle energies that come close to the Planck energy, the thermodynamic difference between fermion and boson distribution vanishes. Both distributions then approximate a Boltzmann distribution. The wave and particle character of the quantum particles, too, can be influenced by choosing the size of the temperature and particle energy parameters relative to the Planck energy, as you can see from the associated fluctuation formulas. In the case of non-relativistic de...
Communication via entangled coherent quantum network
A. El Allati; Y. Hassouni; N. Metwally
2010-11-17T23:59:59.000Z
A quantum network is constructed via maximum entangled coherent states. The possibility of using this network to achieve communication between multi-participants is investigated. We showed that the probability of teleported unknown state successfully, depends on the size the used network. As the numbers of participants increases, the successful probability does not depend on the intensity of the field. The problem of implementing quantum teleportation protocol via a noise quantum network is discussed. We show one can send information perfectly with small values of the field intensity and larger values of the noise strength. The successful probability of this suggested protocol increases abruptly for larger values of the noise strength and gradually for small values. We show that for small size of the used quantum network, the fidelity of the teleported state decreases smoothly, while it decreases abruptly for larger size of network.
Quantum ratchet transport with minimal dispersion rate
Zhan, Fei; Ponomarev, A V; Hänggi, P
2011-01-01T23:59:59.000Z
We analyze the performance of quantum ratchets by considering the dynamics of an initially localized wave packet loaded into a flashing periodic potential. The directed center-of-mass motion can be initiated by the uniform modulation of the potential height, provided that the modulation protocol breaks all relevant time- and spatial reflection symmetries. A poor performance of quantum ratchet transport is characterized by a slow net motion and a fast diffusive spreading of the wave packet, while the desirable optimal performance is the contrary. By invoking a quantum analog of the classical P\\'eclet number, namely the quotient of the group velocity and the dispersion of the propagating wave packet, we calibrate the transport properties of flashing quantum ratchets and discuss the mechanisms that yield low-dispersive directed transport.
Quantum ratchet transport with minimal dispersion rate
Fei Zhan; S. Denisov; A. V. Ponomarev; P. Hänggi
2011-10-11T23:59:59.000Z
We analyze the performance of quantum ratchets by considering the dynamics of an initially localized wave packet loaded into a flashing periodic potential. The directed center-of-mass motion can be initiated by the uniform modulation of the potential height, provided that the modulation protocol breaks all relevant time- and spatial reflection symmetries. A poor performance of quantum ratchet transport is characterized by a slow net motion and a fast diffusive spreading of the wave packet, while the desirable optimal performance is the contrary. By invoking a quantum analog of the classical P\\'eclet number, namely the quotient of the group velocity and the dispersion of the propagating wave packet, we calibrate the transport properties of flashing quantum ratchets and discuss the mechanisms that yield low-dispersive directed transport.
Quantum Defect Theory for Cold Chemistry with Product Quantum State Resolution
Hazra, Jisha; Bohn, John L; Balakrishnan, N
2014-01-01T23:59:59.000Z
We present a formalism for cold and ultracold atom-diatom chemical reactions that combines a quantum close-coupling method at short-range with quantum defect theory at long-range. The method yields full state-to-state rovibrationally resolved cross sections as in standard close-coupling (CC) calculations but at a considerably less computational expense. This hybrid approach exploits the simplicity of MQDT while treating the short-range interaction explicitly using quantum CC calculations. The method, demonstrated for D+H$_2\\to$ HD+H collisions with rovibrational quantum state resolution of the HD product, is shown to be accurate for a wide range of collision energies and initial conditions. The hybrid CC-MQDT formalism may provide an alternative approach to full CC calculations for cold and ultracold reactions.
Princeton Plasma Physics Laboratory
these areas early with site surveys and as-builts Jun-2014 Titus open VU Negligible Low manager's experience= 25% VU= 5% R22 Revisions shown in pink. 86 Project Manager's Updated Number Affecte d Job Job Title Risk Description Mitigation Plan Corrective Action if Risk Occurs (task id if appl) Deadline to Retire
Quantum communication complexity advantage implies violation of a Bell inequality
Harry Buhrman; Lukasz Czekaj; Andrzej Grudka; Michal Horodecki; Pawel Horodecki; Marcin Markiewicz; Florian Speelman; Sergii Strelchuk
2015-02-03T23:59:59.000Z
We obtain a general connection between a quantum advantage in communication complexity and non-locality. We show that given any protocol offering a (sufficiently large) quantum advantage in communication complexity, there exists a way of obtaining measurement statistics which violate some Bell inequality. Our main tool is port-based teleportation. If the gap between quantum and classical communication complexity can grow arbitrarily large, the ratio of the quantum value to the classical value of the Bell quantity becomes unbounded with the increase in the number of inputs and outputs.
Quantum information becomes classical when distributed to many users
G. Chiribella; G. M. D'Ariano
2007-01-31T23:59:59.000Z
Any physical transformation that equally distributes quantum information over a large number M of users can be approximated by a classical broadcasting of measurement outcomes. The accuracy of the approximation is at least of the order 1/M. In particular, quantum cloning of pure and mixed states can be approximated via quantum state estimation. As an example, for optimal qubit cloning with 10 output copies, a single user has error probability p > 0.45 in distinguishing classical from quantum output--a value close to the error probability of the random guess.
Recycling of quantum information: Multiple observations of quantum systems
Peter Rapcan; John Calsamiglia; Ramon Munoz-Tapia; Emilio Bagan; Vladimir Buzek
2007-08-08T23:59:59.000Z
Given a finite number of copies of an unknown qubit state that have already been measured optimally, can one still extract any information about the original unknown state? We give a positive answer to this question and quantify the information obtainable by a given observer as a function of the number of copies in the ensemble, and of the number of independent observers that, one after the other, have independently measured the same ensemble of qubits before him. The optimality of the protocol is proven and extensions to other states and encodings are also studied. According to the general lore, the state after a measurement has no information about the state before the measurement. Our results manifestly show that this statement has to be taken with a grain of salt, specially in situations where the quantum states encode confidential information.
Photoconductivity of Si/Ge multilayer structures with Ge quantum dots pseudomorphic to the Si matrix
Talochkin, A. B., E-mail: tal@thermo.isp.nsc.ru; Chistokhin, I. B. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)
2011-07-15T23:59:59.000Z
Longitudinal photoconductivity spectra of Si/Ge multilayer structures with Ge quantum dots grown pseudomorphically to the Si matrix are studied. Lines of optical transitions between hole levels of quantum dots and Si electronic states are observed. This allowed us to construct a detailed energy-level diagram of electron-hole levels of the structure. It is shown that hole levels of pseudomorphic Ge quantum dots are well described by the simplest 'quantum box' model using actual sizes of Ge islands. The possibility of controlling the position of the long-wavelength photosensitivity edge by varying the growth parameters of Si/Ge structures with Ge quantum dots is determined.
Asymptotically Optimal Quantum Circuits for d-Level Systems
Bullock, Stephen S. [Mathematical and Computational Sciences Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8910 (United States); O'Leary, Dianne P. [Mathematical and Computational Sciences Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8910 (United States); Department of Computer Science and UMIACS, University of Maryland, College Park, Maryland 20742 (United States); Brennen, Gavin K. [Atomic Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8420 (United States)
2005-06-17T23:59:59.000Z
Scalability of a quantum computation requires that the information be processed on multiple subsystems. However, it is unclear how the complexity of a quantum algorithm, quantified by the number of entangling gates, depends on the subsystem size. We examine the quantum circuit complexity for exactly universal computation on many d-level systems (qudits). Both a lower bound and a constructive upper bound on the number of two-qudit gates result, proving a sharp asymptotic of {theta}(d{sup 2n}) gates. This closes the complexity question for all d-level systems (d finite). The optimal asymptotic applies to systems with locality constraints, e.g., nearest neighbor interactions.
Magic State Distillation and Gate Compilation in Quantum Algorithms for Quantum Chemistry
Colin J. Trout; Kenneth R. Brown
2015-01-29T23:59:59.000Z
Quantum algorithms for quantum chemistry map the dynamics of electrons in a molecule to the dynamics of a coupled spin system. To reach chemical accuracy for interesting molecules, a large number of quantum gates must be applied which implies the need for quantum error correction and fault-tolerant quantum computation. Arbitrary fault-tolerant operations can be constructed from a small, universal set of fault-tolerant operations by gate compilation. Quantum chemistry algorithms are compiled by decomposing the dynamics of the coupled spin-system using a Trotter formula, synthesizing the decomposed dynamics using Clifford operations and single-qubit rotations, and finally approximating the single-qubit rotations by a sequence of fault-tolerant single-qubit gates. Certain fault-tolerant gates rely on the preparation of specific single-qubit states referred to as magic states. As a result, gate compilation and magic state distillation are critical for solving quantum chemistry problems on a quantum computer. We review recent progress that has improved the efficiency of gate compilation and magic state distillation by orders of magnitude.
U. Alvarez-Rodriguez; M. Sanz; L. Lamata; E. Solano
2014-11-14T23:59:59.000Z
Addition plays a central role in mathematics and physics, while adders are ubiquitous devices in computation and electronics. In this sense, usual sum operations can be realized by classical Turing machines and also, with a suitable algorithm, by quantum Turing machines. Moreover, the sum of state vectors in the same Hilbert space, known as quantum superposition, is at the core of quantum physics. In fact, entanglement and the promised exponential speed-up of quantum computing are based on such superpositions. Here, we consider the existence of a quantum adder, defined as a unitary operation mapping two unknown quantum states encoded in different quantum systems onto their sum codified in a single one. The surprising answer is that this quantum adder is forbidden and it has the quantum cloning machine as a special case. This no-go result is of fundamental nature and its deep implications should be further studied.
Thermal Correlation Functions of Twisted Quantum Fields
Prasad Basu; Rahul Srivastava; Sachindeo Vaidya
2010-04-08T23:59:59.000Z
We derive the thermal correlators for twisted quantum fields on noncommutative spacetime. We show that the thermal expectation value of the number operator is same as in commutative spacetime, but that higher correlators are sensitive to the noncommutativity parameters $\\theta^{\\mu\
Thermal correlation functions of twisted quantum fields
Basu, Prasad; Srivastava, Rahul; Vaidya, Sachindeo [Centre for High Energy Physics, Indian Institute of Science, Bangalore, 560012 (India)
2010-07-15T23:59:59.000Z
We derive the thermal correlators for twisted quantum fields on noncommutative spacetime. We show that the thermal expectation value of the number operator is same as in commutative spacetime, but that higher correlators are sensitive to the noncommutativity parameters {theta}{sup {mu}{nu}.}
Quantum Gates for Superconducting A Dissertation
Devoret, Michel H.
, and the minimal number of non-linear circuit elements are particularly interesting, as they would reduce from Fourier analysis of the circuit Hamiltonian in a partic- ular multiply-rotating reference frame with the electromagnetic modes of an engineered quantum circuit. Doing so requires the subtle application of control
Systematic quantum corrections to screening in thermonuclear fusion
Shirish M. Chitanvis
2006-06-13T23:59:59.000Z
We develop a series expansion of the plasma screening length away from the classical limit in powers of $\\hbar^{2}$. It is shown that the leading order quantum correction increases the screening length in solar conditions by approximately 2% while it decreases the fusion rate by approximately $ 0.34%$. We also calculate the next higher order quantum correction which turns out to be approximately 0.05%.
Systematic quantum corrections to screening in thermonuclear fusion
Chitanvis, S M
2006-01-01T23:59:59.000Z
We develop a series expansion of the plasma screening length away from the classical limit in powers of $\\hbar^{2}$. It is shown that the leading order quantum correction increases the screening length in solar conditions by approximately 2% while it decreases the fusion rate by approximately $ 0.34%$. We also calculate the next higher order quantum correction which turns out to be approximately 0.05%.
Twists of quantum groups and noncommutative field theory
P. P. Kulish
2006-06-07T23:59:59.000Z
The role of quantum universal enveloping algebras of symmetries in constructing a noncommutative geometry of space-time and corresponding field theory is discussed. It is shown that in the framework of the twist theory of quantum groups, the noncommutative (super) space-time defined by coordinates with Heisenberg commutation relations, is (super) Poincar\\'e invariant, as well as the corresponding field theory. Noncommutative parameters of global transformations are introduced.
Quantum thermodynamics of general quantum processes
Felix C. Binder; Sai Vinjanampathy; Kavan Modi; John Goold
2015-03-27T23:59:59.000Z
Accurately describing work extraction from a quantum system is a central objective for the extension of thermodynamics to individual quantum systems. The concepts of work and heat are surprisingly subtle when generalizations are made to arbitrary quantum states. We formulate an operational thermodynamics suitable for application to an open quantum system undergoing quantum evolution under a general quantum process by which we mean a completely-positive and trace-preserving map. We derive an operational first law of thermodynamics for such processes and show consistency with the second law. We show that heat, from the first law, is positive when the input state of the map majorises the output state. Moreover, the change in entropy is also positive for the same majorisation condition. This makes a strong connection between the two operational laws of thermodynamics.
Gordon Chalmers; Olaf Lechtenfeld; Bernd Niemeyer
2000-09-08T23:59:59.000Z
We calculate the genus-one three- and four-point amplitudes in the 2+2 dimensional closed N=(2,2) worldsheet supersymmetric string within the RNS formulation. Vertex operators are redefined with the incorporation of spinor helicity techniques, and the quantum scattering is shown to be manifestly gauge and Lorentz invariant after normalizing the string states. The continuous spin structure summation over the monodromies of the worldsheet fermions is carried out explicitly, and the field-theory limit is extracted. The amplitude in this limit is shown to be the maximally helicity violating amplitude in pure gravity evaluated in a two-dimensional setting, which vanishes, unlike the four-dimensional result. The vanishing of the genus-one N=2 closed string amplitude is related to the absence of one-loop divergences in dimensionally regulated IIB supergravity. Comparisons and contrasts between self-dual field theory and the N=2 string theory are made at the quantum level; they have different S-matrices. Finally, we point to further relations with self-dual field theory and two-dimensional models.
Jacques Arnaud; Laurent Chusseau; Fabrice Philippe
2003-06-02T23:59:59.000Z
Quantum heat engines employ as working agents multi-level systems instead of gas-filled cylinders. We consider particularly two-level agents such as electrons immersed in a magnetic field. Work is produced in that case when the electrons are being carried from a high-magnetic-field region into a low-magnetic-field region. In watermills, work is produced instead when some amount of fluid drops from a high-altitude reservoir to a low-altitude reservoir. We show that this purely mechanical engine may in fact be considered as a two-level quantum heat engine, provided the fluid is viewed as consisting of n molecules of weight one and N-n molecules of weight zero. Weight-one molecules are analogous to electrons in their higher energy state, while weight-zero molecules are analogous to electrons in their lower energy state. More generally, fluids consist of non-interacting molecules of various weights. It is shown that, not only the average value of the work produced per cycle, but also its fluctuations, are the same for mechanical engines and quantum (Otto) heat engines. The reversible Carnot cycles are approached through the consideration of multiple sub-reservoirs.
Unsharp eigenvalues and quantum contextuality
F. De Zela
2014-10-01T23:59:59.000Z
The Kochen-Specker theorem, Bell inequalities, and several other tests that were designed to rule out hidden-variable theories, assume the existence of observables having infinitely sharp eigenvalues. A paradigmatic example is spin-1/2. It is measured with a Stern-Gerlach array whose outputs are divided into two classes, spin-up and spin-down, in correspondence to the two spots observed on a detection screen. The spot's finite size is attributed to imperfections of the measuring device. This assumption turns the experimental output into a dichotomic, discrete one, thereby allowing the assignment of each spot to an infinitely sharp eigenvalue. Alternatively, one can assume that the spot's finite size stems from eigenvalues spanning a continuous range. Can we disprove such an assumption? Can we rule out hidden-variable theories that reproduce quantum predictions by assuming that, e.g., the electron's magnetic moment is not exactly the same for all electrons? We address these questions by focusing on the Peres-Mermin version of the Bell-Kochen-Specker theorem. It is shown that the assumption of unsharp eigenvalues precludes ruling out non-contextual hidden-variable theories and hence quantum contextuality does not arise. Analogous results hold for Bell-like inequalities. This represents a new loophole that spoils several fundamental tests of quantum mechanics and issues the challenge to close it.
Quantum Storage of a Photonic Polarization Qubit in a Solid
Mustafa Gündo?an; Patrick M. Ledingham; Attaallah Almasi; Matteo Cristiani; Hugues de Riedmatten
2012-01-20T23:59:59.000Z
We report on the quantum storage and retrieval of photonic polarization quantum bits onto and out of a solid state storage device. The qubits are implemented with weak coherent states at the single photon level, and are stored for 500 ns in a praseodymium doped crystal with a storage and retrieval efficiency of 10%, using the atomic frequency comb scheme. We characterize the storage by using quantum state tomography, and find that the average conditional fidelity of the retrieved qubits exceeds 95% for a mean photon number mu=0.4. This is significantly higher than a classical benchmark, taking into account the Poissonian statistics and finite memory efficiency, which proves that our device functions as a quantum storage device for polarization qubits, even if tested with weak coherent states. These results extend the storage capabilities of solid state quantum memories to polarization encoding, which is widely used in quantum information science.
Strategy for quantum algorithm design assisted by machine learning
Jeongho Bang; Junghee Ryu; Seokwon Yoo; Marcin Pawlowski; Jinhyoung Lee
2014-07-17T23:59:59.000Z
We propose a method for quantum algorithm design assisted by machine learning. The method uses a quantum-classical hybrid simulator, where a "quantum student" is being taught by a "classical teacher." In other words, in our method, the learning system is supposed to evolve into a quantum algorithm for a given problem assisted by classical main-feedback system. Our method is applicable to design quantum oracle-based algorithm. As a case study, we chose an oracle decision problem, called a Deutsch-Jozsa problem. We showed by using Monte-Carlo simulations that our simulator can faithfully learn quantum algorithm to solve the problem for given oracle. Remarkably, learning time is proportional to the square root of the total number of parameters instead of the exponential dependance found in the classical machine learning based method.
David Viennot; Lucile Aubourg
2014-11-19T23:59:59.000Z
We study a theoretical model of closed quasi-hermitian chain of spins which exhibits quantum analogues of chimera states, i.e. long life classical states for which a part of an oscillator chain presents an ordered dynamics whereas another part presents a disordered chaotic dynamics. For the quantum analogue, the chimera behavior deals with the entanglement between the spins of the chain. We discuss the entanglement properties, quantum chaos, quantum disorder and semi-classical similarity of our quantum chimera system. The quantum chimera concept is novel and induces new perspectives concerning the entanglement of multipartite systems.
