Two-point density correlations of quasicondensates in free expansion

TL;DR

This study measures how density correlations develop in freely expanding 1D quasicondensates, revealing their relation to initial phase fluctuations and thermal coherence, with implications for thermometry.

Contribution

It provides experimental validation of theoretical models describing density correlations during expansion in 1D quasicondensates, highlighting their use for thermometry.

Findings

Density fluctuations emerge during expansion from initial phase fluctuations.

Good agreement with theoretical predictions by Imambekov et al.

Density correlations can serve as a thermometric tool.

Abstract

We measure the two-point density correlation function of freely expanding quasicondensates in the weakly interacting quasi-one-dimensional (1D) regime. While initially suppressed in the trap, density fluctuations emerge gradually during expansion as a result of initial phase fluctuations present in the trapped quasicondensate. Asymptotically, they are governed by the thermal coherence length of the system. Our measurements take place in an intermediate regime where density correlations are related to near-field diffraction effects and anomalous correlations play an important role. Comparison with a recent theoretical approach described by Imambekov et al. yields good agreement with our experimental results and shows that density correlations can be used for thermometry of quasicondensates.