Dynamics Of An Ultracold Dipolar Atom Gas In A Double Well

Bose-Einstein condensate as a new matter state has been an important research topic in ultracold atom physics and quantum optics since it was first realized in dilute alkali gases in 1995.Recently,after cooling and trapping ultracold Cr atom gases with larger magnetic dipoles has been realized in laboratory,the effect of dipole-dipole interaction on the dynamics of ultracold atom gases is emerging as a hot topic of intensive theoretical and experimental investigation.In this thesis,we have studied the effect of magnetic dipole-dipole interaction on the dynamics of ultracold atom gases in a double well.For a quasi-one-dimensional dipolar gas,we have derived the Gross-Pitaeskii equation with a magnetic dipole-dipole interaction and find a critical polarization direction along which the repulsive interaction and attractive interaction cancel out each other.The critical polarization direction can be used to control the dynamics of the ultracold polar gases in a double well.Solving the Gross-Pitaeskii equation numerically,we find that when the atomic dipolar polarization angle is smaller than the critical polarization angle,the wave function has a symmetrical bimodal distribution;when the atomic dipolar angle is greater than the critical polarization angle,the wave function localizes in one of the double wells,because the attractive dipole-dipole interaction dominates now and leads to spontaneous symmetry breaking.Raising the potential barrier to split a Bose-Einstein condensate into two matter waves is an important approach to realize an atomic matter wave interferometer.So we study the effect of the magnetic dipole-dipole interaction on the splitting process and find that when the polarization angle is larger than the critical polarization angle, non-adiabatically raising the potantial barrier produces two symmetrical matter waves; while adiabatically raising creates an asymmetrical matter wave. The spontaneous symmetry breaking phenomena found in our thesis could be applied to study atomic interferometer based on the ultracold dipolar gases trapped in a double well,and could be used to prepare a Schr(o|¨)dinger cat state.