Coherence and Correlations in Systems of Cold Atoms

Wolfgang Belzig

W. Belzig, C. Schroll, and C. Bruder
Institute of Physics, University of Basel, Klingelbergstr. 82, 4056 Basel, Switzerland

We investigate two aspects of fluctuation phenomena in coherent matter waves. First, current carrying wires used on atomic chips cause intrinsic current fluctuations, which lead to a dephasing in the coherent propagation of matter waves. Using a stochastic approach to the density matrix time evolution we find the conditions under which interference should be observable and make quantitative predictions for the observed interference pattern. Second, we investigate density fluctuations in a coherent ensemble of Fermionic atoms around the BEC-BCS crossover. Adapting the concept of full counting statistics, well know from quantum optics and mesoscopic electron transport, we study second-order as well as higher-order correlators of density fluctuations. This method is applied to the crossover from a fermionic BCS state to a molecular BEC state and yields a transition from binomial statistics to Poisson statistics.