Coherence properties of a 2D trapped Bose gas around the superfluid transition

TL;DR

This paper investigates the coherence properties of a 2D trapped Bose gas near the superfluid transition, revealing increased coherence range and comparing experimental data with theoretical models.

Contribution

It provides the first detailed measurement of momentum distribution changes across the BKT transition in a 2D Bose gas, comparing results with mean-field and Monte Carlo theories.

Findings

Increased coherence range near the BKT transition

Sharpening of momentum distribution in the normal phase

Partial agreement with mean-field theory outside the transition

Abstract

We measure the momentum distribution of a 2D trapped Bose gas and observe the increase of the range of coherence around the Berezinskii-Kosterlitz-Thouless (BKT) transition. We quantitatively compare our observed profiles to both a Hartee-Fock mean-field theory and to quantum Monte-Carlo simulations. In the normal phase, we already observe a sharpening of the momentum distribution. This behavior is partially captured in a mean-field approach, in contrast to the physics of the BKT transition.