Vortex stabilization in a small rotating asymmetric Bose-Einstein condensate - art. no. 023602

We use a variational method to investigate the ground-state phase diagram o f a small, asymmetric Bose-Einstein condensate with respect to the dimensio nless interparticle interaction strength gamma and the applied external rot ation speed Omega. For a given gamma, the transition lines between no-vorte x and vortex states are shifted toward higher Omega relative to those for t he symmetric case. We also find a re-entrant behavior, where the number of vortex cores can decrease for large Omega. In addition, stabilizing a vorte x in a rotating asymmetric trap requires a minimum interaction strength. Fo r a given asymmetry, the evolution of the variational parameters with incre asing Omega shows two different types of transitions (sharp or continuous), depending on the strength of the interaction. We also investigate transiti ons to states with higher vorticity; the corresponding angular momentum inc reases continuously as a function of Omega.