Quantum Evolution and Anticipation
Hans-Rudolf Thomann
2010-03-04T23:59:59.000Z
In a previous paper we have investigated quantum states evolving into mutually orthogonal states at equidistant times, and the quantum anticipation effect exhibited by measurements at one half step. Here we extend our analyzes of quantum anticipation to general type quantum evolutions and spectral measures and prove that quantum evolutions possessing an embedded orthogonal evolution are characterized by positive joint spectral measure. Furthermore, we categorize quantum evolution, assess anticipation strength and provide a framework of analytic tools and results, thus preparing for further investigation and experimental verification of anticipation in concrete physical situations such as the H-atom, which we have found to exhibit anticipation.
The concrete theory of numbers: initial numbers and wonderful properties of numbers repunit
Boris V. Tarasov
2007-04-07T23:59:59.000Z
In this work initial numbers and repunit numbers have been studied. All numbers have been considered in a decimal notation. The problem of simplicity of initial numbers has been studied. Interesting properties of numbers repunit are proved: $gcd(R_a, R_b) = R_{gcd(a,b)}$; $R_{ab}/(R_aR_b)$ is an integer only if $gcd(a,b) = 1$, where $a\\geq1$, $b\\geq1$ are integers. Dividers of numbers repunit, are researched by a degree of prime number.
Nucleon semimagic numbers and low-energy neutron scattering
D. A. Zaikin; I. V. Surkova
2010-04-09T23:59:59.000Z
It is shown that experimental values of the cross sections of inelastic low-energy neutron scattering on even-even nuclei together with the description of these cross sections in the framework of the coupled channel optical model may be considered as a reliable method for finding nuclei with a semimagic number (or numbers) of nucleons. Some examples of the application of this method are considered.
Robert Carroll
2007-11-05T23:59:59.000Z
We show some relations between Ricci flow and quantum theory via Fisher information and the quantum potential.
Satellite-Based Quantum Communications
Hughes, Richard J [Los Alamos National Laboratory; Nordholt, Jane E [Los Alamos National Laboratory; McCabe, Kevin P [Los Alamos National Laboratory; Newell, Raymond T [Los Alamos National Laboratory; Peterson, Charles G [Los Alamos National Laboratory
2010-09-20T23:59:59.000Z
Single-photon quantum communications (QC) offers the attractive feature of 'future proof', forward security rooted in the laws of quantum physics. Ground based quantum key distribution (QKD) experiments in optical fiber have attained transmission ranges in excess of 200km, but for larger distances we proposed a methodology for satellite-based QC. Over the past decade we have devised solutions to the technical challenges to satellite-to-ground QC, and we now have a clear concept for how space-based QC could be performed and potentially utilized within a trusted QKD network architecture. Functioning as a trusted QKD node, a QC satellite ('QC-sat') could deliver secret keys to the key stores of ground-based trusted QKD network nodes, to each of which multiple users are connected by optical fiber or free-space QC. A QC-sat could thereby extend quantum-secured connectivity to geographically disjoint domains, separated by continental or inter-continental distances. In this paper we describe our system concept that makes QC feasible with low-earth orbit (LEO) QC-sats (200-km-2,000-km altitude orbits), and the results of link modeling of expected performance. Using the architecture that we have developed, LEO satellite-to-ground QKD will be feasible with secret bit yields of several hundred 256-bit AES keys per contact. With multiple ground sites separated by {approx} 100km, mitigation of cloudiness over any single ground site would be possible, potentially allowing multiple contact opportunities each day. The essential next step is an experimental QC-sat. A number of LEO-platforms would be suitable, ranging from a dedicated, three-axis stabilized small satellite, to a secondary experiment on an imaging satellite. to the ISS. With one or more QC-sats, low-latency quantum-secured communications could then be provided to ground-based users on a global scale. Air-to-ground QC would also be possible.
From Quantum Information to Gravitation (in German)
Thomas Görnitz
2009-04-11T23:59:59.000Z
To unite quantum theory and general relativity, in a new access it is shown that from a theory of an abstract quantum information - called Protyposis - the theory of general relativity can be deduced by means of few and physically good founded reasons. "Abstract" quantum information means that primarily no special meaning is connected with it. The resulting cosmology has an isotropic and homogeneous metric and solves the so-called cosmological problems. For the Protyposis it follows an equation of states for energy density and pressure that fulfils all the energy conditions and that also gives an explanation for the dark energy. If it is demanded that the relations between spacetime structure and the material contend also hold for deviations from this ideal cosmology than General relativity results as a description for local inhomogenities.
The Time's Arrow within the Uncertainty Quantum
Zhen Wang
1998-06-22T23:59:59.000Z
A generalized framework is developed which uses a set description instead of wavefunction to emphasize the role of the observer. Such a framework is found to be very effective in the study of the measurement problem and time's arrow. Measurement in classical and quantum theory is given a unified treatment. With the introduction of the concept of uncertainty quantum which is the basic unit of measurement, we show that the time's arrow within the uncertainty quantum is just opposite to the time's arrow in the observable reality. A special constant is discussed which explains our sensation of time and provides a permanent substrate for all change. It is shown that the whole spacetime connects together in a delicate structure.
Efficient Quantum Filtering for Quantum Feedback Control
Pierre Rouchon; Jason F. Ralph
2015-01-06T23:59:59.000Z
We discuss an efficient numerical scheme for the recursive filtering of diffusive quantum stochastic master equations. We show that the resultant quantum trajectory is robust and may be used for feedback based on inefficient measurements. The proposed numerical scheme is amenable to approximation, which can be used to further reduce the computational burden associated with calculating quantum trajectories and may allow real-time quantum filtering. We provide a two-qubit example where feedback control of entanglement may be within the scope of current experimental systems.
Magnetic field control of the intraband optical absorption in two-dimensional quantum rings
Olendski, O., E-mail: oolendski@ksu.edu.sa [King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box 2454, Riyadh 11451 (Saudi Arabia); Barakat, T., E-mail: tbarakat@ksu.edu.sa [Department of Physics, King Saud University, P.O. Box 2454, Riyadh 11451 (Saudi Arabia)
2014-02-28T23:59:59.000Z
Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency is calculated as a function of the magnetic field and levels' broadening.
Statistical analysis of sampling methods in quantum tomography
Thomas Kiesel
2012-06-07T23:59:59.000Z
In quantum physics, all measured observables are subject to statistical uncertainties, which arise from the quantum nature as well as the experimental technique. We consider the statistical uncertainty of the so-called sampling method, in which one estimates the expectation value of a given observable by empirical means of suitable pattern functions. We show that if the observable can be written as a function of a single directly measurable operator, the variance of the estimate from the sampling method equals to the quantum mechanical one. In this sense, we say that the estimate is on the quantum mechanical level of uncertainty. In contrast, if the observable depends on non-commuting operators, e.g. different quadratures, the quantum mechanical level of uncertainty is not achieved. The impact of the results on quantum tomography is discussed, and different approaches to quantum tomographic measurements are compared. It is shown explicitly for the estimation of quasiprobabilities of a quantum state, that balanced homodyne tomography does not operate on the quantum mechanical level of uncertainty, while the unbalanced homodyne detection does.
Impossibility of secure cloud quantum computing for classical client
Tomoyuki Morimae; Takeshi Koshiba
2014-07-07T23:59:59.000Z
The first generation quantum computer will be implemented in the cloud style, since only few groups will be able to access such an expensive and high-maintenance machine. How the privacy of the client can be protected in such a cloud quantum computing? It was theoretically shown [A. Broadbent, J. F. Fitzsimons, and E. Kashefi, Proceedings of the 50th Annual IEEE Symposium on Foundation of Computer Science, 517 (2009)], and experimentally demonstrated [S. Barz, E. Kashefi, A. Broadbent, J. F. Fitzsimons, A. Zeilinger, and P. Walther, Science {\\bf335}, 303 (2012)] that a client who can generate randomly-rotated single qubit states can delegate her quantum computing to a remote quantum server without leaking any privacy. The generation of a single qubit state is not too much burden for the client, and therefore we can say that "almost classical client" can enjoy the secure cloud quantum computing. However, isn't is possible to realize a secure cloud quantum computing for a client who is completely free from any quantum technology? Here we show that perfectly-secure cloud quantum computing is impossible for a completely classical client unless classical computing can simulate quantum computing, or a breakthrough is brought in classical cryptography.
Reconstructing the profile of time-varying magnetic fields with quantum sensors
Magesan, Easwar
Quantum systems have shown great promise for precision metrology thanks to advances in their control. This has allowed not only the sensitive estimation of external parameters but also the reconstruction of their temporal ...
Investigating puzzling aspects of the quantum theory by means of its hydrodynamic formulation
Sanz, A S
2015-01-01T23:59:59.000Z
Bohmian mechanics, a hydrodynamic formulation of the quantum theory, constitutes a useful resource to analyze the role of the phase as the mechanism responsible for the dynamical evolution of quantum systems. Here this role is discussed in the context of quantum interference. Specifically, it is shown that when dealing with two wave-packet coherent superpositions this phenomenon is analogous to an effective collision of a single wave packet with a barrier. This effect is illustrated by means of a numerical simulation of Young's two-slit experiment. Furthermore, outcomes from this analysis are also applied to a realistic simulation of Wheeler's delayed choice experiment. As it is shown, in both cases the Bohmian formulation helps to understand in a natural way (and, therefore, to demystify) what are typically regarded as paradoxical aspects of the quantum theory, simply stressing the important dynamical role played by the quantum phase. Accordingly, our conception of quantum systems should not rely on artifici...
Reduction of Quantum Phase Fluctuations Implies Antibunching of Photon
Prakash Gupta; Anirban Pathak
2007-01-25T23:59:59.000Z
A clear physical meaning of the Carruthers-Nieto symmetric quantum phase fluctuation parameter (U) has been provided in Susskind Glogower and Barnett Pegg formalism of quantum phase and it is shown that the reduction of phase fluctuation parameter U with respect to its coherent state value corresponds to an antibunched state. Thus nonclassicality of a state may be manifested through the phase fluctuation parameters. As examples, quantum phase fluctuations in different optical processes, such as four wave mixing, six wave mixing and second harmonic generation have been studied by using Carruthers-Nieto quantum phase fluctuation parameters. The operators required for the calculation of quantum phase fluctuations are expressed in closed analytical forms (up to second order in coupling constant). It is also found that the reduction of phase fluctuations compared to their initial values are possible in all three cases which means nonclassical (antibunched) state exists in all these cases.
Universal Characteristics of Fractal Fluctuations in Prime Number Distribution
A. M. Selvam
2008-11-12T23:59:59.000Z
The frequency of occurrence of prime numbers at unit number spacing intervals exhibits selfsimilar fractal fluctuations concomitant with inverse power law form for power spectrum generic to dynamical systems in nature such as fluid flows, stock market fluctuations, population dynamics, etc. The physics of long-range correlations exhibited by fractals is not yet identified. A recently developed general systems theory visualises the eddy continuum underlying fractals to result from the growth of large eddies as the integrated mean of enclosed small scale eddies, thereby generating a hierarchy of eddy circulations, or an inter-connected network with associated long-range correlations. The model predictions are as follows: (i) The probability distribution and power spectrum of fractals follow the same inverse power law which is a function of the golden mean. The predicted inverse power law distribution is very close to the statistical normal distribution for fluctuations within two standard deviations from the mean of the distribution. (ii) Fractals signify quantumlike chaos since variance spectrum represents probability density distribution, a characteristic of quantum systems such as electron or photon. (ii) Fractal fluctuations of frequency distribution of prime numbers signify spontaneous organisation of underlying continuum number field into the ordered pattern of the quasiperiodic Penrose tiling pattern. The model predictions are in agreement with the probability distributions and power spectra for different sets of frequency of occurrence of prime numbers at unit number interval for successive 1000 numbers. Prime numbers in the first 10 million numbers were used for the study.
Quantum Process Tomography by 2D Fluorescence Spectroscopy
Leonardo A. Pachon; Andrew H. Marcus; Alan Aspuru-Guzik
2015-02-09T23:59:59.000Z
Reconstruction of the dynamics (quantum process tomography) of the single-exciton manifold in energy transfer systems is proposed here on the basis of two-dimensional fluorescence spectroscopy (2D-FS) with phase-modulation. The quantum-process-tomography protocol introduced here benefits from, e.g., the sensitivity enhancement and signal-to-noise ratio ascribed to 2D-FS. Although the isotropically averaged spectroscopic signals depend on the quantum yield parameter $\\Gamma$ of the doubly-excited-exciton manifold, it is shown that the reconstruction of the dynamics is insensitive to this parameter. Applications to foundational and applied problems, as well as further extensions, are discussed.
Quantum Process Tomography by 2D Fluorescence Spectroscopy
Pachon, Leonardo A; Aspuru-Guzik, Alan
2015-01-01T23:59:59.000Z
Reconstruction of the dynamics (quantum process tomography) of the single-exciton manifold in energy transfer systems is proposed here on the basis of two-dimensional fluorescence spectroscopy (2D-FS) with phase-modulation. The quantum-process-tomography protocol introduced here benefits from, e.g., the sensitivity enhancement and signal-to-noise ratio ascribed to 2D-FS. Although the isotropically averaged spectroscopic signals depend on the quantum yield parameter $\\Gamma$ of the doubly-excited-exciton manifold, it is shown that the reconstruction of the dynamics is insensitive to this parameter. Applications to foundational and applied problems, as well as further extensions, are discussed.
Quantum Mirrors and Crossing Symmetry as Heart of Ghost Imaging
D. B. Ion; M. L. Ion; L. Rusu
2009-04-27T23:59:59.000Z
In this paper it is proved that the key to understanding the ghost imaging mystery are the crossing symmetric photon reactions in the nonlinear media. Hence, the laws of the plane quantum mirror (QM) and that of spherical quantum mirror, observed in the ghost imaging experiments, are obtained as natural consequences of the energy-momentum conservation laws. So, it is shown that the ghost imaging laws depend only on the energy-momentum conservation and not on the photons entanglement. The extension of these results to the ghost imaging with other kind of light is discussed. Some fundamental experiments for a decisive tests of the [SPDC-DFG]-quantum mirror are suggested.
Reversing the Weak Quantum Measurement for a Photonic Qubit
Yong-Su Kim; Young-Wook Cho; Young-Sik Ra; Yoon-Ho Kim
2009-03-18T23:59:59.000Z
We demonstrate the conditional reversal of a weak (partial-collapse) quantum measurement on a photonic qubit. The weak quantum measurement causes a nonunitary transformation of a qubit which is subsequently reversed to the original state after a successful reversing operation. Both the weak measurement and the reversal operation are implemented linear optically. The state recovery fidelity, determined by quantum process tomography, is shown to be over 94% for partial-collapse strength up to 0.9. We also experimentally study information gain due to the weak measurement and discuss the role of the reversing operation as an information erasure.
Passive decoy-state quantum key distribution with practical light sources
Curty, Marcos [ETSI Telecomunicacion, Department of Signal Theory and Communications, University of Vigo, Campus Universitario, E-36310 Vigo (Pontevedra) (Spain); Ma, Xiongfeng [Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, N2L 3G1 Waterloo, Ontario (Canada); Qi, Bing [Center for Quantum Information and Quantum Control, Department of Physics and Department of Electrical and Computer Engineering, University of Toronto, M5S 3G4 Toronto, Ontario (Canada); Moroder, Tobias [Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, N2L 3G1 Waterloo, Ontario (Canada); Quantum Information Theory Group, Institute of Theoretical Physics I, University of Erlangen-Nuernberg, D-91058 Erlangen (Germany); Max Planck Institute for the Science of Light, D-91058 Erlangen (Germany)
2010-02-15T23:59:59.000Z
Decoy states have been proven to be a very useful method for significantly enhancing the performance of quantum key distribution systems with practical light sources. Although active modulation of the intensity of the laser pulses is an effective way of preparing decoy states in principle, in practice passive preparation might be desirable in some scenarios. Typical passive schemes involve parametric down-conversion. More recently, it has been shown that phase-randomized weak coherent pulses (WCP) can also be used for the same purpose [M. Curty et al., Opt. Lett. 34, 3238 (2009).] This proposal requires only linear optics together with a simple threshold photon detector, which shows the practical feasibility of the method. Most importantly, the resulting secret key rate is comparable to the one delivered by an active decoy-state setup with an infinite number of decoy settings. In this article we extend these results, now showing specifically the analysis for other practical scenarios with different light sources and photodetectors. In particular, we consider sources emitting thermal states, phase-randomized WCP, and strong coherent light in combination with several types of photodetectors, like, for instance, threshold photon detectors, photon number resolving detectors, and classical photodetectors. Our analysis includes as well the effect that detection inefficiencies and noise in the form of dark counts shown by current threshold detectors might have on the final secret key rate. Moreover, we provide estimations on the effects that statistical fluctuations due to a finite data size can have in practical implementations.
Generalized concatenated quantum codes
Grassl, Markus
We discuss the concept of generalized concatenated quantum codes. This generalized concatenation method provides a systematical way for constructing good quantum codes, both stabilizer codes and nonadditive codes. Using ...
Quantum convolutional stabilizer codes
Chinthamani, Neelima
2004-09-30T23:59:59.000Z
Quantum error correction codes were introduced as a means to protect quantum information from decoherance and operational errors. Based on their approach to error control, error correcting codes can be divided into two different classes: block codes...
Friedenauer, Axel; Glückert, Jan Tibor; Porras, Diego; Schätz, Tobias
2008-01-01T23:59:59.000Z
To gain deeper insight into the dynamics of complex quantum systems we need a quantum leap in computer simulations. We can not translate quantum behaviour arising with superposition states or entanglement efficiently into the classical language of conventional computers. The final solution to this problem is a universal quantum computer [1], suggested in 1982 and envisioned to become functional within the next decade(s); a shortcut was proposed via simulating the quantum behaviour of interest in a different quantum system, where all parameters and interactions can be controlled and the outcome detected sufficiently well. Here we study the feasibility of a quantum simulator based on trapped ions [2]. We experimentally simulate the adiabatic evolution of the smallest non-trivial spin system from the paramagnetic into the (anti-)ferromagnetic order with a quantum magnetisation for two spins of 98%, controlling and manipulating all relevant parameters of the Hamiltonian independently via electromagnetic fields. W...
