Revealing single-trap condensate fragmentation by measuring   density-density correlations after time of flight
  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. 
Myung-Kyun Kang and Uwe R. Fischer
cond-mat.quant-gas quant-ph