Detecting Phase Coherence of 2D Bose Gases via Noise Correlations

TL;DR

This paper demonstrates how noise correlations in 2D Bose gases can be used to detect phase coherence and identify the BKT transition, providing a new experimental tool for studying quantum many-body states.

Contribution

It introduces noise interferometry as a novel method to characterize phase coherence and the BKT transition in 2D Bose gases, including in multi-layer systems.

Findings

Noise correlations reveal oscillatory behavior in the superfluid phase.

Oscillatory behavior disappears above the BKT transition.

Method applies to both single-layer and bilayer systems.

Abstract

We measure the noise correlations of two-dimensional (2D) Bose gases after free expansion, and use them to characterize the in-situ phase coherence across the Berezinskii-Kosterlitz-Thouless (BKT) transition. The noise-correlation function features a characteristic spatial oscillatory behavior in the superfluid phase, which gives direct access to the superfluid exponent. This oscillatory behavior vanishes above the BKT critical point, as we demonstrate for both single-layer and decoupled bilayer 2D Bose gases. Our work establishes noise interferometry as an important general tool to probe and identify many-body states of quantum gases, extending its application to previously inaccessible correlation properties in multimode systems.