Darmstadt 2008 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 63: Quantengase (Wechselwirkungseffekte II / Spinorgase)

Q 63.3: Talk

Friday, March 14, 2008, 14:30–14:45, 3G/H

Dipole Oscillations of a Bose-Einstein Condensate in Presence of Defects and Disorder — •Mathias Albert, Nicolas Pavloff, Patricio Leboeuf, and Tobias Paul — Laboratoire de Physique Théorique et Modèles Statistiques, Universite Paris Sud

We study the influence of a weak defect or disorder potential on the dipole modes of a weakly interacting Bose Einstein condensate, confined in a harmonic cigar-shaped trap with a tight transverse confinement but a shallow axial trapping frequency in presence of an external defect or disorder potential. We show that for small-amplitude dipole oscillations the BEC-flow is superfluid and the dipole oscillations are almost undamped, but the external defect potential induces a small shift of the excitation frequency. We compute this frequency shifts by use of a perturbative approach, both in the low-density regime and in the Thomas-Fermi large-density regime and apply this approach -as a first test- to a single Gaussian-shaped barrier potential. Then, we consider the experimental relevant case of an optical speckle-potential where we find uncorrelated frequency shifts of the dipole mode with respect to the pure harmonic case. This behavior is confirmed by numerically solving the Gross-Pitaevskii equation. Finally, we derive a relation between the disorder correlation-function and the ensemble-averaged fluctuations of the frequency shift. This opens the perspective for experiments to obtain from the dipole-frequency fluctuations characteristic parameters of the disorder potential (e.g. correlation lengths).