Svetlichny, George
2011-01-01T23:59:59.000Z
I contemplate the idea that the subjective world and quantum state reductions are one and the same. If true, this resolves with one stroke both the quantum mechanical measurement problem and the hard problem of consciousness.
George Svetlichny
2011-04-13T23:59:59.000Z
I contemplate the idea that the subjective world and quantum state reductions are one and the same. If true, this resolves with one stroke both the quantum mechanical measurement problem and the hard problem of consciousness.
Ran Gelles; Tal Mor
2007-11-25T23:59:59.000Z
Theoretical quantum key distribution (QKD) protocols commonly rely on the use of qubits (quantum bits). In reality, however, due to practical limitations, the legitimate users are forced to employ a larger quantum (Hilbert) space, say a quhexit (quantum six-dimensional) space, or even a much larger quantum Hilbert space. Various specific attacks exploit of these limitations. Although security can still be proved in some very special cases, a general framework that considers such realistic QKD protocols, as well as} attacks on such protocols, is still missing. We describe a general method of attacking realistic QKD protocols, which we call the `quantum-space attack'. The description is based on assessing the enlarged quantum space actually used by a protocol, the `quantum space of the protocol'. We demonstrate these new methods by classifying various (known) recent attacks against several QKD schemes, and by analyzing a novel attack on interferometry-based QKD.
Highlighting the mechanism of the quantum speedup by time-symmetric and relational quantum mechanics
Giuseppe Castagnoli
2014-12-11T23:59:59.000Z
Bob hides a ball in one of four drawers. Alice is to locate it. Classically she has to open up to three drawers, quantally just one. The fundamental reason for this quantum speedup is not known. We explain it by extending the usual representation of the quantum algorithm, limited to the process of solving the problem, to the process of setting the problem. The number of the drawer with the ball becomes a unitary transformation of the random outcome of the preparation measurement. This brings in relational quantum mechanics: the extension is with respect to Bob and cannot be with respect to Alice. It would tell her the drawer number before she opens any drawer. To Alice, the projection of the quantum state due to the preparation measurement should be retarded at the end of her search; in the input state of the search, the drawer number is determined to Bob and undetermined to Alice. A second consequence is the emergence of an ambiguity. Either the preparation measurement or the final one required to read the solution selects the solution. For reasons of symmetry, we assume that the selection shares evenly between the two measurements. All is as if Alice, by reading the solution, selected half of the information that specifies the drawer number. This selection leaves the input state to Bob unaltered and projects that to Alice on a state of lower entropy where she knows that half in advance. The quantum algorithm is a sum over histories in each of which Alice knows in advance that the ball is in a pair of drawers and locates it by opening one of the two. More in general, given an oracle problem, this explanation of the speedup predicts the number of queries required to solve it in an optimal quantum way.
Fair and optimistic quantum contract signing
Paunkovic, N.; Mateus, P. [SQIG - Instituto de Telecomunicacoes, IST, TULisbon, Avenida Rovisco Pais, P-1049-001 Lisbon (Portugal); Bouda, J. [Faculty of Informatics, Masaryk University, Botanicka 68a, CZ-60200 Brno (Czech Republic)
2011-12-15T23:59:59.000Z
We present a fair and optimistic quantum-contract-signing protocol between two clients that requires no communication with the third trusted party during the exchange phase. We discuss its fairness and show that it is possible to design such a protocol for which the probability of a dishonest client to cheat becomes negligible and scales as N{sup -1/2}, where N is the number of messages exchanged between the clients. Our protocol is not based on the exchange of signed messages: Its fairness is based on the laws of quantum mechanics. Thus, it is abuse free, and the clients do not have to generate new keys for each message during the exchange phase. We discuss a real-life scenario when measurement errors and qubit-state corruption due to noisy channels and imperfect quantum memories occur and argue that for a real, good-enough measurement apparatus, transmission channels, and quantum memories, our protocol would still be fair. Apart from stable quantum memories, the other segments of our protocol could be implemented by today's technology, as they require in essence the same type of apparatus as the one needed for the Bennett-Brassard 1984 (BB84) cryptographic protocol. Finally, we briefly discuss two alternative versions of the protocol, one that uses only two states [based on the Bennett 1992 (B92) protocol] and the other that uses entangled pairs, and show that it is possible to generalize our protocol to an arbitrary number of clients.
Quantum process tomography with coherent states
Saleh Rahimi-Keshari; Artur Scherer; Ady Mann; Ali T. Rezakhani; A. I. Lvovsky; Barry C. Sanders
2010-09-17T23:59:59.000Z
We develop an enhanced technique for characterizing quantum optical processes based on probing unknown quantum processes only with coherent states. Our method substantially improves the original proposal [M. Lobino et al., Science 322, 563 (2008)], which uses a filtered Glauber-Sudarshan decomposition to determine the effect of the process on an arbitrary state. We introduce a new relation between the action of a general quantum process on coherent state inputs and its action on an arbitrary quantum state. This relation eliminates the need to invoke the Glauber-Sudarshan representation for states; hence it dramatically simplifies the task of process identification and removes a potential source of error. The new relation also enables straightforward extensions of the method to multi-mode and non-trace-preserving processes. We illustrate our formalism with several examples, in which we derive analytic representations of several fundamental quantum optical processes in the Fock basis. In particular, we introduce photon-number cutoff as a reasonable physical resource limitation and address resource vs accuracy trade-off in practical applications. We show that the accuracy of process estimation scales inversely with the square root of photon-number cutoff.
Features of the electronic spectrum in a type-I core - shell quantum dot
Igoshina, S E; Karmanov, A A [Penza State University, Penza (Russian Federation)
2013-01-31T23:59:59.000Z
The model is proposed, which allows one to solve the problem of finding the energy spectrum and the wave function of an electron in a type-I core - shell quantum dot. It is shown that the size of the core and shell can serve as control parameters for the optimisation of the energy structure of the quantum dot in order to obtain the real structures with desired electrophysical and optical properties. (quantum dots)
Pang, Shuo
2008-10-10T23:59:59.000Z
S coating. The CdSe/Zns core/shell quantum dots are prepared colloidally via organometallic synthesis. In these experiments, green quantum dots with an emission peak at 530nm are used. The absorption and emission spectra are shown in Figure 9. 23... WHISPERING GALLERY MODES IN QUANTUM DOT-EMBEDDED DIELECTRIC MICROSPHERES FOR TAGLESS REMOTE REFRACTOMETRIC SENSING A Thesis by SHUO PANG Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment...
Broadband tunability of gain-flattened quantum well semiconductor lasers with an external grating
Mittelstein, M.; Mehuys, D.; Yariv, A.; Ungar, J.E.; Sarfaty, R.
1989-03-20T23:59:59.000Z
Quantum well lasers are shown to exhibit flattened broadband gain spectra at a particular pumping condition. The gain requirement for a grating-tuned external cavity configuration is examined and applied to a semiconductor quantum well laser with an optimized length of gain region. The predicted very broadband tunability of quantum well lasers is confirmed experimentally by grating-tuning of uncoated lasers over 85 nm, with single longitudinal mode output power exceeding 200 mW.
Efficient bounds on quantum-communication rates via their reduced variants
Nowakowski, Marcin L.; Horodecki, Pawel [Faculty of Applied Physics and Mathematics, Gdansk University of Technology, PL-80-952 Gdansk, Poland and National Quantum Information Centre of Gdansk, Andersa 27, PL-81-824 Sopot (Poland)
2010-10-15T23:59:59.000Z
We investigate one-way communication scenarios where Bob operating on his component can transfer some subsystem to the environment. We define reduced versions of quantum-communication rates and, further, prove upper bounds on a one-way quantum secret key, distillable entanglement, and quantum-channel capacity by means of their reduced versions. It is shown that in some cases they drastically improve their estimation.
Particle creation and particle number in an expanding universe
Leonard Parker
2012-05-25T23:59:59.000Z
I describe the logical basis of the method that I developed in 1962 and 1963 to define a quantum operator corresponding to the observable particle number of a quantized free scalar field in a spatially-flat isotropically expanding (and/or contracting) universe. This work also showed for the first time that particles were created from the vacuum by the curved space-time of an expanding spatially-flat FLRW universe. The same process is responsible for creating the nearly scale-invariant spectrum of quantized perturbations of the inflaton scalar field during the inflationary stage of the expansion of the universe. I explain how the method that I used to obtain the observable particle number operator involved adiabatic invariance of the particle number (hence, the name adiabatic regularization) and the quantum theory of measurement of particle number in an expanding universe. I also show how I was led in a surprising way, to the discovery in 1964 that there would be no particle creation by these spatially-flat FLRW universes for free fields of any integer or half-integer spin satisfying field equations that are invariant under conformal transformations of the metric. The methods I used to define adiabatic regularization for particle number, were based on generally-covariant concepts like adiabatic invariance and measurement that were fundamental and determined results that were unique to each given adiabatic order.
Jae-Suk Park; John Terilla; Thomas Tradler
2009-09-21T23:59:59.000Z
We introduce the concept of a quantum background and a functor QFT. In the case that the QFT moduli space is smooth formal, we construct a flat quantum superconnection on a bundle over QFT which defines algebraic structures relevant to correlation functions in quantum field theory. We go further and identify chain level generalizations of correlation functions which should be present in all quantum field theories.
Generalized Concatenated Quantum Codes
Markus Grassl; Peter Shor; Graeme Smith; John Smolin; Bei Zeng
2009-01-09T23:59:59.000Z
We introduce the concept of generalized concatenated quantum codes. This generalized concatenation method provides a systematical way for constructing good quantum codes, both stabilizer codes and nonadditive codes. Using this method, we construct families of new single-error-correcting nonadditive quantum codes, in both binary and nonbinary cases, which not only outperform any stabilizer codes for finite block length, but also asymptotically achieve the quantum Hamming bound for large block length.
Nano-wires with surface disorder: Giant localization lengths and quantum-to-classical crossover
J. Feist; A. Bäcker; R. Ketzmerick; S. Rotter; B. Huckestein; J. Burgdörfer
2006-09-14T23:59:59.000Z
We investigate electronic quantum transport through nano-wires with one-sided surface roughness. A magnetic field perpendicular to the scattering region is shown to lead to exponentially diverging localization lengths in the quantum-to-classical crossover regime. This effect can be quantitatively accounted for by tunneling between the regular and the chaotic components of the underlying mixed classical phase space.
Acceleration of positrons by a relativistic electron beam in the presence of quantum effects
Niknam, A. R. [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran (Iran, Islamic Republic of)] [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran (Iran, Islamic Republic of); Aki, H.; Khorashadizadeh, S. M. [Physics Department, Birjand University, Birjand (Iran, Islamic Republic of)] [Physics Department, Birjand University, Birjand (Iran, Islamic Republic of)
2013-09-15T23:59:59.000Z
Using the quantum magnetohydrodynamic model and obtaining the dispersion relation of the Cherenkov and cyclotron waves, the acceleration of positrons by a relativistic electron beam is investigated. The Cherenkov and cyclotron acceleration mechanisms of positrons are compared together. It is shown that growth rate and, therefore, the acceleration of positrons can be increased in the presence of quantum effects.
Fluctuation theorems for quantum master equations Massimiliano Esposito* and Shaul Mukamel
Mukamel, Shaul
equation--i.e., a quantum master equation QME . Quantum trajectories and their associated entropy, heat extended to stochastic dynamics 2 . It relates the distribu- tion of the work done by a driving force relation has recently been shown to hold for arbi- trary coupling strength between the system
Data Compression with Prime Numbers
Gordon Chalmers
2005-11-16T23:59:59.000Z
A compression algorithm is presented that uses the set of prime numbers. Sequences of numbers are correlated with the prime numbers, and labeled with the integers. The algorithm can be iterated on data sets, generating factors of doubles on the compression.
Thermodynamics of discrete quantum processes
Janet Anders; Vittorio Giovannetti
2012-11-01T23:59:59.000Z
We define thermodynamic configurations and identify two primitives of discrete quantum processes between configurations for which heat and work can be defined in a natural way. This allows us to uncover a general second law for any discrete trajectory that consists of a sequence of these primitives, linking both equilibrium and non-equilibrium configurations. Moreover, in the limit of a discrete trajectory that passes through an infinite number of configurations, i.e. in the reversible limit, we recover the saturation of the second law. Finally, we show that for a discrete Carnot cycle operating between four configurations one recovers Carnot's thermal efficiency.
Fourier Transform Quantum State Tomography
Mohammadreza Mohammadi; Agata M. Branczyk; Daniel F. V. James
2013-01-17T23:59:59.000Z
We propose a technique for performing quantum state tomography of photonic polarization-encoded multi-qubit states. Our method uses a single rotating wave plate, a polarizing beam splitter and two photon-counting detectors per photon mode. As the wave plate rotates, the photon counters measure a pseudo-continuous signal which is then Fourier transformed. The density matrix of the state is reconstructed using the relationship between the Fourier coefficients of the signal and the Stokes' parameters that represent the state. The experimental complexity, i.e. different wave plate rotation frequencies, scales linearly with the number of qubits.
Quantum weak chaos in a degenerate system
V. Ya. Demikhovskii; D. I. Kamenev; G. A. Luna-Acosta
1998-09-27T23:59:59.000Z
Quantum weak chaos is studied in a perturbed degenerate system --- a charged particle interacting with a monochromatic wave in a transverse magnetic field. The evolution operator for an arbitrary number of periods of the external field is built and its structure is explored in terms of the QE (quasienergy eigenstates) under resonance condition (wave frequency $=$ cyclotron frequency) in the regime of weak classical chaos. The new phenomenon of diffusion via the quantum separatrices and the influence of chaos on diffusion are investigated and, in the quasi classical limit, compared with its classical dynamics. We determine the crossover from purely quantum diffusion to a diffusion which is the quantum manifestation of classical diffusion along the stochastic web. This crossover results from the non-monotonic dependence of the characteristic localization length of the QE states on the wave amplitude. The width of the quantum separatrices was computed and compared with the width of the classical stochastic web. We give the physical parameters which can be realized experimentally to show the manifestation of quantum chaos in nonlinear acoustic resonance.
Quantum model of microcavity intersubband electroluminescent devices
Simone De Liberato; Cristiano Ciuti
2008-04-28T23:59:59.000Z
We present a quantum theoretical analysis of the electroluminescence from an intersubband transition of a quantum well structure embedded in a planar microcavity. By using a cluster factorization method, we have derived a closed set of dynamical equations for the quantum well carrier and cavity photon occupation numbers, the correlation between the cavity field and the intersubband polarization, as well as polarization-polarization contributions. In order to model the electrical excitation, we have considered electron population tunneling from an injector and into an extractor contact. The tunneling rates have been obtained by considering the bare electronic states in the quantum well and the limit of validity of this approximation (broad-band injection) are discussed in detail. We apply the present quantum model to provide a comprehensive description of the electronic transport and optical properties of an intersubband microcavity light emitting diode, accounting for non-radiative carrier relaxation and Pauli blocking. We study the enhancement of the electroluminescence quantum efficiency passing from the weak to the strong polariton coupling regime.
Topological Quantum Distillation
H. Bombin; M. A. Martin-Delgado
2007-03-29T23:59:59.000Z
We construct a class of topological quantum codes to perform quantum entanglement distillation. These codes implement the whole Clifford group of unitary operations in a fully topological manner and without selective addressing of qubits. This allows us to extend their application also to quantum teleportation, dense coding and computation with magic states.
Matthew James
2014-06-20T23:59:59.000Z
This paper explains some fundamental ideas of {\\em feedback} control of quantum systems through the study of a relatively simple two-level system coupled to optical field channels. The model for this system includes both continuous and impulsive dynamics. Topics covered in this paper include open and closed loop control, impulsive control, optimal control, quantum filtering, quantum feedback networks, and coherent feedback control.
Quantum Computing Computer Scientists
Yanofsky, Noson S.
of Vector Spaces 3 The Leap From Classical to Quantum 3.1 Classical Deterministic Systems 3.2 ClassicalQuantum Computing for Computer Scientists Noson S. Yanofsky and Mirco A. Mannucci #12;© May 2007 Noson S. Yanofsky Mirco A. Mannucci #12;Quantum Computing for Computer Scientists Noson S. Yanofsky
Randall Espinoza; Tom Imbo; Paul Lopata
2004-03-30T23:59:59.000Z
We investigate an entangled deformation of the deterministic quantum cloning process, called enscription, that can be applied to (certain) sets of distinct quantum states which are not necessarily orthogonal, called texts. Some basic theorems on enscribable texts are given, and a relationship to probabilistic quantum cloning is demonstrated.
Giulio Chiribella; Giacomo Mauro D'Ariano; Paolo Perinotti
2007-12-09T23:59:59.000Z
We present a method for optimizing quantum circuits architecture. The method is based on the notion of "quantum comb", which describes a circuit board in which one can insert variable subcircuits. The method allows one to efficiently address novel kinds of quantum information processing tasks, such as storing-retrieving, and cloning of channels.
Quantum chaos in quantum Turing machines
Ilki Kim; Guenter Mahler
1999-10-18T23:59:59.000Z
We investigate a 2-spin quantum Turing architecture, in which discrete local rotations \\alpha_m of the Turing head spin alternate with quantum controlled NOT-operations. We demonstrate that a single chaotic parameter input \\alpha_m leads to a chaotic dynamics in the entire Hilbert-space.
Vacuum energy: quantum hydrodynamics vs quantum gravity
G. E. Volovik
2005-09-09T23:59:59.000Z
We compare quantum hydrodynamics and quantum gravity. They share many common features. In particular, both have quadratic divergences, and both lead to the problem of the vacuum energy, which in the quantum gravity transforms to the cosmological constant problem. We show that in quantum liquids the vacuum energy density is not determined by the quantum zero-point energy of the phonon modes. The energy density of the vacuum is much smaller and is determined by the classical macroscopic parameters of the liquid including the radius of the liquid droplet. In the same manner the cosmological constant is not determined by the zero-point energy of quantum fields. It is much smaller and is determined by the classical macroscopic parameters of the Universe dynamics: the Hubble radius, the Newton constant and the energy density of matter. The same may hold for the Higgs mass problem: the quadratically divergent quantum correction to the Higgs potential mass term is also cancelled by the microscopic (trans-Planckian) degrees of freedom due to thermodynamic stability of the whole quantum vacuum.
