Bosons in a toroidal trap: Ground state and vortices

We study the Bose-Einstein condensate (BEC) in a 3-D toroidal Mexican hat trap. By changing the parameters of the potential, or the number of bosons, it is possible to modify strongly the density profile of the BEC. We consider the ground state properties for positive and negative scattering length and calculate the spectrum elementary excitations. We also discuss the macroscopic phase coherence and superfluidity of the BEC by analyzing vortex...