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Title: Antiblockade in Rydberg Excitation of an Ultracold Lattice Gas

Abstract

It is shown that the two-step excitation scheme typically used to create an ultracold Rydberg gas can be described with an effective two-level rate equation, greatly reducing the complexity of the optical Bloch equations. This allows us to efficiently solve the many-body problem of interacting cold atoms with a Monte Carlo technique. Our results reproduce the observed excitation blockade effect. However, we demonstrate that an Autler-Townes double peak structure in the two-step excitation scheme, which occurs for moderate pulse lengths as used in the experiment, can give rise to an antiblockade effect. It is most pronounced for atoms arranged on a lattice. Since the effect is robust against a large number of lattice defects it should be experimentally realizable with an optical lattice created by CO{sub 2} lasers.

Authors:
; ;  [1];  [2]
  1. Max Planck Institute for the Physics of Complex Systems, Noethnitzer Strasse 38, D-01187 Dresden (Germany)
  2. ITAMP, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)
Publication Date:
OSTI Identifier:
20861597
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 2; Other Information: DOI: 10.1103/PhysRevLett.98.023002; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; BLOCH EQUATIONS; CARBON DIOXIDE LASERS; CRYSTAL DEFECTS; EXCITATION; MANY-BODY PROBLEM; MONTE CARLO METHOD; RYDBERG STATES

Citation Formats

Ates, C., Pattard, T., Rost, J. M., and Pohl, T.. Antiblockade in Rydberg Excitation of an Ultracold Lattice Gas. United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.023002.
Ates, C., Pattard, T., Rost, J. M., & Pohl, T.. Antiblockade in Rydberg Excitation of an Ultracold Lattice Gas. United States. doi:10.1103/PHYSREVLETT.98.023002.
Ates, C., Pattard, T., Rost, J. M., and Pohl, T.. Fri . "Antiblockade in Rydberg Excitation of an Ultracold Lattice Gas". United States. doi:10.1103/PHYSREVLETT.98.023002.
@article{osti_20861597,
title = {Antiblockade in Rydberg Excitation of an Ultracold Lattice Gas},
author = {Ates, C. and Pattard, T. and Rost, J. M. and Pohl, T.},
abstractNote = {It is shown that the two-step excitation scheme typically used to create an ultracold Rydberg gas can be described with an effective two-level rate equation, greatly reducing the complexity of the optical Bloch equations. This allows us to efficiently solve the many-body problem of interacting cold atoms with a Monte Carlo technique. Our results reproduce the observed excitation blockade effect. However, we demonstrate that an Autler-Townes double peak structure in the two-step excitation scheme, which occurs for moderate pulse lengths as used in the experiment, can give rise to an antiblockade effect. It is most pronounced for atoms arranged on a lattice. Since the effect is robust against a large number of lattice defects it should be experimentally realizable with an optical lattice created by CO{sub 2} lasers.},
doi = {10.1103/PHYSREVLETT.98.023002},
journal = {Physical Review Letters},
number = 2,
volume = 98,
place = {United States},
year = {Fri Jan 12 00:00:00 EST 2007},
month = {Fri Jan 12 00:00:00 EST 2007}
}
  • In cold dense Rydberg atom samples, the dipole-dipole interaction strength is effectively resonant at the typical interatomic spacing in the sample, and the interaction has a 1/R{sup 3} dependence on interatomic spacing R. The dipole-dipole attraction leads to ionizing collisions of initially stationary atoms, which produces hot atoms and ions and initiates the evolution of initially cold samples of neutral Rydberg atoms into plasmas. More generally, the strong dipole-dipole forces lead to motion, which must be considered in proposed applications.
  • We develop a theoretical approach for the dynamics of Rydberg excitations in ultracold gases,with a realistically large number of atoms. We rely on the reduction of the single-atom Bloch equations to rate equations, which is possible under various experimentally relevant conditions. Here, we explicitly refer to a two-step excitation scheme. We discuss the conditions under which our approach is valid by comparing the results with the solution of the exact quantum master equation for two interacting atoms. Concerning the emergence of an excitation blockade in a Rydberg gas, our results are in qualitative agreement with experiment. Possible sources of quantitativemore » discrepancy are carefully examined. Based on the two-step excitation scheme, we predict the occurrence of an antiblockade effect and propose possible ways to detect this excitation enhancement experimentally in an optical lattice, as well as in the gas phase.« less
  • We propose a method for the determination of the interaction potential of Rydberg atoms. Specifically, we consider a laser-driven Rydberg gas confined in a one-dimensional lattice and demonstrate that the Rydberg atom number after a laser excitation cycle as a function of the laser detuning provides a measure for the Rydberg interaction coefficient. With the lattice spacing precisely known, the proposed scheme only relies on the measurement of the number of Rydberg atoms and thus circumvents the necessity to map the interaction potential by varying the interparticle separation.
  • We present time-resolved spectroscopic measurements of Rydberg-Rydberg interactions between two Rydberg atoms in an ultracold gas, revealing the pair dynamics induced by long-range van der Waals interactions between the atoms. By detuning the excitation laser, a specific pair distribution is prepared. Penning ionization on a microsecond time scale serves as a probe for the pair dynamics under the influence of the attractive long-range forces. Comparison with a Monte Carlo model not only explains all spectroscopic features but also gives quantitative information about the interaction potentials. The results imply that the interaction-induced ionization rate can be influenced by the excitation laser.more » Surprisingly, interaction-induced ionization is also observed for Rydberg states with purely repulsive interactions.« less
  • We report the spontaneous formation of a plasma from a gas of cold Rydberg molecules. Double-resonant laser excitation promotes nitric oxide, cooled to 1 K in a seeded supersonic molecular beam, to single Rydberg states extending as deep as 80 cm{sup -1} below the lowest ionization threshold. The density of excited molecules in the illuminated volume approaches 1x10{sup 13} cm{sup -3}. This population evolves to produce free electrons and a durable cold plasma of electrons and intact NO{sup +} ions.