The Coherence Of A Dipolar Condensate In A Harmonic Potential Superimposed To A Deep Lattice

Optical lattices are ideal candidates for investigating the fundamental physics of quantum gas and can be used to manipulate the dynamics of the condensate. Abundant, controllable coherence-decoherence transitions can be achieved by condensate restricted in optical lattices. Because of the exquisite controllability of interaction, interaction is frequently used in regulating and controlling ultracold Bose gas. When a dipolar Bose gas loaded in a deep optical lattices, the most evident effect of the optical lattices is the oc-currence of Bloch oscillations. Besides its fundamental significance, the Bloch oscillation can be used to complete the high-precision measurements. However, atom interaction-induced decoherence limits the observation of Bloch oscillations to a few cycles and gives rise to density-dependent mean-filed shift in the interferometric signal. Recently, the interaction-induce decoherence can be reduced significantly in a usual short-range inter-acting BEC-based interferometer. The magnetic dipole-dipole interaction between the atoms provides the possibility of coherence for the Bloch oscillation, which is confirmed by the experiment. So how can we come up with appropriate values of the contact inter-action and dipole interaction for controlling the decoherence of Bloch oscillations is very important. Moreover, the parameters of the potential for the lattice also affect the de-coherence of Bloch oscillations. Moreover, the parameters of the potential for the lattice also affect the decoherence of Bloch oscillations, especially, in the optical lattice with a disorder potential. In particular, it is found that, while disorder or interaction suppresses the coherence by itself, the cooperation of disorder and interaction can enhance the co-herence of the system. Therefore, we should design appropriate magnitude of disorder and interaction to control the decoherence of Bloch oscillations.In the first chapter, the physical background and the related physical knowledge are briefly introduced, including coherent destruction of optical lattices, Bloch oscilations and disorder.In the second chapter, within the mean-field Bose-Hubbard model, the coherent matter waves of a dipolar condensates in optical lattices with two kinds of harmonic trap potential are investigated by the variational principle. It is shown that, in an optical lattices with a harmonic potential without disorder, it is possible to control the deco-herence of Bloch oscillations because on-site interaction and inter-site dipolar interaction can not only damp out Bloch oscillations but also maintain long-lived Bloch oscillations. In particular, long-lived Bloch oscillations of dipolar oscillations can be realized when the dipolar interaction, the contact interaction, the frequency of harmonic potential and initial width of wave packet satisfy an analytical condition. Furthermore, in an optical lattices with disorder harmonic potential, disorder has an important effect on the deco-herence of Bloch oscillations. Thus the decoherence of Bloch oscillation can be controlled by adjusting intensity of disorder.Finally, we summarize the main results and give an outlook of the future in this field.