| Abstract |
I investigated the creation of coherent atomic ensembles by various means, all of which are either already demonstrated experimentally or within reach of current experiments. I investigated the dynamics of the outcoupling of a coherent beam from an atomic Bose-Einstein condensate. Since this problem is well treated in present literature, I focused on another aspect of proposed atom-laser schemes, the pumping. To this end, I investigated the merging of independent condensates and paid particular attention to the role of the relative phase. I found that it emerges as a key parameter during the merging process, almost solely defining the resulting dynamics. More concretely, the phase difference determines the depth of an adiabatically formed soliton as well as the dynamics of a dipole oscillation of the atomic cloud which builds up during the merging process. Under the assumption of a coherent cooling, such as evaporation of higher energy atoms from the ensemble, I was able to empirically find an analytic formula for the phase of the final condensate. I studied the merging as an independent process, not necessarily linked to the atom laser itself. My results might shed light on new, non-destructive ways of reading out phase differences between condensates as it is necessary in matter-wave interferometry. I also turned towards a different way of producing matter-wave pulses altogether, namely superradiance from condensates, which shows other promising aspects, such as well defined populations and momenta of the created pulses. I constructed a quantum treatment for the early stages of the process which is not well described within the available mean-field models. This semiclassical model can, however, produce quantum expectation values by means of averaging over randomly seeded trajectories. I used these relations to investigate the statistics of delay- and passage-times of superradiant pulses. Beyond the mean-field treatment of the problem, the quantum model predicts long-range order as well as atomic bunching in the sidemodes and enhanced cross-correlations between forward and backward scattered atoms. In the strong-pulse regime, the two counterpropagating clouds become entangled and their number difference is squeezed.
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Dynamics of atomic Bose-Einstein condensates and the atom laser
