Towards quantum information processing with impurity spins insilicon
The finding of algorithms for factoring and data base search that promise substantially increased computational power, as well as the expectation for efficient simulation of quantum systems have spawned an intense interest in the realization of quantum information processors [1]. Solid state implementations of quantum computers scaled to >1000 quantum bits ('qubits') promise to revolutionize information technology, but requirements with regard to sources of decoherence in solid state environments are sobering. Here, we briefly review basic approaches to impurity spin based qubits and present progress in our effort to form prototype qubit test structures. Since Kane's bold silicon based spin qubit proposal was first published in 1998 [2], several groups have taken up the challenge of fabricating elementary building blocks [3-5], and several exciting variations of single donor qubit schemes have emerged [6]. Single donor atoms, e. g. {sup 31}P, are 'natural quantum dots' in a silicon matrix, and the spins of electrons and nuclei of individual donor atoms are attractive two level systems for encoding of quantum information. The coupling to the solid state environment is weak, so that decoherence times are long (hours for nuclear spins, and {approx}60 ms for electron spins of isolated P atoms in silicon [7]), while control over individual spins for one qubit operations becomes possible when individual qubits are aligned to electrodes that allow shifting of electron spin resonances in global magnetic fields by application of control voltages. Two qubit operations require an interaction that couples, and entangles qubits. The exchange interaction, J, is a prime candidate for mediation of two qubit operations, since it can be turned on and off by variation of the wave function overlap between neighboring qubits, and coherent manipulation of quantum information with the exchange interaction alone has been shown to be universal [8]. However, detailed band structure calculations and theoretical analysis of J coupling between electrons bound to phosphorus atoms at low temperatures in silicon revealed strong oscillations of the coupling strength as a function of donor spacing on a sub-nm length scale [9]. These oscillations translate into scattering of interaction strength for ensembles of qubit spacings which in turn poses a serious obstacle to scalability [10]. Two alternatives to J coupling are dipolar coupling [11] and spin coherent shuttling of electrons between donor sites [12]. Readout of single electron spins poses another critical challenge [13, 14], and inferring spin orientations from charge measurements in spin dependent charge transfer reactions seems to be viable route to single shot single spin readout. This readout can be accomplished with single electron transistors, which are used as sensitive electrometers [15]. Impurity spin based qubit schemes in silicon have to overcome a significant nanofabrication challenge so that a test bed regime can be entered where fundamental properties and rudimentary operations can be investigated. In order to form such test devices, three key components have to be integrated: (1) an array of single dopant atoms has to be formed; (2) single dopant atoms are aligned to control gates; and (3) single dopant atoms are also aligned to a readout device.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 924830
- Report Number(s):
- LBNL-54449; R&D Project: 43GW04; BnR: 400403909; TRN: US0802988
- Resource Relation:
- Conference: 2004 American Vacuum Society (AVS) 5thInternational Conference on Microelectronics, and Interfaces, SantaClara, CA, March 1-3, 2004
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
70
ALGORITHMS
ATOMS
ELECTRODES
ELECTROMETERS
ELECTRON SPIN RESONANCE
ELECTRONS
EXCHANGE INTERACTIONS
MAGNETIC FIELDS
MICROELECTRONICS
NUCLEI
OSCILLATIONS
PHOSPHORUS
QUANTUM COMPUTERS
QUANTUM INFORMATION
QUBITS
SILICON
SPIN
SPIN ORIENTATION
TRANSFER REACTIONS
TRANSISTORS
WAVE FUNCTIONS
quantum computer spins quantum information processing