Macroscopic Quantum Effects In Bose-Einstein Condensates

In 1995, Ketterle, Wieman and Cornell et al. first realized the Bose-Einstein condensations in the dilute trapped alkali-metal atom gases which were predicted by Einstein eighty years ago. It was a new milestone in the research history of the atomic and molecular physics in low temperature. Till now, physicist have investigated Bose- Einstein condensations by mean of the methods from the atomic physics, the quantum optics, the condensed matter physics, the nuclear physics and astrophysics, therefore the investigation of the Bose-Einstein condensations became a focus field to the physical scientists.In this thesis, by using the semi-classical theory combined with the two mode approximation method, we study the macroscopic quantum tunneling phenomena in two weak -interacting Bose-Einstein condensations and obtain a serial of valuable results. The thesis consists of five chapters: In chapter one, we introduce the elementary content of the Bose-Einstein condensation and the correlated experiments. Chapter two is illuminated the basic methods of the macroscopic quantum phenomena in the two weak-interacting Bose-Einstein condensations. In chapter three, based on the two mode approximation method combined with the semi-classical theory, we study the dynamical properties in the asymmetric Josephson junction of the two weak-interacting Bose-Einstein condensates and then numericallysimulate the dynamical behaves. And the properties of the zero-phase modes and n -phase modes were obtained. In chapter four, we propose the dynamical equations of the Josephson junction of the two weak-interacting BECs in the periodical potential and study their dynamic properties by developing semi-classical theory combined with numerical simulation. It is shown that the stably dynamical conditions were determined by the initial states and the ratio of the two ground statics energies and the interaction energies. In the final chapter, we summarize the present paper and give an outlook of the future study in this field.