Spatial analysis phase fluctuating Bose-Einstein condensates

The phase correlation properties of elongated BECs are studied in detail. It is shown that at finite temperature, the phase of the BEC is not uniform but undergoes statistical fluctuations. In particular, we observe BECs where the phase coherence length is smaller than the condensate size, i.e. so called quasicondensates. Recent interferometric measurement of the coherence length in the regime where strong phase fluctuations are present in the condensates is reported. The method is compared to complementary ways of measuring the coherence length. The possibility of a complete numerical phase reconstruction from time-of-flight images is evaluated.