Coherence length of an elongated condensate: a study by matter-wave   interferometry
  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. 
Mathilde Hugbart (LCFIO), Jocelyn Retter (LCFIO), Fabrice Gerbier,   Andres Varon (LCFIO), Simon Richard, Joseph Thywissen, ...