Behaviour of Rotating Bose--Einstein Condensates Under Shrinking

When the repulsive interaction strength between atoms decreases, the size of a rotating Bose--Einstein condensate will consequently shrink. We find that the rotational frequency will increase during the shrinking of condensate, which is a quantum mechanical analogy to ballet dancing. Compared to a non-rotating condensate, the size of a rotating BEC will eventually be saturated at a finite value when the interaction strength is gradually reduced. We also calculate the vortex dynamics induced by the atomic current, and discuss the difference of vortex dynamics in this case and that observed in a recent experiment carried out by the JILA group Phys. Rev. Lett. 90(2003)170405.