中文摘要：

This paper studies theoretically the spin evolution of a Bose-Einstein condensate starting from a mixture of two or three groups of 52 Cr (spin-3) atoms in an optical trap.The initial state is so chosen that the condensate has total magnetization zero so that the system does not distinguish up and down.It is assumed that the system is very dilute (particle number is very small),the temperature is very low,and the frequency of the harmonic trap is large enough.In these situations,the deviation caused by the neglect of the dipole-dipole interaction and by using the single-mode approximation is reduced.A theoretical calculation beyond the mean field theory is performed and the numerical results are helpful for the evaluation of the unknown strength g 0.

英文摘要：

This paper studies theoretically the spin evolution of a Bose-Einstein condensate starting from a mixture of two or three groups of 52Cr （spin-3） atoms in an optical trap. The initial state is so chosen that the condensate has total magnetization zero so that the system does not distinguish up and down. It is assumed that the system is very dilute （particle number is very small）, the temperature is very low, and the frequency of the harmonic trap is large enough. In these situations, the deviation caused by the neglect of the dipole-dipole interaction and by using the single-mode approximation is reduced. A theoretical calculation beyond the mean field theory is performed and the numerical results are helpful for the evaluation of the unknown strength go.