Browsing by Author "Dries, D."

Now showing 1 - 5 of 5
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    Collective excitation of a Bose-Einstein condensate by modulation of the atomic scattering length
    (American Physical Society, 2010) Pollack, S.E.; Dries, D.; Hulet, R.G.; Magalhães, K.M.F.; Henn, E.A.L.; Ramos, E.R.F.; Caracanhas, M.A.; Bagnato, V.S.; Rice Quantum Institute
    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.
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    Dissipative transport of a Bose-Einstein condensate
    (American Physical Society, 2010) Dries, D.; Pollack, S.E.; Hitchcock, J.M.; Hulet, R.G.; Rice Quantum Institute
    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 Li7 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.
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    Extreme Tunability of Interactions in a Li7 Bose-Einstein Condensate
    (American Physical Society, 2009) Pollack, S.E.; Dries, D.; Junker, M.; Chen, Y.P.; Corcovilos, T.A.; Hulet, R.G.; Rice Quantum Institute
    We use a Feshbach resonance to tune the scattering length a of a Bose-Einstein condensate of Li7 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.
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    Phase coherence and superfluid-insulator transition in a disordered Bose-Einstein condensate
    (American Physical Society, 2008) Chen, Yong P.; Hitchcock, J.; Dries, D.; Junker, M.; Welford, C.; Hulet, R.G.; Rice Quantum Institute; Richard E. Smalley Institute for Nanoscale Science and Technology
    We have studied the effects of a disordered optical potential on the transport and phase coherence of a Bose-Einstein condensate (BEC) of L7i atoms. At moderate disorder strengths (VD), we observe inhibited transport and damping of dipole excitations, while in time-of-flight images, random but reproducible interference patterns are observed. In situ images reveal that the appearance of interference is correlated with density modulation, without complete fragmentation. At higher VD, the interference contrast diminishes as the BEC fragments into multiple pieces with little phase coherence.
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    Photoassociation of a Bose-Einstein Condensate near a Feshbach Resonance
    (American Physical Society, 2008) Junker, M.; Dries, D.; Welford, C.; Hitchcock, J.; Chen, Y.P.; Hulet, R.G.; Rice Quantum Institute
    We measure the effect of a magnetic Feshbach resonance (FR) on the rate and light-induced frequency shift of a photoassociation resonance in ultracold Li7. The photoassociation-induced loss-rate coefficient Kp depends strongly on magnetic field, varying by more than a factor of 10?4 for fields near the FR. At sufficiently high laser intensities, Kp for a thermal gas decreases with increasing intensity, while saturation is observed for the first time in a Bose-Einstein condensate. The frequency shift is also strongly field dependent and exhibits an anomalous blueshift for fields just below the FR.