Entanglement, number fluctuations and optimized interferometric phase measurement
Q. Y. He; T. G. Vaughan; P. D. Drummond; M. D. Reid
2012-06-14T23:59:59.000Z
We derive a phase-entanglement criterion for two bosonic modes which is immune to number fluc- tuations, using the generalized Moore-Penrose inverse to normalize the phase-quadrature operator. We also obtain a phase-squeezing criterion that is immune to number fluctuations using similar techniques. These are utilized to obtain an operational definition of relative phase-measurement sensitivity, via analysis of phase measurement in interferometry. We show that these measures are proportional to enhanced phase-measurement sensitivity. The phase-entanglement criterion is a hallmark for a new type of quantum squeezing, namely planar quantum squeezing. This has the property that it squeezes two orthogonal spin directions simultaneously, which is possible owing to the fact that the SU(2) group that describes spin symmetry has a three-dimensional parameter space, of higher dimension than the group for photonic quadratures. The practical advantage of planar quantum squeezing is that, unlike conventional spin-squeezing, it allows noise reduction over all phase-angles simultaneously. The application of this type of squeezing is to quantum measure- ment of an unknown phase. We show that a completely unknown phase requires two orthogonal measurements, and that with planar quantum squeezing it is possible to reduce the measurement uncertainty independently of the unknown phase value. This is a different type of squeezing to the usual spin-squeezing interferometric criterion, which is only applicable when the measured phase is already known to a good approximation, or can be measured iteratively. As an example, we calcu- late the phase-entanglement of the ground state of a two-well, coupled Bose-Einstein condensate, similar to recent experiments. This system demonstrates planar squeezing in both the attractive and repulsive interaction regimes.
On the explanation for quantum statistics
Simon Saunders
2005-11-15T23:59:59.000Z
The concept of classical indistinguishability is analyzed and defended against a number of well-known criticisms, with particular attention to the Gibbs' paradox. Granted that it is as much at home in classical as in quantum statistical mechanics, the question arises as to why indistinguishability, in quantum mechanics but not in classical mechanics, forces a change in statistics. The answer, illustrated with simple examples, is that the equilibrium measure on classical phase space is continuous, whilst on Hilbert space it is discrete. The relevance of names, or equivalently, properties stable in time that can be used as names, is also discussed.
Achievable Qubit Rates for Quantum Information Wires
Hulya Yadsan-Appleby; Tobias J. Osborne
2011-02-15T23:59:59.000Z
Suppose Alice and Bob have access to two separated regions, respectively, of a system of electrons moving in the presence of a regular one-dimensional lattice of binding atoms. We consider the problem of communicating as much quantum information, as measured by the qubit rate, through this quantum information wire as possible. We describe a protocol whereby Alice and Bob can achieve a qubit rate for these systems which is proportional to N^(-1/3) qubits per unit time, where N is the number of lattice sites. Our protocol also functions equally in the presence of interactions modelled via the t-J and Hubbard models.
Exchange effects in magnetized quantum plasmas
Trukhanova, Mariya Iv
2015-01-01T23:59:59.000Z
We apply the many-particle quantum hydrodynamics including the Coulomb exchange interaction to magnetized quantum plasmas. We consider a number of wave phenomenon under influence of the Coulomb exchange interaction. Since the Coulomb exchange interaction affects longitudinal and transverse-longitudinal waves we focus our attention to the Langmuir waves, Trivelpiece-Gould waves, ion-acoustic waves in non-isothermal magnetized plasmas, the dispersion of the longitudinal low-frequency ion-acoustic waves and low-frequencies electromagnetic waves at $T_{e}\\gg T_{i}$ . We obtained the numerical simulation of the dispersion properties of different types of waves.
Trading classical and quantum computational resources
Sergey Bravyi; Graeme Smith; John Smolin
2015-06-03T23:59:59.000Z
We propose examples of a hybrid quantum-classical simulation where a classical computer assisted by a small quantum processor can efficiently simulate a larger quantum system. First we consider sparse quantum circuits such that each qubit participates in O(1) two-qubit gates. It is shown that any sparse circuit on n+k qubits can be simulated by sparse circuits on n qubits and a classical processing that takes time $2^{O(k)} poly(n)$. Secondly, we study Pauli-based computation (PBC) where allowed operations are non-destructive eigenvalue measurements of n-qubit Pauli operators. The computation begins by initializing each qubit in the so-called magic state. This model is known to be equivalent to the universal quantum computer. We show that any PBC on n+k qubits can be simulated by PBCs on n qubits and a classical processing that takes time $2^{O(k)} poly(n)$. Finally, we propose a purely classical algorithm that can simulate a PBC on n qubits in a time $2^{c n} poly(n)$ where $c\\approx 0.94$. This improves upon the brute-force simulation method which takes time $2^n poly(n)$. Our algorithm exploits the fact that n-fold tensor products of magic states admit a low-rank decomposition into n-qubit stabilizer states.
Quantum like modelling of the non-separability of voters' preferences in the U.S. political system
Polina Khrennikova
2014-05-07T23:59:59.000Z
Divided Government is nowadays a common feature of the U.S. political system. The voters can cast partisan ballots for two political powers the executive (Presidential elections) and the legislative (the Congress election). Some recent studies have shown that many voters tend to shape their preferences for the political parties by choosing different parties in these two election contests. This type of behavior referred to by Smith et al. (1999) as "ticket splitting" shows irrationality of behavior (such as preference reversal) from the perspective of traditional decision making theories (Von Neumann and Morgenstern (1953), Savage, (1954)). It has been shown by i.e. Zorn and Smith (2011) and also Khrennikova et al. (2014) that these types of "non-separable" preferences are context dependent and can be well accommodated in a quantum like framework. In this paper we use data from Smith et al. (1999) to show first of all probabilistic violation of classical (Kolmogorovian) framework. We proceed with the depiction of our observables (the Congress and the Presidential contexts) with the aid of the quantum probability formula that incorporates the "contextuality" of the decision making process through the interference term. Statistical data induces an interference term of large magnitude a so called hyperbolic interference. We perform with help of our transition probabilities a state reconstruction of the voters state vectors to test for the applicability of the generalized Born rule. This state can be mathematically represented in the generalized Hilbert space based on hyper-complex numbers.
Properties of Reactive Oxygen Species by Quantum Monte Carlo
Andrea Zen; Bernhardt L. Trout; Leonardo Guidoni
2014-06-16T23:59:59.000Z
The electronic properties of the oxygen molecule, in its singlet and triplet states, and of many small oxygen-containing radicals and anions have important roles in different fields of Chemistry, Biology and Atmospheric Science. Nevertheless, the electronic structure of such species is a challenge for ab-initio computational approaches because of the difficulties to correctly describe the statical and dynamical correlation effects in presence of one or more unpaired electrons. Only the highest-level quantum chemical approaches can yield reliable characterizations of their molecular properties, such as binding energies, equilibrium structures, molecular vibrations, charge distribution and polarizabilities. In this work we use the variational Monte Carlo (VMC) and the lattice regularized Monte Carlo (LRDMC) methods to investigate the equilibrium geometries and molecular properties of oxygen and oxygen reactive species. Quantum Monte Carlo methods are used in combination with the Jastrow Antisymmetrized Geminal Power (JAGP) wave function ansatz, which has been recently shown to effectively describe the statical and dynamical correlation of different molecular systems. In particular we have studied the oxygen molecule, the superoxide anion, the nitric oxide radical and anion, the hydroxyl and hydroperoxyl radicals and their corresponding anions, and the hydrotrioxyl radical. Overall, the methodology was able to correctly describe the geometrical and electronic properties of these systems, through compact but fully-optimised basis sets and with a computational cost which scales as $N^3-N^4$, where $N$ is the number of electrons. This work is therefore opening the way to the accurate study of the energetics and of the reactivity of large and complex oxygen species by first principles.
Mario G. Silveirinha
2014-06-09T23:59:59.000Z
Here, we develop a comprehensive quantum theory for the phenomenon of quantum friction. Based on a theory of macroscopic quantum electrodynamics for unstable systems, we calculate the quantum expectation of the friction force, and link the friction effect to the emergence of system instabilities related to the Cherenkov effect. These instabilities may occur due to the hybridization of particular guided modes supported by the individual moving bodies, and selection rules for the interacting modes are derived. It is proven that the quantum friction effect can take place even when the interacting bodies are lossless and made of nondispersive dielectrics.
Quantum Operation Time Reversal
Crooks, Gavin E.
2008-03-25T23:59:59.000Z
The dynamics of an open quantum system can be described by a quantum operation: A linear, complete positive map of operators. Here, I exhibit a compact expression for the time reversal of a quantum operation, which is closely analogous to the time reversal of a classical Markov transition matrix. Since open quantum dynamics are stochastic, and not, in general, deterministic, the time reversal is not, in general, an inversion of the dynamics. Rather, the system relaxes toward equilibrium in both the forward and reverse time directions. The probability of a quantum trajectory and the conjugate, time reversed trajectory are related by the heat exchanged with the environment.
Quantum Physics and Nanotechnology
Vladimir K. Nevolin
2011-06-06T23:59:59.000Z
Experimental studies of infinite (unrestricted at least in one direction) quantum particle motion using probe nanotechnologies have revealed the necessity of revising previous concepts of their motion. Particularly, quantum particles transfer quantum motion nonlocality energy beside classical kinetic energy, in other words, they are in two different kinds of motion simultaneously. The quantum component of the motion energy may be quite considerable under certain circumstances. Some new effects were predicted and proved experimentally in terms of this phenomenon. A new prototype refrigerating device was tested, its principle of operation being based on the effect of transferring the quantum component of the motion energy.
Quantum ballistic evolution in quantum mechanics: Application to quantum computers
Benioff, P. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
1996-08-01T23:59:59.000Z
Quantum computers are important examples of processes whose evolution can be described in terms of iterations of single-step operators or their adjoints. Based on this, Hamiltonian evolution of processes with associated step operators {ital T} is investigated here. The main limitation of this paper is to processes which evolve quantum ballistically, i.e., motion restricted to a collection of nonintersecting or distinct paths on an arbitrary basis. The main goal of this paper is proof of a theorem which gives necessary and sufficient conditions that {ital T} must satisfy so that there exists a Hamiltonian description of quantum ballistic evolution for the process, namely, that {ital T} is a partial isometry and is orthogonality preserving and stable on some basis. Simple examples of quantum ballistic evolution for quantum Turing machines with one and with more than one type of elementary step are discussed. It is seen that for nondeterministic machines the basis set can be quite complex with much entanglement present. It is also proven that, given a step operator {ital T} for an arbitrary {ital deterministic} quantum Turing machine, it is decidable if {ital T} is stable and orthogonality preserving, and if quantum ballistic evolution is possible. The proof fails if {ital T} is a step operator for a {ital nondeterministic} machine. It is an open question if such a decision procedure exists for nondeterministic machines. This problem does not occur in classical mechanics. Also the definition of quantum Turing machines used here is compared with that used by other authors. {copyright} {ital 1996 The American Physical Society.}
Quantum Geometry and Black Holes
G., J Fernando Barbero
2015-01-01T23:59:59.000Z
We present an overall picture of the advances in the description of black hole physics from the perspective of loop quantum gravity. After an introduction that discusses the main conceptual issues we present some details about the classical and quantum geometry of isolated horizons and their quantum geometry and then use this scheme to give a natural definition of the entropy of black holes. The entropy computations can be neatly expressed in the form of combinatorial problems solvable with the help of methods based on number theory and the use of generating functions. The recovery of the Bekenstein-Hawking law and corrections to it is explained in some detail. After this, due attention is paid to the discussion of semiclassical issues. An important point in this respect is the proper interpretation of the horizon area as the energy that should appear in the statistical-mechanical treatment of the black hole model presented here. The chapter ends with a comparison between the microscopic and semiclassical app...
Hugo Garcia-Compean; Oscar Loaiza-Brito; Aldo Martinez-Merino; Roberto Santos-Silva
2013-10-27T23:59:59.000Z
By wrapping D3-branes over 3-cycles on a half-flat manifold we construct an effective supersymmetric black hole in the N=2 low-energy theory in four-dimensions. Specifically we find that the torsion cycles present in a half-flat compactification, corresponding to the mirror symmetric image of electric NS flux on a Calabi-Yau manifold, manifest in the half-flat black hole as quantum hair. We compute the electric and magnetic charges related to the quantum hair, and also the mass contribution to the effective black hole. We find that by wrapping a number of D3-branes equal to the order of the discrete group associated to the torsional part of the half-flat homology, the effective charge and mass terms vanishes. We compute the variation of entropy and the corresponding temperature associated with the lost of quantum hair. We also comment on the equivalence between canceling Freed-Witten anomaly and the assumption of self-duality for the 5-form field strength. Finally from a K-theoretical perspective, we compute the presence of discrete RR charge of D-branes wrapping torsional cycles in a half-flat manifold.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Bacon, Dave; Flammia, Steven T.; Crosswhite, Gregory M.
2013-06-01T23:59:59.000Z
We describe a many-body quantum system that can be made to quantum compute by the adiabatic application of a large applied field to the system. Prior to the application of the field, quantum information is localized on one boundary of the device, and after the application of the field, this information propagates to the other side of the device, with a quantum circuit applied to the information. The applied circuit depends on the many-body Hamiltonian of the material, and the computation takes place in a degenerate ground space with symmetry-protected topological order. Such “adiabatic quantum transistors” are universal adiabatic quantum computing devices that have the added benefit of being modular. Here, we describe this model, provide arguments for why it is an efficient model of quantum computing, and examine these many-body systems in the presence of a noisy environment.
Adiabatic topological quantum computing
Chris Cesare; Andrew J. Landahl; Dave Bacon; Steven T. Flammia; Alice Neels
2014-06-10T23:59:59.000Z
Topological quantum computing promises error-resistant quantum computation without active error correction. However, there is a worry that during the process of executing quantum gates by braiding anyons around each other, extra anyonic excitations will be created that will disorder the encoded quantum information. Here we explore this question in detail by studying adiabatic code deformations on Hamiltonians based on topological codes, notably Kitaev's surface codes and the more recently discovered color codes. We develop protocols that enable universal quantum computing by adiabatic evolution in a way that keeps the energy gap of the system constant with respect to the computation size and introduces only simple local Hamiltonian interactions. This allows one to perform holonomic quantum computing with these topological quantum computing systems. The tools we develop allow one to go beyond numerical simulations and understand these processes analytically.
Trajectories without quantum uncertainties
Eugene S. Polzik; Klemens Hammerer
2014-05-13T23:59:59.000Z
A common knowledge suggests that trajectories of particles in quantum mechanics always have quantum uncertainties. These quantum uncertainties set by the Heisenberg uncertainty principle limit precision of measurements of fields and forces, and ultimately give rise to the standard quantum limit in metrology. With the rapid developments of sensitivity of measurements these limits have been approached in various types of measurements including measurements of fields and acceleration. Here we show that a quantum trajectory of one system measured relatively to the other "reference system" with an effective negative mass can be quantum uncertainty--free. The method crucially relies on the generation of an Einstein-Podolsky-Rosen entangled state of two objects, one of which has an effective negative mass. From a practical perspective these ideas open the way towards force and acceleration measurements at new levels of sensitivity far below the standard quantum limit.
The Computational Limit to Quantum Determinism and the Black Hole Information Loss Paradox
Arkady Bolotin
2015-06-08T23:59:59.000Z
The present paper scrutinizes the principle of quantum determinism, which maintains that the complete information about the initial quantum state of a physical system should determine the system's quantum state at any other time. As it shown in the paper, assuming the strong exponential time hypothesis, SETH, which conjectures that known algorithms for solving computational NP-complete problems (often brute-force algorithms) are optimal, the quantum deterministic principle cannot be used generally, i.e., for randomly selected physical systems, particularly macroscopic systems. In other words, even if the initial quantum state of an arbitrary system were precisely known, as long as SETH is true it might be impossible in the real world to predict the system's exact final quantum state. The paper suggests that the breakdown of quantum determinism in a process, in which a black hole forms and then completely evaporates, might actually be physical evidence supporting SETH.
Quantum Thermodynamic Cycles and Quantum Heat Engines (II)
H. T. Quan
2009-03-09T23:59:59.000Z
We study the quantum mechanical generalization of force or pressure, and then we extend the classical thermodynamic isobaric process to quantum mechanical systems. Based on these efforts, we are able to study the quantum version of thermodynamic cycles that consist of quantum isobaric process, such as quantum Brayton cycle and quantum Diesel cycle. We also consider the implementation of quantum Brayton cycle and quantum Diesel cycle with some model systems, such as single particle in 1D box and single-mode radiation field in a cavity. These studies lay the microscopic (quantum mechanical) foundation for Szilard-Zurek single molecule engine.
Direct Sum Theorem for Bounded Round Quantum Communication Complexity
Dave Touchette
2014-09-15T23:59:59.000Z
We prove a direct sum theorem for bounded round entanglement-assisted quantum communication complexity. To do so, we use the fully quantum definition for information cost and complexity that we recently introduced, and use both the fact that information is a lower bound on the communication, and the fact that a direct sum property holds for quantum information complexity. We then give a protocol for compressing a single copy of a protocol down to its quantum information cost, up to terms depending on the number of rounds and the allowed increase in error. Two important tools to derive this protocol are a smooth conditional min-entropy bound for a one-shot quantum state redistribution protocol, and the quantum substate theorem of Jain, Radhakrishnan and Sen (FOCS'02) to transform this bound into a von Neumann conditional entropy bound. This result further establishes the newly introduced notions of quantum information cost and complexity as the correct quantum generalisations of the classical ones in the standard communication complexity setting. Finding such a quantum generalization of information complexity was one of the open problem recently raised by Braverman (STOC'12).
Universal Single-Server Blind Quantum Computation for Classical Client
Hai-Ru Xu; Bang-Hai Wang
2014-11-12T23:59:59.000Z
Blind quantum computation allows a client without enough quantum technologies to delegate her quantum computation to quantum server, while keeping her input, output and algorithm secure. In this paper, we propose a universal single-server and classical-client blind quantum computation protocol based on entanglement swapping technology. In our protocol, the client interface with only one server and the only ability of the client requires is to get particles from trusted center and forward them to the server. Moreover, the protocol can be modified to make client completely classical by improving the ability of the trusted center. Numbers of blind quantum computation protocols have been presented in recent years, including single-, double- and triple-server protocols. In the single-server protocol, client needs to prepare single qubits. Though client can be classical in the double-server protocol, the two servers, who share Bell state from trusted center, are not allowed to communicate with each other. Recently, the triple-server protocol solves the noncommunication problem. Three servers, however, make the implementation of the computation sophisticated and unrealistic. Since it is impossible for blind quantum computation with only classical client and single server, blind quantum computation may work in the "Cloud + E-commerce" style in the future. Our protocol might become a key ingredient for real-life application in the first generation of quantum computations.
