D. Dries

Extreme Tunability of Interactions in a 7Li Bose-Einstein Condensate

We use a Feshbach resonance to tune the scattering length a of a Bose-Einstein condensate of 7Li in the |F=1,mF=1> state. Using the spatial extent of the trapped condensate, we extract a over a range spanning 7 decades from small attractive interactions to extremely strong repulsive interactions. The shallow zero crossing in the wing of the Feshbach resonance enables the determination of a as small as 0.01 Bohr radii. Evidence of the weak anisotropic magnetic dipole interaction is obtained by comparison with different trap geometries for small a.

Collective excitation of a Bose-Einstein condensate by modulation of the atomic scattering length

We excite the lowest-lying quadrupole mode of a Bose-Einstein condensate by modulating the atomic scattering length via a Feshbach resonance. Excitation occurs at various modulation frequencies, and resonances located at the natural quadrupole frequency of the condensate and at the first harmonic are observed. We also investigate the amplitude of the excited mode as a function of modulation depth. Numerical simulations based on a variational calculation agree with our experimental results and provide insight into the observed behavior.

Dissipative transport of a Bose-Einstein condensate

We investigate the effects of impurities, either correlated disorder or a single Gaussian defect, on the collective dipole motion of a Bose-Einstein condensate of {sup 7}Li in an optical trap. We find that this motion is damped at a rate dependent on the impurity strength, condensate center-of-mass velocity, and interatomic interactions. Damping in the Thomas-Fermi regime depends universally on the disordered potential strength scaled to the condensate chemical potential and the condensate velocity scaled to the speed of sound. The damping rate is comparatively small in the weakly interacting regime, and, in this case, is accompanied by strong condensate fragmentation. In situ and time-of-flight images of the atomic cloud provide evidence that this fragmentation is driven by dark soliton formation.