Kosterlitz-Thouless Transition of the Quasi-Two-Dimensional Trapped Bose Gas

Werner Krauth
École Normale Supérieure

We use quantum Monte Carlo methods to compute the density profile, the nonclassical moment of inertia, and the condensate fraction of an interacting quasi-two-dimensional trapped Bose gas with up to one million particles, and parameters closely related to recent experiments.
We locate the Kosterlitz-Thouless transition temperature T_KT, and discuss intrinsic signatures of the onset of superfluidity in the density profile. Above T_KT, the system can be described very accurately by a semiclassical theory taking into account the transverse degrees of freedom, but it differs notably from the strictly two-dimensional case. Below T_KT, the condensate fraction is macroscopic even for our largest systems, and it decays only slowly with system size. We discuss the relevance of our findings for analyzing ulta-cold-atom experiments in quasi-two-dimensional traps.

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