Shape deformations and angular-momentum transfer in trapped Bose-Einstein condensates - art. no. 011601

Angular momentum can be transferred to a trapped Bose-Einstein condensate b y distorting its shape with an external rotating field, provided the rotati onal frequency is larger than a critical frequency fixed by the energy and angular momentum of the excited states of the system. By using the Gross-Pi taevskii equation and sum rules, we explore the dependence of such a critic al frequency on the multipolarity of the excitations and the asymmetry of t he confining potential. We also discuss its possible relevance for vortex n ucleation in rotating traps.