All-Optical Switching Using the Quantum Zeno Effect and Two-Photon Absorption
B. C. Jacobs; J. D. Franson
2009-05-08T23:59:59.000Z
We have previously shown that the quantum Zeno effect can be used to implement quantum logic gates for quantum computing applications, where the Zeno effect was produced using a strong two-photon absorbing medium. Here we show that the Zeno effect can also be used to implement classical logic gates whose inputs and outputs are high-intensity fields (coherent states). The operation of the devices can be understood using a quasi-static analysis, and their switching times are calculated using a dynamic approach. The two-photon absorption coefficient of rubidium vapor is shown to allow operation of these devices at relatively low power levels.
Small numbers in supersymmetric theories of nature
Graesser, Michael L.
1999-05-01T23:59:59.000Z
The Standard Model of particle interactions is a successful theory for describing the interactions of quarks, leptons and gauge bosons at microscopic distance scales. Despite these successes, the theory contains many unsatisfactory features. The origin of particle masses is a central mystery that has eluded experimental elucidation. In the Standard Model the known particles obtain their mass from the condensate of the so-called Higgs particle. Quantum corrections to the Higgs mass require an unnatural fine tuning in the Higgs mass of one part in 10{sup {minus}32} to obtain the correct mass scale of electroweak physics. In addition, the origin of the vast hierarchy between the mass scales of the electroweak and quantum gravity physics is not explained in the current theory. Supersymmetric extensions to the Standard Model are not plagued by this fine tuning issue and may therefore be relevant in Nature. In the minimal supersymmetric Standard Model there is also a natural explanation for electroweak symmetry breaking. Supersymmetric Grand Unified Theories also correctly predict a parameter of the Standard Model. This provides non-trivial indirect evidence for these theories. The most general supersymmetric extension to the Standard Model however, is excluded by many physical processes, such as rare flavor changing processes, and the non-observation of the instability of the proton. These processes provide important information about the possible structure such a theory. In particular, certain parameters in this theory must be rather small. A physics explanation for why this is the case would be desirable. It is striking that the gauge couplings of the Standard Model unify if there is supersymmetry close to the weak scale. This suggests that at high energies Nature is described by a supersymmetric Grand Unified Theory. But the mass scale of unification must be introduced into the theory since it does not coincide with the probable mass scale of strong quantum gravity. The subject of this dissertation is both the phenomenology and model-building opportunities that may lie behind the small numbers that appear in supersymmetric extensions of the Standard Model.
D'Ariano, Giacomo Mauro [QUIT Group, Dipartimento di Fisica 'A. Volta', 27100 Pavia (Italy) and Center for Photonic Communication and Computing, Northwestern University, Evanston, IL 60208 (Italy)
2010-05-04T23:59:59.000Z
I will argue that the proposal of establishing operational foundations of Quantum Theory should have top-priority, and that the Lucien Hardy's program on Quantum Gravity should be paralleled by an analogous program on Quantum Field Theory (QFT), which needs to be reformulated, notwithstanding its experimental success. In this paper, after reviewing recently suggested operational 'principles of the quantumness', I address the problem on whether Quantum Theory and Special Relativity are unrelated theories, or instead, if the one implies the other. I show how Special Relativity can be indeed derived from causality of Quantum Theory, within the computational paradigm 'the universe is a huge quantum computer', reformulating QFT as a Quantum-Computational Field Theory (QCFT). In QCFT Special Relativity emerges from the fabric of the computational network, which also naturally embeds gauge invariance. In this scheme even the quantization rule and the Planck constant can in principle be derived as emergent from the underlying causal tapestry of space-time. In this way Quantum Theory remains the only theory operating the huge computer of the universe.Is the computational paradigm only a speculative tautology (theory as simulation of reality), or does it have a scientific value? The answer will come from Occam's razor, depending on the mathematical simplicity of QCFT. Here I will just start scratching the surface of QCFT, analyzing simple field theories, including Dirac's. The number of problems and unmotivated recipes that plague QFT strongly motivates us to undertake the QCFT project, since QCFT makes all such problems manifest, and forces a re-foundation of QFT.
Compendium of Experimental Cetane Numbers
Yanowitz, J.; Ratcliff, M. A.; McCormick, R. L.; Taylor, J. D.; Murphy, M. J.
2014-08-01T23:59:59.000Z
This report is an updated version of the 2004 Compendium of Experimental Cetane Number Data and presents a compilation of measured cetane numbers for pure chemical compounds. It includes all available single compound cetane number data found in the scientific literature up until March 2014 as well as a number of unpublished values, most measured over the past decade at the National Renewable Energy Laboratory. This Compendium contains cetane values for 389 pure compounds, including 189 hydrocarbons and 201 oxygenates. More than 250 individual measurements are new to this version of the Compendium. For many compounds, numerous measurements are included, often collected by different researchers using different methods. Cetane number is a relative ranking of a fuel's autoignition characteristics for use in compression ignition engines; it is based on the amount of time between fuel injection and ignition, also known as ignition delay. The cetane number is typically measured either in a single-cylinder engine or a constant volume combustion chamber. Values in the previous Compendium derived from octane numbers have been removed, and replaced with a brief analysis of the correlation between cetane numbers and octane numbers. The discussion on the accuracy and precision of the most commonly used methods for measuring cetane has been expanded and the data has been annotated extensively to provide additional information that will help the reader judge the relative reliability of individual results.
Beni Yoshida
2011-04-03T23:59:59.000Z
Searches for possible new quantum phases and classifications of quantum phases have been central problems in physics. Yet, they are indeed challenging problems due to the computational difficulties in analyzing quantum many-body systems and the lack of a general framework for classifications. While frustration-free Hamiltonians, which appear as fixed point Hamiltonians of renormalization group transformations, may serve as representatives of quantum phases, it is still difficult to analyze and classify quantum phases of arbitrary frustration-free Hamiltonians exhaustively. Here, we address these problems by sharpening our considerations to a certain subclass of frustration-free Hamiltonians, called stabilizer Hamiltonians, which have been actively studied in quantum information science. We propose a model of frustration-free Hamiltonians which covers a large class of physically realistic stabilizer Hamiltonians, constrained to only three physical conditions; the locality of interaction terms, translation symmetries and scale symmetries, meaning that the number of ground states does not grow with the system size. We show that quantum phases arising in two-dimensional models can be classified exactly through certain quantum coding theoretical operators, called logical operators, by proving that two models with topologically distinct shapes of logical operators are always separated by quantum phase transitions.
Quantum cryptographic system with reduced data loss
Lo, Hoi-Kwong (1309, Low Block, Lei Moon House Ap Lei Chau Estate, Hong Kong, HK); Chau, Hoi Fung (Flat C, 42nd Floor, Tower 1, University Heights 23 Pokfield Road, Pokfulam, Hong Kong, HK)
1998-01-01T23:59:59.000Z
A secure method for distributing a random cryptographic key with reduced data loss. Traditional quantum key distribution systems employ similar probabilities for the different communication modes and thus reject at least half of the transmitted data. The invention substantially reduces the amount of discarded data (those that are encoded and decoded in different communication modes e.g. using different operators) in quantum key distribution without compromising security by using significantly different probabilities for the different communication modes. Data is separated into various sets according to the actual operators used in the encoding and decoding process and the error rate for each set is determined individually. The invention increases the key distribution rate of the BB84 key distribution scheme proposed by Bennett and Brassard in 1984. Using the invention, the key distribution rate increases with the number of quantum signals transmitted and can be doubled asymptotically.
Quantum search algorithms on the hypercube
Birgit Hein; Gregor Tanner
2009-06-17T23:59:59.000Z
We investigate a set of discrete-time quantum search algorithms on the n-dimensional hypercube following a proposal by Shenvi, Kempe and Whaley. We show that there exists a whole class of quantum search algorithms in the symmetry reduced space which perform a search of a marked vertex in time of order $\\sqrt{N}$ where $N = 2^n$, the number of vertices. In analogy to Grover's algorithm, the spatial search is effectively facilitated through a rotation in a two-level sub-space of the full Hilbert space. In the hypercube, these two-level systems are introduced through avoided crossings. We give estimates on the quantum states forming the 2-level sub-spaces at the avoided crossings and derive improved estimates on the search times.
Quantum cryptographic system with reduced data loss
Lo, H.K.; Chau, H.F.
1998-03-24T23:59:59.000Z
A secure method for distributing a random cryptographic key with reduced data loss is disclosed. Traditional quantum key distribution systems employ similar probabilities for the different communication modes and thus reject at least half of the transmitted data. The invention substantially reduces the amount of discarded data (those that are encoded and decoded in different communication modes e.g. using different operators) in quantum key distribution without compromising security by using significantly different probabilities for the different communication modes. Data is separated into various sets according to the actual operators used in the encoding and decoding process and the error rate for each set is determined individually. The invention increases the key distribution rate of the BB84 key distribution scheme proposed by Bennett and Brassard in 1984. Using the invention, the key distribution rate increases with the number of quantum signals transmitted and can be doubled asymptotically. 23 figs.
Generalized multi-photon quantum interference
Max Tillmann; Si-Hui Tan; Sarah E. Stoeckl; Barry C. Sanders; Hubert de Guise; René Heilmann; Stefan Nolte; Alexander Szameit; Philip Walther
2015-02-12T23:59:59.000Z
Non-classical interference of photons lies at the heart of optical quantum information processing. This effect is exploited in universal quantum gates as well as in purpose-built quantum computers that solve the BosonSampling problem. Although non-classical interference is often associated with perfectly indistinguishable photons this only represents the degenerate case, hard to achieve under realistic experimental conditions. Here we exploit tunable distinguishability to reveal the full spectrum of multi-photon non-classical interference. This we investigate in theory and experiment by controlling the delay times of three photons injected into an integrated interferometric network. We derive the entire coincidence landscape and identify transition matrix immanants as ideally suited functions to describe the generalized case of input photons with arbitrary distinguishability. We introduce a compact description by utilizing a natural basis which decouples the input state from the interferometric network, thereby providing a useful tool for even larger photon numbers.
Quantum Phase Transition in a Graphene Model
Simon Hands; Costas Strouthos
2008-08-20T23:59:59.000Z
We present results for the equation of state of a graphene-like model in an effort to understand the properties of its quantum phase transition. The N_f fermion species interact through a three dimensional instantaneous Coulomb potential. Since there are no reliable analytical tools that work for all values of N_f and the coupling constant g, we rely on Monte Carlo simulations to calculate the critical properties of the model near the phase transition. We consider the four-component formulation for the fermion fields, which arises naturally as the continuum limit of the staggered fermion construction in (2+1) dimensions. In the limit of infinitely strong Coulomb interaction, the system undergoes a quantum phase transition at a critical number of fermion species N_fc ~ 4.7. We also calculate the values of the critical exponents at the quantum phase transition.
Experimental realisation of Shor's quantum factoring algorithm using qubit recycling
Enrique Martin-Lopez; Anthony Laing; Thomas Lawson; Roberto Alvarez; Xiao-Qi Zhou; Jeremy L. O'Brien
2012-10-24T23:59:59.000Z
Quantum computational algorithms exploit quantum mechanics to solve problems exponentially faster than the best classical algorithms. Shor's quantum algorithm for fast number factoring is a key example and the prime motivator in the international effort to realise a quantum computer. However, due to the substantial resource requirement, to date, there have been only four small-scale demonstrations. Here we address this resource demand and demonstrate a scalable version of Shor's algorithm in which the n qubit control register is replaced by a single qubit that is recycled n times: the total number of qubits is one third of that required in the standard protocol. Encoding the work register in higher-dimensional states, we implement a two-photon compiled algorithm to factor N=21. The algorithmic output is distinguishable from noise, in contrast to previous demonstrations. These results point to larger-scale implementations of Shor's algorithm by harnessing scalable resource reductions applicable to all physical architectures.
Limited Holism and Real-Vector-Space Quantum Theory
Lucien Hardy; William K. Wootters
2010-05-26T23:59:59.000Z
Quantum theory has the property of "local tomography": the state of any composite system can be reconstructed from the statistics of measurements on the individual components. In this respect the holism of quantum theory is limited. We consider in this paper a class of theories more holistic than quantum theory in that they are constrained only by "bilocal tomography": the state of any composite system is determined by the statistics of measurements on pairs of components. Under a few auxiliary assumptions, we derive certain general features of such theories. In particular, we show how the number of state parameters can depend on the number of perfectly distinguishable states. We also show that real-vector-space quantum theory, while not locally tomographic, is bilocally tomographic.
An Introduction to Quantum Control
James, Matthew
, stochastic control, quantum control, systems biology, networks, etc modern control #12;Quantum Control: Control of physical systems whose behaviour is dominated by the laws of quantum mechanics. 2003: Dowling of Quantum Control: controller quantum system control actions #12;· Closed loop - control actions depend
Topological solitons in the noncommutative plane and quantum Hall Skyrmions
Ezawa, Z.F. [Department of Physics, Tohoku University, Sendai, 980-8578 (Japan); Tsitsishvili, G. [Department of Physics, Tohoku University, Sendai, 980-8578 (Japan); Department of Theoretical Physics, A. Razmadze Mathematical Institute, Tbilisi, 380093 (Georgia)
2005-10-15T23:59:59.000Z
We analyze topological solitons in the noncommutative plane by taking a concrete instance of the quantum Hall system with the SU(N) symmetry, where a soliton is identified with a Skyrmion. It is shown that a topological soliton induces an excitation of the electron number density from the ground-state value around it. When a judicious choice of the topological charge density J{sub 0}(x) is made, it acquires a physical reality as the electron density excitation {delta}{rho}{sup cl}(x) around a topological soliton, {delta}{rho}{sup cl}(x)=-J{sub 0}(x). Hence a noncommutative soliton carries necessarily the electric charge proportional to its topological charge. A field-theoretical state is constructed for a soliton state irrespectively of the Hamiltonian. In general, it involves an infinitely many parameters. They are fixed by minimizing its energy once the Hamiltonian is chosen. We study explicitly the cases where the system is governed by the hard-core interaction and by the noncommutative CP{sup N-1} model, where all these parameters are determined analytically and the soliton excitation energy is obtained.
Stabilising entanglement by quantum jump-based feedback
A. R. R. Carvalho; J. J. Hope
2007-05-24T23:59:59.000Z
We show that direct feedback based on quantum jump detection can be used to generate entangled steady states. We present a strategy that is insensitive to detection inefficiencies and robust against errors in the control Hamiltonian. This feedback procedure is also shown to overcome spontaneous emission effects by stabilising states with high degree of entanglement.
Transition state theory, Siegert eigenstates, and quantum mechanical reaction rates
Miller, William H.
Transition state theory, Siegert eigenstates, and quantum mechanical reaction rates Tamar Seideman variables associated with a transition state (i.e., the saddle point of a potential energy surface), on which a general semiclassical transition state theory is based, are shown to be the semiclassical
On the q-quantum gravity loop algebra
Seth Major
2008-02-19T23:59:59.000Z
A class of deformations of the q-quantum gravity loop algebra is shown to be incompatible with the combinatorics of Temperley-Lieb recoupling theory with deformation parameter at a root of unity. This incompatibility appears to extend to more general deformation parameters.
Quantum vs. Classical Read-once Branching Programs
Martin Sauerhoff
2005-09-23T23:59:59.000Z
The paper presents the first nontrivial upper and lower bounds for (non-oblivious) quantum read-once branching programs. It is shown that the computational power of quantum and classical read-once branching programs is incomparable in the following sense: (i) A simple, explicit boolean function on 2n input bits is presented that is computable by error-free quantum read-once branching programs of size O(n^3), while each classical randomized read-once branching program and each quantum OBDD for this function with bounded two-sided error requires size 2^{\\Omega(n)}. (ii) Quantum branching programs reading each input variable exactly once are shown to require size 2^{\\Omega(n)} for computing the set-disjointness function DISJ_n from communication complexity theory with two-sided error bounded by a constant smaller than 1/2-2\\sqrt{3}/7. This function is trivially computable even by deterministic OBDDs of linear size. The technically most involved part is the proof of the lower bound in (ii). For this, a new model of quantum multi-partition communication protocols is introduced and a suitable extension of the information cost technique of Jain, Radhakrishnan, and Sen (2003) to this model is presented.
Ordinary versus PT-symmetric ?³ quantum field theory
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Bender, Carl M.; Branchina, Vincenzo; Messina, Emanuele
2012-04-01T23:59:59.000Z
A quantum-mechanical theory is PT-symmetric if it is described by a Hamiltonian that commutes with PT, where the operator P performs space reflection and the operator T performs time reversal. A PT-symmetric Hamiltonian often has a parametric region of unbroken PT symmetry in which the energy eigenvalues are all real. There may also be a region of broken PT symmetry in which some of the eigenvalues are complex. These regions are separated by a phase transition that has been repeatedly observed in laboratory experiments. This paper focuses on the properties of a PT-symmetric ig?³ quantum field theory. This quantum field theory is the analog of the PT-symmetric quantum-mechanical theory described by the Hamiltonian H=p²+ix³, whose eigenvalues have been rigorously shown to be all real. This paper compares the renormalization group properties of a conventional Hermitian g?³ quantum field theory with those of the PT-symmetric ig?³ quantum field theory. It is shown that while the conventional g?³ theory in d=6 dimensions is asymptotically free, the ig?³ theory is like a g?? theory in d=4 dimensions; it is energetically stable, perturbatively renormalizable, and trivial.
Scalable Digital Hardware for a Trapped Ion Quantum Computer
Mount, Emily; Vrijsen, Geert; Adams, Michael; Baek, So-Young; Hudek, Kai; Isabella, Louis; Crain, Stephen; van Rynbach, Andre; Maunz, Peter; Kim, Jungsang
2015-01-01T23:59:59.000Z
Many of the challenges of scaling quantum computer hardware lie at the interface between the qubits and the classical control signals used to manipulate them. Modular ion trap quantum computer architectures address scalability by constructing individual quantum processors interconnected via a network of quantum communication channels. Successful operation of such quantum hardware requires a fully programmable classical control system capable of frequency stabilizing the continuous wave lasers necessary for trapping and cooling the ion qubits, stabilizing the optical frequency combs used to drive logic gate operations on the ion qubits, providing a large number of analog voltage sources to drive the trap electrodes, and a scheme for maintaining phase coherence among all the controllers that manipulate the qubits. In this work, we describe scalable solutions to these hardware development challenges.
