Revealing single-trap condensate fragmentation by measuring density-density correlations after time of flight

TL;DR

This paper shows that measuring density-density correlations after free expansion can uniquely identify fragmentation in ultracold bosonic condensates within a single trap, providing a new experimental signature.

Contribution

It introduces a method to detect condensate fragmentation by analyzing the spatial dependence of correlations after time of flight.

Findings

Correlation signals differ between fragmented and nonfragmented condensates.

Time of flight modifies correlation patterns, revealing fragmentation.

Opposite points in the cloud become uncorrelated only in fragmented states.

Abstract

We consider ultracold bosonic atoms in a single trap in the Thomas-Fermi regime, forming many-body states corresponding to stable macroscopically fragmented two-mode condensates. It is demonstrated that upon free expansion of the gas, the spatial dependence of the density-density correlations at late times provides a unique signature of fragmentation. This hallmark of fragmented condensate many-body states in a single trap is due to the fact that time of flight modifies the correlation signal such that two opposite %with respect to points in the expanding cloud become uncorrelated, in distinction to a nonfragmented Bose-Einstein condensate, where they remain correlated.