Coherence length of an elongated condensate: a study by matter-wave interferometry

TL;DR

This study measures the coherence length of elongated Bose-Einstein condensates using matter-wave interferometry, revealing a smooth transition in phase coherence without a sharp boundary between different fluctuation regimes.

Contribution

It provides the first detailed experimental characterization of the continuous change in coherence length across phase-fluctuation regimes in elongated condensates.

Findings

Coherence length varies smoothly with temperature.

Transition from Gaussian to exponential correlation shape.

No sharp phase transition observed.

Abstract

We measure the spatial correlation function of Bose-Einstein condensates in the cross-over region between phase-coherent and strongly phase-fluctuating condensates. We observe the continuous path from a gaussian-like shape to an exponential-like shape characteristic of one-dimensional phase-fluctuations. The width of the spatial correlation function as a function of the temperature shows that the condensate coherence length undergoes no sharp transition between these two regimes.