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AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level: National5Sales for4,645 3,625 1,006 492 742EnergyOn AprilA groupTuba City, Arizona, DisposalFourthN V O 1 8 7 +New York, New
Generalized quantum defect methods in quantum chemistry
Altunata, Serhan
2006-01-01T23:59:59.000Z
The reaction matrix of multichannel quantum defect theory, K, gives a complete picture of the electronic structure and the electron - nuclear dynamics for a molecule. The reaction matrix can be used to examine both bound ...
On the "principle of the quantumness", the quantumness of Relativity,
D'Ariano, Giacomo Mauro
-priority, and that the Lucien Hardy's program on Quantum Gravity should be paralleled by an analogous program on Quantum Field of Quantum Gravity--Lucien Hardy would say. Or, even to a more profound understanding of the whole Physics
Quantum Signatures of Spacetime Graininess Quantum Signatures of Spacetime
Quantum Field Theory on Noncommutative Spacetime Implementing Poincaré Symmetry Hopf Algebras, Drinfel Quantum Mechanics on Noncommutative Spacetime 4 Quantum Field Theory on Noncommutative Spacetime Covariant Derivatives and Field Strength Noncommutative Gauge Theories 6 Signatures of Spin
Brookhaven National Laboratory Number: Revision
Ohta, Shigemi
Brookhaven National Laboratory Number: Revision: PS-ESH-0057 01 Effective: Page 1 of 9 06 Chris Weilandics Signature on file Department ES&H Approval printed name Signature Date Lori Stiegler Signature on file #12;Number: PS-ESH-0057 Revision: 01 Effective: 06/08/12 Page 2 of 9 The only official
Revealing Quantum Advantage in a Quantum Network
Kaushiki Mukherjee; Biswajit Paul; Debasis Sarkar
2014-10-01T23:59:59.000Z
The assumption of source independence was used to reveal nonlocal (apart from standard Bell-CHSH scenario) nature of correlations generated in entanglement swapping experiments. In this work, we have derived a set of sufficient criteria, imposed on the states (produced by the sources) under which source independence can reveal nonbilocal nature of correlations in a quantum network. To show this, we have considered real two qubit X states thereby discussing the various utilities of assuming source independence in a quantum network.
Hohng, Sung Chul
, Renthof 5, D-35032 Marburg, Germany (Received 1 July 1999) Two phase-locked pulses are used to coherently of transform-limited pulses with a pulse duration of 150 fs. We produce two phase-locked collinear pulses excite excitonic polarizations. It is shown that the second pulse can either be strongly amplified
Propagation of vector solitons in a quasi-resonant medium with stark deformation of quantum states
Sazonov, S. V., E-mail: sazonov.sergei@gmail.com [National Research Centre Kurchatov Institute (Russian Federation); Ustinov, N. V., E-mail: n_ustinov@mail.ru [Moscow State Railway University, Kaliningrad Branch (Russian Federation)
2012-11-15T23:59:59.000Z
The nonlinear dynamics of a vector two-component optical pulse propagating in quasi-resonance conditions in a medium of nonsymmetric quantum objects is investigated for Stark splitting of quantum energy levels by an external electric field. We consider the case when the ordinary component of the optical pulse induces {sigma} transitions, while the extraordinary component induces the {pi} transition and shifts the frequencies of the allowed transitions due to the dynamic Stark effect. It is found that under Zakharov-Benney resonance conditions, the propagation of the optical pulse is accompanied by generation of an electromagnetic pulse in the terahertz band and is described by the vector generalization of the nonlinear Yajima-Oikawa system. It is shown that this system (as well as its formal generalization with an arbitrary number of optical components) is integrable by the inverse scattering transformation method. The corresponding Darboux transformations are found for obtaining multisoliton solutions. The influence of transverse effects on the propagation of vector solitons is investigated. The conditions under which transverse dynamics leads to self-focusing (defocusing) of solitons are determined.
Zeynab Harsij; Behrouz Mirza
2014-09-24T23:59:59.000Z
A helicity entangled tripartite state is considered in which the degree of entanglement is preserved in non-inertial frames. It is shown that Quantum Entanglement remains observer independent. As another measure of quantum correlation, Quantum Discord has been investigated. It is explicitly shown that acceleration has no effect on the degree of quantum correlation for the bipartite and tripartite helicity entangled states. Geometric Quantum Discord as a Hilbert-Schmidt distance is computed for helicity entangled states. It is shown that living in non-inertial frames does not make any influence on this distance, either. In addition, the analysis has been extended beyond single mode approximation to show that acceleration does not have any impact on the quantum features in the limit beyond the single mode. As an interesting result, while the density matrix depends on the right and left Unruh modes, the Negativity as a measure of Quantum Entanglement remains constant. Also, Quantum Discord does not change beyond single mode approximation.
Utah, University of
to monitor this time evolution using the measurement results. This effect is shown to be equivalent the statistics of the results of a series of measurements performed on a single system, with no time evolution of measurements are independent of the measurement results. Therefore it was also suggested that the quantum Zeno
Quantum dynamics and macroscopic quantum tunneling of two weakly coupled condensates
René John Kerkdyk; S. Sinha
2012-09-24T23:59:59.000Z
We study the quantum dynamics of a Bose Josephson junction(BJJ) made up of two coupled Bose-Einstein condensates. Apart from the usual ac Josephson oscillations, two different dynamical states of BJJ can be observed by tuning the inter-particle interaction strength, which are known as '$\\pi$-oscillation' with relative phase $\\pi$ between the condensates and 'macroscopic self-trapped' (MST) state with finite number imbalance. By choosing appropiate intial state we study above dynamical branches quantum mechanically and compare with classical dynamics. The stability region of the '$\\pi$-oscillation' is separated from that of 'MST' state at a critical coupling strength. Also a significant change in the energy spectrum takes place above the critical coupling strength, and pairs of (quasi)-degenerate excited states appear. The original model of BJJ can be mapped on to a simple Hamiltonian describing quantum particle in an 'effective potential' with an effective Planck constant. Different dynamical states and degenerate excited states in the energy spectrum can be understood in this 'effective potential' approach. Also possible novel quantum phenomena like 'macroscopic quantum tunneling'(MQT) become evident from the simple picture of 'effective potential'. We study decay of metastable '$\\pi$-oscillation' by MQT through potential barrier. The doubly degenerate excited states in the energy spectrum are associated with the classically degenerate MST states with equal and opposite number imbalance. We calculate the energy splitting between these quasi-degenerate excited states due to MQT of the condensate between classically degenerate MST states.
Classical and quantum Big Brake cosmology for scalar field and tachyonic models
Kamenshchik, A. Yu. [Dipartimento di Fisica e Astronomia and INFN, Via Irnerio 46, 40126 Bologna (Italy) and L.D. Landau Institute for Theoretical Physics of the Russian Academy of Sciences, Kosygin str. 2, 119334 Moscow (Russian Federation); Manti, S. [Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy)
2013-02-21T23:59:59.000Z
We study a relation between the cosmological singularities in classical and quantum theory, comparing the classical and quantum dynamics in some models possessing the Big Brake singularity - the model based on a scalar field and two models based on a tachyon-pseudo-tachyon field . It is shown that the effect of quantum avoidance is absent for the soft singularities of the Big Brake type while it is present for the Big Bang and Big Crunch singularities. Thus, there is some kind of a classical - quantum correspondence, because soft singularities are traversable in classical cosmology, while the strong Big Bang and Big Crunch singularities are not traversable.
Models of quantum computation and quantum programming languages
J. A. Miszczak
2011-12-03T23:59:59.000Z
The goal of the presented paper is to provide an introduction to the basic computational models used in quantum information theory. We review various models of quantum Turing machine, quantum circuits and quantum random access machine (QRAM) along with their classical counterparts. We also provide an introduction to quantum programming languages, which are developed using the QRAM model. We review the syntax of several existing quantum programming languages and discuss their features and limitations.
Current commutator anomalies in finite-element quantum electrodynamics
Dean F. Miller
1993-12-20T23:59:59.000Z
Four-dimensional quantum electrodynamics has been formulated on a hypercubic Minkowski finite-element lattice. The equations of motion have been derived so as to preserve lattice gauge invariance and have been shown to be unitary. In addition, species doubling is avoided due to the nonlocality of the interactions. The model is used to investigate the lattice current algebra. Regularization of the current is shown to arise in a natural and nonarbitrary way. The commutators of the lattice current are calculated and shown to have the expected qualitative behavior. These lattice results are compared to various continuum calculations. (Five figures available from author.)
Jeremy L. O'Brien; Akira Furusawa; Jelena Vu?kovi?
2010-03-20T23:59:59.000Z
The first quantum technology, which harnesses uniquely quantum mechanical effects for its core operation, has arrived in the form of commercially available quantum key distribution systems that achieve enhanced security by encoding information in photons such that information gained by an eavesdropper can be detected. Anticipated future quantum technologies include large-scale secure networks, enhanced measurement and lithography, and quantum information processors, promising exponentially greater computation power for particular tasks. Photonics is destined for a central role in such technologies owing to the need for high-speed transmission and the outstanding low-noise properties of photons. These technologies may use single photons or quantum states of bright laser beams, or both, and will undoubtably apply and drive state-of-the-art developments in photonics.
Generalized quantum secret sharing
Singh, Sudhir Kumar; Srikanth, R. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Optics Group, Raman Research Institute, Bangalore-560080 (India)
2005-01-01T23:59:59.000Z
We explore a generalization of quantum secret sharing (QSS) in which classical shares play a complementary role to quantum shares, exploring further consequences of an idea first studied by Nascimento, Mueller-Quade, and Imai [Phys. Rev. A 64, 042311 (2001)]. We examine three ways, termed inflation, compression, and twin thresholding, by which the proportion of classical shares can be augmented. This has the important application that it reduces quantum (information processing) players by replacing them with their classical counterparts, thereby making quantum secret sharing considerably easier and less expensive to implement in a practical setting. In compression, a QSS scheme is turned into an equivalent scheme with fewer quantum players, compensated for by suitable classical shares. In inflation, a QSS scheme is enlarged by adding only classical shares and players. In a twin-threshold scheme, we invoke two separate thresholds for classical and quantum shares based on the idea of information dilution.
Chitra Shukla; Anirban Pathak; R. Srikanth
2012-10-09T23:59:59.000Z
It is shown that maximally efficient protocols for secure direct quantum communications can be constructed using any arbitrary orthogonal basis. This establishes that no set of quantum states (e.g. GHZ states, W states, Brown states or Cluster states) has an advantage over the others, barring the relative difficulty in physical implementation. The work provides a wide choice of states for experimental realization of direct secure quantum communication protocols. We have also shown that this protocol can be generalized to a completely orthogonal state based protocol of Goldenberg-Vaidman (GV) type. The security of these protocols essentially arises from duality and monogamy of entanglement. This stands in contrast to protocols that employ non-orthogonal states, like Bennett-Brassard 1984 (BB84), where the security essentially comes from non-commutativity in the observable algebra.
Wave-Packet Revivals for Quantum Systems with Nondegenerate Energies
Robert Bluhm; Alan Kostelecky; Bogdan Tudose
1996-09-26T23:59:59.000Z
The revival structure of wave packets is examined for quantum systems having energies that depend on two nondegenerate quantum numbers. For such systems, the evolution of the wave packet is controlled by two classical periods and three revival times. These wave packets exhibit quantum beats in the initial motion as well as new types of long-term revivals. The issue of whether fractional revivals can form is addressed. We present an analytical proof showing that at certain times equal to rational fractions of the revival times the wave packet can reform as a sum of subsidiary waves and that both conventional and new types of fractional revivals can occur.
Limiting the complexity of quantum states: a toy theory
Valerio Scarani
2015-03-30T23:59:59.000Z
This paper discusses a restriction of quantum theory, in which very complex states would be excluded. The toy theory is phrased in the language of the circuit model for quantum computing, its key ingredient being a limitation on the number of interactions that \\textit{each} qubit may undergo. As long as one stays in the circuit model, the toy theory is consistent and may even match what we shall be ever able to do in a controlled laboratory experiment. The direct extension of the restriction beyond the circuit model conflicts with observed facts: the possibility of restricting the complexity of quantum state, while saving phenomena, remains an open question.
Quantum effects in electron beam pumped GaAs
Yahia, M. E. [Faculty of Engineering, The British University in Egypt (BUE), El-Shorouk City, Cairo (Egypt) [Faculty of Engineering, The British University in Egypt (BUE), El-Shorouk City, Cairo (Egypt); National Institute of Laser Enhanced Sciences (NILES), Cairo University (Egypt); Azzouz, I. M. [National Institute of Laser Enhanced Sciences (NILES), Cairo University (Egypt)] [National Institute of Laser Enhanced Sciences (NILES), Cairo University (Egypt); Moslem, W. M. [Department of Physics, Faculty of Science, Port Said University, Port Said (Egypt)] [Department of Physics, Faculty of Science, Port Said University, Port Said (Egypt)
2013-08-19T23:59:59.000Z
Propagation of waves in nano-sized GaAs semiconductor induced by electron beam are investigated. A dispersion relation is derived by using quantum hydrodynamics equations including the electrons and holes quantum recoil effects, exchange-correlation potentials, and degenerate pressures. It is found that the propagating modes are instable and strongly depend on the electron beam parameters, as well as the quantum recoil effects and degenerate pressures. The instability region shrinks with the increase of the semiconductor number density. The instability arises because of the energetic electron beam produces electron-hole pairs, which do not keep in phase with the electrostatic potential arising from the pair plasma.
Quantum Process Tomography via L1-norm Minimization
Robert L. Kosut
2009-03-05T23:59:59.000Z
For an initially well designed but imperfect quantum information system, the process matrix is almost sparse in an appropriate basis. Existing theory and associated computational methods (L1-norm minimization) for reconstructing sparse signals establish conditions under which the sparse signal can be perfectly reconstructed from a very limited number of measurements (resources). Although a direct extension to quantum process tomography of the L1-norm minimization theory has not yet emerged, the numerical examples presented here, which apply L1-norm minimization to quantum process tomography, show a significant reduction in resources to achieve a desired estimation accuracy over existing methods.
INSTITUTE for QUANTUM STRUCTURES AND DEVICES
Plotkin, Steven S.
, and #12;the design and fabrication of quantum devices based on magnetic, quantum dot, and superconducting
Open Systems Dynamics for Propagating Quantum Fields
Ben Q. Baragiola
2014-08-18T23:59:59.000Z
In this dissertation, I explore interactions between matter and propagating light. The electromagnetic field is modeled as a reservoir of quantum harmonic oscillators successively streaming past a quantum system. Each weak and fleeting interaction entangles the light and the system, and the light continues its course. Within the framework of open quantum systems, the light is eventually traced out, leaving the reduced quantum state of the system as the primary mathematical subject. Two major results are presented. The first is a master equation approach for a quantum system interacting with a traveling wave packet prepared with a definite number of photons. In contrast to quasi-classical states, such as coherent or thermal fields, these N-photon states possess temporal mode entanglement, and local interactions in time have nonlocal consequences. The second is a model for a three-dimensional light-matter interface for an atomic ensemble interacting with a paraxial laser beam and its application to the generation of QND spin squeezing. Both coherent and incoherent dynamics due to spatially inhomogeneous atom-light coupling across the ensemble are accounted for. Measurement of paraxially scattered light can generate squeezing of an atomic spin wave, while diffusely scattered photons lead to spatially local decoherence.
Black Holes with Flavors of Quantum Hair?
Gia Dvali
2006-07-20T23:59:59.000Z
We show that black holes can posses a long-range quantum hair of super-massive tensor fields, which can be detected by Aharonov-Bohm tabletop interference experiments, in which a quantum-hairy black hole, or a remnant particle, passes through the loop of a magnetic solenoid. The long distance effect does not decouple for an arbitrarily high mass of the hair-providing field. Because Kaluza-Klein and String theories contain infinite number of massive tensor fields, we study black holes with quantum Kaluza-Klein hair. We show that in five dimensions such a black hole can be interpreted as a string of `combed' generalized magnetic monopoles, with their fluxes confined along it. For the compactification on a translation-invariant circle, this substructure uncovers hidden flux conservation and quantization of the monopole charges, which constrain the quantum hair of the resulting four-dimensional black hole. For the spin-2 quantum hair this result is somewhat unexpected, since the constituent `magnetic' charges have no `electric' counterparts. Nevertheless, the information about their quantization is encoded in singularity.
S. Denisov; S. Kohler; P. Hanggi
2009-02-24T23:59:59.000Z
We investigate the quantum ratchet effect under the influence of weak dissipation which we treat within a Floquet-Markov master equation approach. A ratchet current emerges when all relevant symmetries are violated. Using time-reversal symmetric driving we predict a purely dissipation-induced quantum ratchet current. This directed quantum transport results from bath-induced superpositions of non-transporting Floquet states.
Quantum dense key distribution
Degiovanni, I.P.; Ruo Berchera, I.; Castelletto, S.; Rastello, M.L.; Bovino, F.A.; Colla, A.M.; Castagnoli, G. [Istituto Elettrotecnico Nazionale G. Ferraris, Strada delle Cacce 91, 10135 Torino (Italy); ELSAG SpA, Via Puccini 2, 16154, Genova (Italy)
2004-03-01T23:59:59.000Z
This paper proposes a protocol for quantum dense key distribution. This protocol embeds the benefits of a quantum dense coding and a quantum key distribution and is able to generate shared secret keys four times more efficiently than the Bennet-Brassard 1984 protocol. We hereinafter prove the security of this scheme against individual eavesdropping attacks, and we present preliminary experimental results, showing its feasibility.
Quantum information science as an approach to complex quantum systems
Michael A. Nielsen
2002-08-13T23:59:59.000Z
What makes quantum information science a science? These notes explore the idea that quantum information science may offer a powerful approach to the study of complex quantum systems. We discuss how to quantify complexity in quantum systems, and argue that there are two qualitatively different types of complex quantum system. We also explore ways of understanding complex quantum dynamics by quantifying the strength of a quantum dynamical operation as a physical resource. This is the text for a talk at the ``Sixth International Conference on Quantum Communication, Measurement and Computing'', held at MIT, July 2002. Viewgraphs for the talk may be found at http://www.qinfo.org/talks/.
