Rotational spectra of weakly interacting Bose-Einstein condensates
  We study the spectrum of rotating Bose-Einstein Condensates in the limit of weak repulsive interactions and present analytical and numerical results for energies and wave functions. While the low-lying states are of collective nature, the high-lying states are dominated by single-particle excitations and can accurately approximated by simple polynomial expressions. In the limit that the number of particles is large compared to the number of excited quanta, the single-particle states become excellent approximations to the eigenstates, and a rather simple ordering scheme is obtained. 
Thomas Papenbrock and George F. Bertsch (Institute for Nuclear Theory,   Seattle, USA)