title: Driving Bose-Einstein-condensate vorticity with a rotating normal cloud.
abstract: We have developed an evaporative cooling technique that accelerates the rotation of an ultracold 87Rb gas, confined in a static harmonic potential. As a normal gas is evaporatively spun up and cooled below quantum degeneracy, it is found to nucleate vorticity in a Bose-Einstein condensate. Measurements of the condensate's aspect ratio and surface-wave excitations are consistent with effective rigid-body rotation. Rotation rates of up to 94% of the centrifugal limit are inferred. A threshold in the normal cloud's rotation is observed for the intrinsic nucleation of the first vortex. The threshold value lies below the prediction for a nucleation mechanism involving the excitation of surface waves of the condensate.
authors.affiliation: JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA.
authors.forename: P C
authors.initials: PC
authors.lastname: Haljan
authors.forename: I
authors.initials: I
authors.lastname: Coddington
authors.forename: P
authors.initials: P
authors.lastname: Engels
authors.forename: E A
authors.initials: EA
authors.lastname: Cornell