Reconstruction theorem for quantum stochastic processes
V. P. Belavkin
2005-12-17T23:59:59.000Z
Statistically interpretable axioms are formulated that define a quantum stochastic process (QSP) as a causally ordered operator field in an arbitrary space-time region T of an open quantum system under a sequential observation at a discrete space-time localization. It is shown that to every QSP described in the weak sense by a self-consistent system of causally ordered correlation kernels there corresponds a unique, up to unitary equivalence, minimal QSP in the strong sense. It is shown that the proposed QSP construction, which reduces in the case of the linearly ordered discrete T=Z to the construction of the inductive limit of Lindblad's canonical representations, corresponds to Kolmogorov's classical reconstruction if the order on T is ignored and leads to Lewis construction if one uses the system of all (not only causal) correlation kernels, regarding this system as lexicographically preordered on T. The approach presented encompasses both nonrelativistic and relativistic irreversible dynamics of open quantum systems and fields satisfying the conditions of local commutativity and semigroup covariance. Also given are necessary and sufficient conditions of dynamicity (or conditional Markovianity) and regularity, these leading to the properties of complete mixing (relaxation) and ergodicity of the QSP.
FOURIER TRANSFORM MULTIPLE QUANTUM NMR
Drobny, G.
2011-01-01T23:59:59.000Z
of transition observed in Fourier transform multiple quantumDecember 18-19, 1979 FOURIER TRANSFORM MULTIPLE QUANTUM NMRof London, December 1978. FOURIER TRANSFO~~ MULTIPLE QUANTUM
Vacuum Energy in Quantum Graphs
Wilson, Justin
2007-07-14T23:59:59.000Z
We calculate the vacuum energy in quantum graphs. Vacuum energy arose in quantum physics but has an independent mathematical interest as a functional carrying information about the eigenvalue spectrum of a system. A quantum graph is a metric graph...
Generalizations of quantum statistics
O. W. Greenberg
2008-05-02T23:59:59.000Z
We review generalizations of quantum statistics, including parabose, parafermi, and quon statistics, but not including anyon statistics, which is special to two dimensions.
Rongkuo Zhao; Alejandro Manjavacas; F. Javier García de Abajo; J. B. Pendry
2012-09-25T23:59:59.000Z
We investigate the frictional forces due to quantum fluctuations acting on a small sphere rotating near a surface. At zero temperature, we find the frictional force near a surface to be several orders of magnitude larger than that for the sphere rotating in vacuum. For metallic materials with typical conductivity, quantum friction is maximized by matching the frequency of rotation with the conductivity. Materials with poor conductivity are favored to obtain large quantum frictions. For semiconductor materials that are able to support surface plasmon polaritons, quantum friction can be further enhanced by several orders of magnitude due to the excitation of surface plasmon polaritons.
QUANTUM CONVERSION IN PHOTOSYNTHESIS
Calvin, Melvin
2008-01-01T23:59:59.000Z
QUANTUM CONVERSION IN PHOTOSYNTHESIS Melvin Calvin Januaryas it occurs in modern photosynthesis can only take place inof the problem or photosynthesis, or any specific aspect of
Multiparty quantum secret sharing
Zhang Zhanjun [School of Physics and Material Science, Anhui University, Hefei 230039 (China); Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China); Li Yong [Department of Physics, Huazhong Normal University, Wuhan 430079 (China); Man Zhongxiao [Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China)
2005-04-01T23:59:59.000Z
Based on a quantum secure direct communication (QSDC) protocol [Phys. Rev. A 69 052319 (2004)], we propose a (n,n)-threshold scheme of multiparty quantum secret sharing of classical messages (QSSCM) using only single photons. We take advantage of this multiparty QSSCM scheme to establish a scheme of multiparty secret sharing of quantum information (SSQI), in which only all quantum information receivers collaborate can the original qubit be reconstructed. A general idea is also proposed for constructing multiparty SSQI schemes from any QSSCM scheme.
Ekert, A K; Hayden, P; Inamori, H; Jones, J A; Oi, D K L; Vedral, V
2000-01-01T23:59:59.000Z
We describe in detail a general strategy for implementing a conditional geometric phase between two spins. Combined with single-spin operations, this simple operation is a universal gate for quantum computation, in that any unitary transformation can be implemented with arbitrary precision using only single-spin operations and conditional phase shifts. Thus quantum geometrical phases can form the basis of any quantum computation. Moreover, as the induced conditional phase depends only on the geometry of the paths executed by the spins it is resilient to certain types of errors and offers the potential of a naturally fault-tolerant way of performing quantum computation.
A. Ekert; M. Ericsson; P. Hayden; H. Inamori; J. A. Jones; D. K. L. Oi; V. Vedral
2000-04-04T23:59:59.000Z
We describe in detail a general strategy for implementing a conditional geometric phase between two spins. Combined with single-spin operations, this simple operation is a universal gate for quantum computation, in that any unitary transformation can be implemented with arbitrary precision using only single-spin operations and conditional phase shifts. Thus quantum geometrical phases can form the basis of any quantum computation. Moreover, as the induced conditional phase depends only on the geometry of the paths executed by the spins it is resilient to certain types of errors and offers the potential of a naturally fault-tolerant way of performing quantum computation.
Vukmirovic, Nenad
2010-01-01T23:59:59.000Z
Petersilka, Density Functional Theory (Springer, New York,Quantum Dots: Theory Nenad Vukmirovi´ and Lin-Wang Wang cdensity functional theory; electronic structure; empirical
Reverse quantum state engineering using electronic feedback loops
Gerold Kiesslich; Clive Emary; Gernot Schaller; Tobias Brandes
2012-11-30T23:59:59.000Z
We propose an all-electronic technique to manipulate and control interacting quantum systems by unitary single-jump feedback conditioned on the outcome of a capacitively coupled electrometer and in particular a single-electron transistor. We provide a general scheme to stabilize pure states in the quantum system and employ an effective Hamiltonian method for the quantum master equation to elaborate on the nature of stabilizable states and the conditions under which state purification can be achieved. The state engineering within the quantum feedback scheme is shown to be linked with the solution of an inverse eigenvalue problem. Two applications of the feedback scheme are presented in detail: (i) stabilization of delocalized pure states in a single charge qubit and (ii) entanglement stabilization in two coupled charge qubits. In the latter example we demonstrate the stabilization of a maximally entangled Bell state for certain detector positions and local feedback operations.
Quantum-enhanced deliberation of learning agents using trapped ions
Vedran Dunjko; Nicolai Friis; Hans J. Briegel
2015-01-31T23:59:59.000Z
A scheme that successfully employs quantum mechanics in the design of autonomous learning agents has recently been reported in the context of the projective simulation (PS) model for artificial intelligence. In that approach, the key feature of a PS agent, a specific type of memory which is explored via random walks, was shown to be amenable to quantization. In particular, classical random walks were substituted by Szegedy-type quantum walks, allowing for a speed-up. In this work we propose how such classical and quantum agents can be implemented in systems of trapped ions. We employ a generic construction by which the classical agents are `upgraded' to their quantum counterparts by nested coherent controlization, and we outline how this construction can be realized in ion traps. Our results provide a flexible modular architecture for the design of PS agents. Furthermore, we present numerical simulations of simple PS agents which analyze the robustness of our proposal under certain noise models.
Real-world Quantum Sensors: Evaluating Resources for Precision Measurement
Nicholas Thomas-Peter; Brian J Smith; Animesh Datta; Lijian Zhang; Uwe Dorner; Ian A Walmsley
2011-05-19T23:59:59.000Z
Quantum physics holds the promise of enabling certain tasks with better performance than possible when only classical resources are employed. The quantum phenomena present in many experiments signify nonclassical behavior, but do not always imply superior performance. Quantifying the enhancement achieved from quantum behavior requires careful analysis of the resources involved. We analyze the specific case of parameter estimation using an optical interferometer, where increased precision can be achieved using quantum probe states. Common performance measures are examined and it is shown that some overestimate the improvement. For the simplest experimental case we compare the different measures and show this overestimate explicitly. We give the preferred analysis of real-world experiments and calculate benchmark values for experimental parameters necessary to realize a precision enhancement.
Why Do the Quantum Observables Form a Jordan Operator Algebra?
Gerd Niestegge
2010-01-21T23:59:59.000Z
The Jordan algebra structure of the bounded real quantum observables was recognized already in the early days of quantum mechanics. While there are plausible reasons for most parts of this structure, the existence of the distributive nonassociative multiplication operation is hard to justify from a physical or statistical point of view. Considering the non-Boolean extension of classical probabilities, presented in a recent paper, it is shown in this paper that such a multiplication operation can be derived from certain properties of the conditional probabilities and the observables, i.e., from postulates with a clear statistical interpretation. The well-known close relation between Jordan operator algebras and C*-algebras then provides the connection to the quantum-mechanical Hilbert space formalism, thus resulting in a novel axiomatic approach to general quantum mechanics that includes the types II and III von Neumann algebras.
Quantum dot conjugates in a sub-micrometer fluidic channel
Stavis, Samuel M.; Edel, Joshua B.; Samiee, Kevan T.; Craighead, Harold G.
2010-04-13T23:59:59.000Z
A nanofluidic channel fabricated in fused silica with an approximately 500 nm square cross section was used to isolate, detect and identify individual quantum dot conjugates. The channel enables the rapid detection of every fluorescent entity in solution. A laser of selected wavelength was used to excite multiple species of quantum dots and organic molecules, and the emission spectra were resolved without significant signal rejection. Quantum dots were then conjugated with organic molecules and detected to demonstrate efficient multicolor detection. PCH was used to analyze coincident detection and to characterize the degree of binding. The use of a small fluidic channel to detect quantum dots as fluorescent labels was shown to be an efficient technique for multiplexed single molecule studies. Detection of single molecule binding events has a variety of applications including high throughput immunoassays.
Gordon, Ariel; Wang, Christine Y.; Diehl, L.; Kaertner, F. X.; Belyanin, Alexey; Bour, D.; Corzine, S.; Hoefler, G.; Liu, H. C.; Schneider, H.; Maier, T.; Troccoli, M.; Faist, J.; Capasso, Federico
2008-01-01T23:59:59.000Z
A theoretical and experimental study of multimode operation regimes in quantum cascade lasers (QCLs) is presented. It is shown that the fast gain recovery of QCLs promotes two multimode regimes: One is spatial hole burning (SHB) and the other one...
Fast quantum algorithm for numerical gradient estimation
Stephen P. Jordan
2005-01-02T23:59:59.000Z
Given a blackbox for f, a smooth real scalar function of d real variables, one wants to estimate the gradient of f at a given point with n bits of precision. On a classical computer this requires a minimum of d+1 blackbox queries, whereas on a quantum computer it requires only one query regardless of d. The number of bits of precision to which f must be evaluated matches the classical requirement in the limit of large n.
Some foundational aspects of quantum computers and quantum robots.
Benioff, P.; Physics
1998-01-01T23:59:59.000Z
This paper addresses foundational issues related to quantum computing. The need for a universally valid theory such as quantum mechanics to describe to some extent its own validation is noted. This includes quantum mechanical descriptions of systems that do theoretical calculations (i.e. quantum computers) and systems that perform experiments. Quantum robots interacting with an environment are a small first step in this direction. Quantum robots are described here as mobile quantum systems with on-board quantum computers that interact with environments. Included are discussions on the carrying out of tasks and the division of tasks into computation and action phases. Specific models based on quantum Turing machines are described. Differences and similarities between quantum robots plus environments and quantum computers are discussed.
Fibred Coalgebraic Logic and Quantum Protocols
Daniel Marsden
2014-12-30T23:59:59.000Z
Motivated by applications in modelling quantum systems using coalgebraic techniques, we introduce a fibred coalgebraic logic. Our approach extends the conventional predicate lifting semantics with additional modalities relating conditions on different fibres. As this fibred setting will typically involve multiple signature functors, the logic incorporates a calculus of modalities enabling the construction of new modalities using various composition operations. We extend the semantics of coalgebraic logic to this setting, and prove that this extension respects behavioural equivalence. We show how properties of the semantics of modalities are preserved under composition operations, and then apply the calculational aspect of our logic to produce an expressive set of modalities for reasoning about quantum systems, building these modalities up from simpler components. We then demonstrate how these modalities can describe some standard quantum protocols. The novel features of our logic are shown to allow for a uniform description of unitary evolution, and support local reasoning such as "Alice's qubit satisfies condition" as is common when discussing quantum protocols.
Scattering Theory for Open Quantum Systems
J. Behrndt; M. M. Malamud; H. Neidhardt
2006-10-31T23:59:59.000Z
Quantum systems which interact with their environment are often modeled by maximal dissipative operators or so-called Pseudo-Hamiltonians. In this paper the scattering theory for such open systems is considered. First it is assumed that a single maximal dissipative operator $A_D$ in a Hilbert space $\\sH$ is used to describe an open quantum system. In this case the minimal self-adjoint dilation $\\widetilde K$ of $A_D$ can be regarded as the Hamiltonian of a closed system which contains the open system $\\{A_D,\\sH\\}$, but since $\\widetilde K$ is necessarily not semibounded from below, this model is difficult to interpret from a physical point of view. In the second part of the paper an open quantum system is modeled with a family $\\{A(\\mu)\\}$ of maximal dissipative operators depending on energy $\\mu$, and it is shown that the open system can be embedded into a closed system where the Hamiltonian is semibounded. Surprisingly it turns out that the corresponding scattering matrix can be completely recovered from scattering matrices of single Pseudo-Hamiltonians as in the first part of the paper. The general results are applied to a class of Sturm-Liouville operators arising in dissipative and quantum transmitting Schr\\"{o}dinger-Poisson systems.
The distribution of prime numbers on the square root spiral
Harry K. Hahn; Robert Sachs
2008-01-09T23:59:59.000Z
Prime Numbers clearly accumulate on defined spiral graphs,which run through the Square Root Spiral. These spiral graphs can be assigned to different spiral-systems, in which all spiral-graphs have the same direction of rotation and the same -second difference- between the numbers, which lie on these spiral-graphs. A mathematical analysis shows, that these spiral graphs are caused exclusively by quadratic polynomials. For example the well known Euler Polynomial x2+x+41 appears on the Square Root Spiral in the form of three spiral-graphs, which are defined by three different quadratic polynomials. All natural numbers,divisible by a certain prime factor, also lie on defined spiral graphs on the Square Root Spiral (or Spiral of Theodorus, or Wurzelspirale). And the Square Numbers 4, 9, 16, 25, 36 even form a highly three-symmetrical system of three spiral graphs, which divides the square root spiral into three equal areas. Fibonacci number sequences also play a part in the structure of the Square Root Spiral. With the help of the Number-Spiral, described by Mr. Robert Sachs, a comparison can be drawn between the Square Root Spiral and the Ulam Spiral. The shown sections of his study of the number spiral contain diagrams, which are related to my analysis results, especially in regards to the distribution of prime numbers.
Departmental Business Instrument Numbering System
Broader source: Directives, Delegations, and Requirements [Office of Management (MA)]
2000-12-05T23:59:59.000Z
To prescribe procedures for assigning identifying numbers to all Department of Energy (DOE), including the National Nuclear Security Administration, business instruments. Cancels DOE 1331.2B. Canceled by DOE O 540.1A.
Departmental Business Instrument Numbering System
Broader source: Directives, Delegations, and Requirements [Office of Management (MA)]
2005-01-27T23:59:59.000Z
The Order prescribes the procedures for assigning identifying numbers to all Department of Energy (DOE) and National Nuclear Security Administration (NNSA) business instruments. Cancels DOE O 540.1. Canceled by DOE O 540.1B.
Origin of complex quantum amplitudes and Feynman's rules
Goyal, Philip; Knuth, Kevin H.; Skilling, John [Perimeter Institute, Waterloo (Canada); University at Albany (SUNY), New York (United States); Maximum Entropy Data Consultants Ltd., Kenmare (Ireland)
2010-02-15T23:59:59.000Z
Complex numbers are an intrinsic part of the mathematical formalism of quantum theory and are perhaps its most characteristic feature. In this article, we show that the complex nature of the quantum formalism can be derived directly from the assumption that a pair of real numbers is associated with each sequence of measurement outcomes, with the probability of this sequence being a real-valued function of this number pair. By making use of elementary symmetry conditions, and without assuming that these real number pairs have any other algebraic structure, we show that these pairs must be manipulated according to the rules of complex arithmetic. We demonstrate that these complex numbers combine according to Feynman's sum and product rules, with the modulus-squared yielding the probability of a sequence of outcomes.
Quantum Heat Engines, the Second Law and Maxwell's Daemon
Tien D. Kieu
2005-08-22T23:59:59.000Z
We introduce a class of quantum heat engines which consists of two-energy-eigenstate systems, the simplest of quantum mechanical systems, undergoing quantum adiabatic processes and energy exchanges with heat baths, respectively, at different stages of a cycle. Armed with this class of heat engines and some interpretation of heat transferred and work performed at the quantum level, we are able to clarify some important aspects of the second law of thermodynamics. In particular, it is not sufficient to have the heat source hotter than the sink, but there must be a minimum temperature difference between the hotter source and the cooler sink before any work can be extracted through the engines. The size of this minimum temperature difference is dictated by that of the energy gaps of the quantum engines involved. Our new quantum heat engines also offer a practical way, as an alternative to Szilard's engine, to physically realise Maxwell's daemon. Inspired and motivated by the Rabi oscillations, we further introduce some modifications to the quantum heat engines with single-mode cavities in order to, while respecting the second law, extract more work from the heat baths than is otherwise possible in thermal equilibria. Some of the results above are also generalisable to quantum heat engines of an infinite number of energy levels including 1-D simple harmonic oscillators and 1-D infinite square wells.
