Ultracold quantum matter

Abstract:

We report the observation of the scissors mode of a Bose-Einstein condensed gas of 87Rb atoms in a magnetic trap, which gives direct evidence of superfluidity in this system. The scissors mode of oscillation is excited by a sudden rotation of the anisotropic trapping potential. For a gas above T(c) (normal fluid) we detect the occurrence of oscillations at two frequencies, with the lower frequency corresponding to the rigid body value of the moment of inertia. Well below T(c) the condensate oscillates at a single frequency, without damping, as expected for a superfluid.

Abstract:

We have measured the time taken for a magnetically trapped cloud of cold cesium atoms in the (F =3,mF=-3) ground state to rethermalize from a nonequilibrium spatial and velocity distribution. From these measurements we infer the dependences of the elastic scattering cross section on temperature and magnetic field in the ranges 1 - 30 μΚ and 0.05-2.0 mT, respectively. We determine a lower bound on the magnitude of the (3,-3) + (3,-3) s-wave scattering length of 940a0.

Abstract:

We describe the construction and operation of a time-orbiting potential trap that has different oscillation frequencies along its three principal axes. These axes can be rotated and we have observed Bose-Einstein condensates of 87Rb with a rotating ellipsoidal shape. Under these conditions it has been predicted that quantized vortices form and are stable.