Driving Bose-Einstein-Condensate vorticity with a rotating normal cloud - art. no. 210403

We have developed an evaporative cooling technique that accelerates the rot ation of an ultracold Rb-87 gas, confined in a static harmonic potential. A s a normal gas is evaporatively spun up and cooled below quantum degeneracy , it is found to nucleate vorticity in a Bose-Einstein condensate. Measurem ents of the condensate's aspect ratio and surface-wave excitations are cons istent with effective rigid-body rotation. Rotation rates of up to 94% of t he centrifugal limit are inferred. A threshold in the normal cloud's rotati on is observed for the intrinsic nucleation of the first vortex. The thresh old value lies below the prediction for a nucleation mechanism involving th e excitation of surface waves of the condensate.