Connecting Berezinskii-Kosterlitz-Thouless and BEC phase transitions by tuning interactions in a trapped gas

TL;DR

This study experimentally connects the BKT and BEC phase transitions in a 2D trapped Bose gas by tuning interactions, confirming theoretical predictions and showing a smooth transition between the two phenomena.

Contribution

It demonstrates the continuous connection between BKT and BEC transitions in a controlled experimental setting with tunable interactions.

Findings

Excellent agreement with classical-field predictions for BKT critical point.

Interaction-driven BKT transition converges to BEC transition as interactions vanish.

Quantitative, parameter-free validation of the transition connection.

Abstract

We study the critical point for the emergence of coherence in a harmonically trapped two-dimensional Bose gas with tuneable interactions. Over a wide range of interaction strengths we find excellent agreement with the classical-field predictions for the critical point of the Berezinskii-Kosterlitz-Thouless (BKT) superfluid transition. This allows us to quantitatively show, without any free parameters, that the interaction-driven BKT transition smoothly converges onto the purely quantum-statistical Bose-Einstein condensation (BEC) transition in the limit of vanishing interactions.