Observation of phase fluctuations in elongated Bose-Einstein condensates -art. no. 160406

The occurrence of phase fluctuations due to thermal excitations in Bose-Ein stein condensates (BECs) is studied for a variety of temperatures and trap geometries. We observe the statistical nature of the appearance of phase fl uctuations and characterize the dependence of their average value on temper ature, number of particles, and the trapping potential. We find pronounced phase fluctuations for condensates in very elongated traps in a broad tempe rature range. The results are of great importance for the realization of BE C in quasi-ID geometries, for matter wave interferometry with BECs, as well as for coherence properties of guided atom laser beams.