Full counting statistics as a probe of quantum coherence in a side-coupled double quantum dot system
Xue, Hai-Bin, E-mail: xuehaibin@tyut.edu.cn
2013-12-15T23:59:59.000Z
We study theoretically the full counting statistics of electron transport through side-coupled double quantum dot (QD) based on an efficient particle-number-resolved master equation. It is demonstrated that the high-order cumulants of transport current are more sensitive to the quantum coherence than the average current, which can be used to probe the quantum coherence of the considered double QD system. Especially, quantum coherence plays a crucial role in determining whether the super-Poissonian noise occurs in the weak inter-dot hopping coupling regime depending on the corresponding QD-lead coupling, and the corresponding values of super-Poissonian noise can be relatively enhanced when considering the spins of conduction electrons. Moreover, this super-Poissonian noise bias range depends on the singly-occupied eigenstates of the system, which thus suggests a tunable super-Poissonian noise device. The occurrence-mechanism of super-Poissonian noise can be understood in terms of the interplay of quantum coherence and effective competition between fast-and-slow transport channels. -- Highlights: •The FCS can be used to probe the quantum coherence of side-coupled double QD system. •Probing quantum coherence using FCS may permit experimental tests in the near future. •The current noise characteristics depend on the quantum coherence of this QD system. •The super-Poissonian noise can be enhanced when considering conduction electron spin. •The side-coupled double QD system suggests a tunable super-Poissonian noise device.
Lee, Sang-Bong
1993-09-01T23:59:59.000Z
Quantum manifestation of classical chaos has been one of the extensively studied subjects for more than a decade. Yet clear understanding of its nature still remains to be an open question partly due to the lack of a canonical definition of quantum chaos. The classical definition seems to be unsuitable in quantum mechanics partly because of the Heisenberg quantum uncertainty. In this regard, quantum chaos is somewhat misleading and needs to be clarified at the very fundamental level of physics. Since it is well known that quantum mechanics is more fundamental than classical mechanics, the quantum description of classically chaotic nature should be attainable in the limit of large quantum numbers. The focus of my research, therefore, lies on the correspondence principle for classically chaotic systems. The chaotic damped driven pendulum is mainly studied numerically using the split operator method that solves the time-dependent Schroedinger equation. For classically dissipative chaotic systems in which (multi)fractal strange attractors often emerge, several quantum dissipative mechanisms are also considered. For instance, Hoover`s and Kubo-Fox-Keizer`s approaches are studied with some computational analyses. But the notion of complex energy with non-Hermiticity is extensively applied. Moreover, the Wigner and Husimi distribution functions are examined with an equivalent classical distribution in phase-space, and dynamical properties of the wave packet in configuration and momentum spaces are also explored. The results indicate that quantum dynamics embraces classical dynamics although the classicalquantum correspondence fails to be observed in the classically chaotic regime. Even in the semi-classical limits, classically chaotic phenomena would eventually be suppressed by the quantum uncertainty.
Engineering integrated photonics for heralded quantum gates
T. Meany; D. N. Biggerstaff; M. A. Broome; A. Fedrizzi; M. Delanty; A. Gilchrist; G. D. Marshall; M. J. Steel; A. G. White; M. J. Withford
2015-02-11T23:59:59.000Z
Scaling up linear-optics quantum computing will require multi-photon gates which are compact, phase-stable, exhibit excellent quantum interference, and have success heralded by the detection of ancillary photons. We investigate implementation of the optimal known gate design which meets these requirements: the Knill controlled-Z gate, implemented in integrated laser-written waveguide arrays. We show that device performance is more sensitive to the small deviations in the coupler reflectivity, arising due to the tolerance values of the fabrication method, than phase variations in the circuit. The mode fidelity was also shown to be less sensitive to reflectivity and phase errors than process fidelity. Our best device achieves a fidelity of 0.931+/-0.001 with the ideal 4x4 unitary circuit and a process fidelity of 0.680+/-0.005 with the ideal computational-basis process.
Thermodynamics of N-dimensional quantum walks
Alejandro Romanelli; Raul Donangelo; Renato Portugal; Franklin L. Marquezino
2014-08-22T23:59:59.000Z
The entanglement between the position and coin state of a $N$-dimensional quantum walker is shown to lead to a thermodynamic theory. The entropy, in this thermodynamics, is associated to the reduced density operator for the evolution of chirality, taking a partial trace over positions. From the asymptotic reduced density matrix it is possible to define thermodynamic quantities, such as the asymptotic entanglement entropy, temperature, Helmholz free energy, etc. We study in detail the case of a $2$-dimensional quantum walk, in the case of two different initial conditions: a non-separable coin-position initial state, and a separable one. The resulting entanglement temperature is presented as function of the parameters of the system and those of the initial conditions.
Comment on 'Nonlocality, Counterfactuals and Quantum Mechanics'
Stapp, H.P.
1999-04-14T23:59:59.000Z
A recent proof [H. P. Stapp, Am. J. Phys. 65, 300 (1997)], formulated in the symbolic language of modal logic, claims to show that contemporary quantum theory, viewed as a set of rules that allow us to calculate statistical predictions among certain kinds of observations, cannot be imbedded in any rational framework that conforms to the principles that (1) the experimenters' choices of which experiments they will perform can be considered to be free choices, (2) outcomes of measurements are unique, and (3) the free choices just mentioned have no backward-in-time effects of any kind. This claim is similar to Bell's theorem, but much stronger, because no reality assumption alien to quantum philosophy is used. The paper being commented on [W. Unruh, Phys. Rev. A 59, 126 (1999)] argues that some such reality assumption has been ''smuggled'' in. That argument is examined here and shown, I believe, to be defective.
Model checking quantum Markov chains
Yuan Feng; Nengkun Yu; Mingsheng Ying
2013-11-14T23:59:59.000Z
Although the security of quantum cryptography is provable based on the principles of quantum mechanics, it can be compromised by the flaws in the design of quantum protocols and the noise in their physical implementations. So, it is indispensable to develop techniques of verifying and debugging quantum cryptographic systems. Model-checking has proved to be effective in the verification of classical cryptographic protocols, but an essential difficulty arises when it is applied to quantum systems: the state space of a quantum system is always a continuum even when its dimension is finite. To overcome this difficulty, we introduce a novel notion of quantum Markov chain, specially suited to model quantum cryptographic protocols, in which quantum effects are entirely encoded into super-operators labelling transitions, leaving the location information (nodes) being classical. Then we define a quantum extension of probabilistic computation tree logic (PCTL) and develop a model-checking algorithm for quantum Markov chains.
Model checking quantum Markov chains
Feng, Yuan; Ying, Mingsheng
2012-01-01T23:59:59.000Z
Although the security of quantum cryptography is provable based on the principles of quantum mechanics, it can be compromised by the flaws in the design of quantum protocols and the noise in their physical implementations. So, it is indispensable to develop techniques of verifying and debugging quantum cryptographic systems. Model-checking has proved to be effective in the verification of classical cryptographic protocols, but an essential difficulty arises when it is applied to quantum systems: the state space of a quantum system is always a continuum even when its dimension is finite. To overcome this difficulty, we introduce a novel notion of quantum Markov chain, specially suited to model quantum cryptographic protocols, in which quantum effects are entirely encoded into super-operators labelling transitions, leaving the location information (nodes) being classical. Then we define a quantum extension of probabilistic computation tree logic (PCTL) and develop a model-checking algorithm for quantum Markov c...
Thermalization in Quantum Systems
of equilibrated states. iv. Definition for "quantum integrability". v. Many-body localization... vi. Open systems () 0 = ||2 . ETH: is approximately constant in the "energy window" of the state . ETH: For all 10 #12;Integrability 101 Quantum Integrability Classical systems: Definition: A system is integrable
Lucien Hardy
2012-06-14T23:59:59.000Z
In this paper we consider theories in which reality is described by some underlying variables. Each value these variables can take represents an ontic state (a particular state of reality). The preparation of a quantum state corresponds to a distribution over the ontic states. If we make three basic assumptions, we can show that the distributions over ontic states corresponding to distinct pure states are non-overlapping. This means that we can deduce the quantum state from a knowledge of the ontic state. Hence, if these assumptions are correct, we can claim that the quantum state is a real thing (it is written into the underlying variables that describe reality). The key assumption we use in this proof is ontic indifference - that quantum transformations that do not affect a given pure quantum state can be implemented in such a way that they do not affect the ontic states in the support of that state. In fact this assumption is violated in the Spekkens toy model (which captures many aspects of quantum theory and in which different pure states of the model have overlapping distributions over ontic states). This paper proves that ontic indifference must be violated in any model reproducing quantum theory in which the quantum state is not a real thing. The argument presented in this paper is different from that given in a recent paper by Pusey, Barrett, and Rudolph. It uses a different key assumption and it pertains to a single copy of the system in question.
Evgeny G. Fateev
2013-01-20T23:59:59.000Z
In a popular language, the possibilities of the Casimir expulsion effect are presented, which can be the basis of quantum motors. Such motors can be in the form of a special multilayer thin film with periodic and complex nanosized structures. Quantum motors of the type of the Casimir platforms can be the base of transportation, energy and many other systems in the future.
Svozil, Karl [Institut fuer Theoretische Physik, University of Technology Vienna, Wiedner Hauptstrasse 8-10/136, A-1040 Vienna (Austria)
2004-03-01T23:59:59.000Z
We consider sets of quantum observables corresponding to eutactic stars. Eutactic stars are systems of vectors which are the lower-dimensional 'shadow' image, the orthogonal view, of higher-dimensional orthonormal bases. Although these vector systems are not comeasurable, they represent redundant coordinate bases with remarkable properties. One application is quantum secret sharing.
Sanyal, Devashish [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700032 (India)]. E-mail: tpds@mahendra.iacs.res.in; Sen, Siddhartha [School of Mathematics, Trinity College, Dublin 2 (Ireland)]. E-mail: sen@maths.tcd.ie
2006-06-15T23:59:59.000Z
The present manuscript dealing with large occupation of states of a quantum system, extends the study to the case of quantum weak turbulence. The quasiparticle spectrum, calculated for such a system, using a Green's function approach, establishes the dissipative and inertial regimes, hence a Kolmogorov type of picture.
Feedback generation of quantum Fock states by discrete QND measures
Mazyar Mirrahimi; Igor Dotsenko; Pierre Rouchon
2009-05-04T23:59:59.000Z
A feedback scheme for preparation of photon number states in a microwave cavity is proposed. Quantum Non Demolition (QND) measurement of the cavity field provides information on its actual state. The control consists in injecting into the cavity mode a microwave pulse adjusted to maximize the population of the desired target photon number. In the ideal case (perfect cavity and measures), we present the feedback scheme and its detailed convergence proof through stochastic Lyapunov techniques based on super-martingales and other probabilistic arguments. Quantum Monte-Carlo simulations performed with experimental parameters illustrate convergence and robustness of such feedback scheme.
Rotation in classical zero-point radiation and in quantum vacuum
Yefim S. Levin
2006-06-02T23:59:59.000Z
Two reference systems (RS) are defined and used as the basis for investigating thermal effects of rotation through both random classical zero point radiation and quantum vacuum. Both RSs consist of an infinite number of instantaneous global inertial reference frames (RF). The RFs do not accompany the detector and are defined so that at each moment of proper time of the detector there are two RFs belonging with different RSs. These RFs agree momentarily, are connected by a Lorentz transformation with the detector velocity as a parameter, and with origins at the detector location at the same proper time. The two- field correlation functions (CF) measured by the observer rotating through a random classical zero point radiation have been calculated and presented in terms of elementary functions for both electromagnetic and massless scalar fields. If the CFs are periodic with a period of rotation the observer finds the spectrum which is very similar, but not identical, to Plank spectrum. If both fields of such a two-field periodic CF, for both electromagnetic and massless scalar case, are taken at the same point then its convergent part is shown, using Abel-Plana summation formula, to have Planck spectrum with the temperature T= hw/k, where w is an angular velocity of the detector. It is shown that the vacuum of the quantized massless scalar field in rotating RS is not equivalent to the vacuum of the field in the laboratory system because the respective Bogolubov transformation is not a zero.
Permutational Quantum Computing
Stephen P. Jordan
2009-06-14T23:59:59.000Z
In topological quantum computation the geometric details of a particle trajectory are irrelevant; only the topology matters. Taking this one step further, we consider a model of computation that disregards even the topology of the particle trajectory, and computes by permuting particles. Whereas topological quantum computation requires anyons, permutational quantum computation can be performed with ordinary spin-1/2 particles, using a variant of the spin-network scheme of Marzuoli and Rasetti. We do not know whether permutational computation is universal. It may represent a new complexity class within BQP. Nevertheless, permutational quantum computers can in polynomial time approximate matrix elements of certain irreducible representations of the symmetric group and simulate certain processes in the Ponzano-Regge spin foam model of quantum gravity. No polynomial time classical algorithms for these problems are known.
High Performance Quantum Computing
Simon J. Devitt; William J. Munro; Kae Nemoto
2008-10-14T23:59:59.000Z
The architecture scalability afforded by recent proposals of a large scale photonic based quantum computer, utilizing the theoretical developments of topological cluster states and the photonic chip, allows us to move on to a discussion of massively scaled Quantum Information Processing (QIP). In this letter we introduce the model for a secure and unsecured topological cluster mainframe. We consider the quantum analogue of High Performance Computing, where a dedicated server farm is utilized by many users to run algorithms and share quantum data. The scaling structure of photonics based topological cluster computing leads to an attractive future for server based QIP, where dedicated mainframes can be constructed and/or expanded to serve an increasingly hungry user base with the ideal resource for individual quantum information processing.
Pachucki, Krzysztof
Proton charge radius and the perturbative quantum electrodynamics Krzysztof Pachucki and Krzysztof that the proton charge radius conundrum can be resolved by weakening the assumption of pertur- bative formulation of quantum electrodynamics within the proton. PACS numbers: 12.20.-m, 13.60.-r, 31.30.jr The proton radius
Schofield, Jeremy
Quantum free-energy differences from nonequilibrium path integrals. II. Convergence properties July 2008; published 2 October 2008 Nonequilibrium path-integral methods for computing quantum free-energy with the purpose of establishing the convergence properties of the work distribution and free energy as the number
Quantum secret sharing schemes and reversibility of quantum operations
Ogawa, Tomohiro [Graduate School of Information Science and Technology, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 (Japan); Sasaki, Akira [Sumitomo Mitsui Banking Corporation, 1-3-2, Marunouchi, Chiyoda-ku, Tokyo 100-0005 (Japan); Iwamoto, Mitsugu [Graduate School of Information Systems, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu-shi, Tokyo, 182-8585 (Japan); Yamamoto, Hirosuke [Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba, 277-8561 (Japan)
2005-09-15T23:59:59.000Z
Quantum secret sharing schemes encrypting a quantum state into a multipartite entangled state are treated. The lower bound on the dimension of each share given by Gottesman [Phys. Rev. A 61, 042311 (2000)] is revisited based on a relation between the reversibility of quantum operations and the Holevo information. We also propose a threshold ramp quantum secret sharing scheme and evaluate its coding efficiency.
Quantum theory Bohrification: topos theory and quantum theory
Spitters, Bas
Quantum theory Bohrification: topos theory and quantum theory Bas Spitters Domains XI, 9/9/2014 Bas Spitters Bohrification: topos theory and quantum theory #12;Quantum theory Point-free Topology The axiom, Krein-Millman, Alaoglu, Hahn-Banach, Gelfand, Zariski, ... Bas Spitters Bohrification: topos theory
Universal blind quantum computation
Anne Broadbent; Joseph Fitzsimons; Elham Kashefi
2009-12-12T23:59:59.000Z
We present a protocol which allows a client to have a server carry out a quantum computation for her such that the client's inputs, outputs and computation remain perfectly private, and where she does not require any quantum computational power or memory. The client only needs to be able to prepare single qubits randomly chosen from a finite set and send them to the server, who has the balance of the required quantum computational resources. Our protocol is interactive: after the initial preparation of quantum states, the client and server use two-way classical communication which enables the client to drive the computation, giving single-qubit measurement instructions to the server, depending on previous measurement outcomes. Our protocol works for inputs and outputs that are either classical or quantum. We give an authentication protocol that allows the client to detect an interfering server; our scheme can also be made fault-tolerant. We also generalize our result to the setting of a purely classical client who communicates classically with two non-communicating entangled servers, in order to perform a blind quantum computation. By incorporating the authentication protocol, we show that any problem in BQP has an entangled two-prover interactive proof with a purely classical verifier. Our protocol is the first universal scheme which detects a cheating server, as well as the first protocol which does not require any quantum computation whatsoever on the client's side. The novelty of our approach is in using the unique features of measurement-based quantum computing which allows us to clearly distinguish between the quantum and classical aspects of a quantum computation.
Virendra Singh
2005-10-24T23:59:59.000Z
We review here the main contributions of Einstein to the quantum theory. To put them in perspective we first give an account of Physics as it was before him. It is followed by a brief account of the problem of black body radiation which provided the context for Planck to introduce the idea of quantum. Einstein's revolutionary paper of 1905 on light-quantum hypothesis is then described as well as an application of this idea to the photoelectric effect. We next take up a discussion of Einstein's other contributions to old quantum theory. These include (i) his theory of specific heat of solids, which was the first application of quantum theory to matter, (ii) his discovery of wave-particle duality for light and (iii) Einstein's A and B coefficients relating to the probabilities of emission and absorption of light by atomic systems and his discovery of radiation stimulated emission of light which provides the basis for laser action. We then describe Einstein's contribution to quantum statistics viz Bose-Einstein Statistics and his prediction of Bose-Einstein condensation of a boson gas. Einstein played a pivotal role in the discovery of Quantum mechanics and this is briefly mentioned. After 1925 Einstein's contributed mainly to the foundations of Quantum Mechanics. We choose to discuss here (i) his Ensemble (or Statistical) Interpretation of Quantum Mechanics and (ii) the discovery of Einstein-Podolsky-Rosen (EPR) correlations and the EPR theorem on the conflict between Einstein-Locality and the completeness of the formalism of Quantum Mechanics. We end with some comments on later developments.
Global quantum discord and quantum phase transition in XY model
Si-Yuan Liu; Yu-Ran Zhang; Wen-Li Yang; Heng Fan
2014-05-20T23:59:59.000Z
We study the relationship between the behavior of global quantum correlations and quantum phase transitions in XY model. We find that the two kinds of phase transitions in the studied model can be characterized by the features of global quantum discord (GQD) and the corresponding quantum correlations. We demonstrate that the maximum of the sum of all the nearest neighbor bipartite GQDs is effective and accurate for signaling the Ising quantum phase transition, in contrast, the sudden change of GQD is very suitable for characterizing another phase transition in the XY model. This may shed lights on the study of properties of quantum correlations in different quantum phases.