Interference of Bose condensates
  We investigate the prospects of atomic interference using samples of Bose condensed atoms. First we show the ability of two independent Bose condensates to create an interference pattern, even if both condensates are described by Fock states. Thus, the existence of an experimental signature for a broken gauge symmetry, seen in a single run of the experiment, is not necessarily reflected by a broken symmetry on the level of the quantum mechanical state vector. Based on these results, we simulate numerically a recent experiment with two independent Bose condensates, performed by the group of W.Ketterle (MIT). The calculated expansion of the condensates is in good agreement with the experimental data. In addition the existence of interference fringes is predicted based on the nonlinear Schroedinger equation. Finally we study theoretically the influence of finite temperatures on the visibility of the interference in a double pinhole experiment. 
M. Naraschewski, H. Wallis, A. Schenzle (MPI f. Quantenoptik), J.I.   Cirac (Universidad de Castilla-La Mancha), and P. Zoll...