Matter wave interferometry with phase fluctuating condensates*

We report on the thermal phase fluctuations in condensates trapped on atom chips and address the question of robustness of chip-based BEC interferometry against phase fluctuations. Since quasi-1D condensates created on atom chips are typically in the phase fluctuating regime with a phase coherence length shorter than the spatial extent of the cloud, the presence of the fluctuation may degrade interference fringes and, consequently, erase the relative phase information in the fringes. In the experiment, we produce a double-well potential in the plane parallel to {\bf g} by deforming a single well using adiabatic rf-induced splitting. We observe a decrease in the fringe contrast as the temperature increases, indicating that fringes become wavier at higher temperature. We also discuss the effect of fluctuations on the phase coherence of the split condensates.