title: Direct observation of irrotational flow and evidence of superfluidity in a rotating Bose-Einstein condensate.
abstract: We have observed the expansion of vortex-free, rotating Bose condensates after their sudden release from a slowly rotating anisotropic trap. Conservation of angular momentum, combined with the constraint of irrotational flow, cause the rotating condensate to expand in a distinctively different way to one released from a static (nonrotating) trap. This difference provides clear experimental evidence of the purely irrotational velocity field associated with a superfluid. We observed this behavior in absorption images taken along the rotation axis.
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Hechenblaikner
authors.forename: E
authors.initials: E
authors.lastname: Hodby
authors.forename: S A
authors.initials: SA
authors.lastname: Hopkins
authors.forename: O M
authors.initials: OM
authors.lastname: Maragò
authors.forename: C J
authors.initials: CJ
authors.lastname: Foot