Vortex pairing in two-dimensional Bose gases

Christopher J. Foster, P. Blair Blakie, and Matthew J. Davis
Phys. Rev. A 81, 023623 – Published 24 February 2010

Abstract

Recent experiments on ultracold Bose gases in two dimensions have provided evidence for the existence of the Berezinskii-Kosterlitz-Thouless (BKT) phase via analysis of the interference between two independent systems. In this work we study the two-dimensional quantum degenerate Bose gas at finite temperature using the projected Gross-Pitaevskii equation classical field method. Although this describes the highly occupied modes of the gas below a momentum cutoff, we have developed a method to incorporate the higher momentum states in our model. We concentrate on finite-sized homogeneous systems in order to simplify the analysis of the vortex pairing. We determine the dependence of the condensate fraction on temperature and compare this to the calculated superfluid fraction. By measuring the first order correlation function we determine the boundary of the Bose-Einstein condensate and BKT phases, and find it is consistent with the superfluid fraction decreasing to zero. We reveal the characteristic unbinding of vortex pairs above the BKT transition via a coarse-graining procedure. Finally, we model the procedure used in experiments to infer system correlations [Hadzibabic et al., Nature 441, 1118 (2006)], and quantify its level of agreement with directly calculated in situ correlation functions.

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  • Received 9 December 2009

DOI:https://doi.org/10.1103/PhysRevA.81.023623

©2010 American Physical Society

Authors & Affiliations

Christopher J. Foster1, P. Blair Blakie2, and Matthew J. Davis1

  • 1The University of Queensland, School of Mathematics and Physics, ARC Centre of Excellence for Quantum-Atom Optics, Queensland 4072, Australia
  • 2The Jack Dodd Centre for Quantum Technology, Department of Physics, University of Otago, Dunedin, New Zealand

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Issue

Vol. 81, Iss. 2 — February 2010

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