Rapidly rotating Bose-Einstein condensates in anharmonic potentials

Rapidly rotating Bose-Einstein condensates confined in anharmonic traps can exhibit a rich variety of vortex phases, including a vortex lattice, a vortex lattice with a hole, and a giant vortex. Using an augmented Thomas - Fermi variational approach to determine the ground state of the condensate in the rotating frame - valid for sufficiently strongly interacting condensates - we determine the transitions between these three phases for a quadratic- plus- quartic confining potential. Combining the present results with previous numerical simulations of small rotating condensates in such anharmonic potentials, we delineate the general structure of the zero-temperature phase diagram.