Fragmented Condensate Ground State of Trapped Weakly Interacting Bosons   in Two Dimensions
  The ground state and its structure for a rotating, harmonically trapped N-Boson system with a weak repulsive contact interaction are studied as the angular momentum L increases up to 3N. We show that the ground state is generally a fragmented condensate due to angular momentum conservation. In response to an (arbitrarily weak) asymmetric perturbation of the trap, however, the fragmented ground state can be transformed into a single condensate state. We manifest this intrinsic instability by calculating the conditional probability distributions, which show patterns analogous to the boson density distributions predicted by mean-field theory. 
Xia-Ji Liu, Hui Hu, Lee Chang, Weiping Zhang, Shi-Qun Li, and Yu-Zhu   Wang