We study a rapidly rotating Bose-Einstein condensate in anharmonic confinement and find that many properties, such as the critical rotating frequency and phase diagram, are different from those in a harmonic trap. We investigate the phase transitions between various vortex lattices and find that a hole emerges in the center of the cloud when the rotating frequency Θ reaches Θh but it becomes invisible when Θ > 1.0842ω ⊥.
 E. Hodby, G. Hechenblaikner, S.A. Hopkins, O.M. Maraggraveo and C.J. Foot: “Vortex Nucleation in Bose-Einstein Condensates in an Oblate, Purely Magnetic Potential”, Phys. Rev. Lett., Vol. 88, (2002), art. 010405.
 P.C. Haljan, I. Coddington, P. Engels and E.A. Cornell: “Driving Bose-Einstein-Condensate Vorticity with a Rotating Normal Cloud”, Phys. Rev. Lett., Vol. 87, (2001), art. 210403.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.