The critical velocity in the BEC-BCS crossover

Abstract

We map out the critical velocity in the crossover from Bose-Einstein condensation (BEC) to Bardeen-Cooper-Schrieffer superfluidity with ultracold ${}^6$Li gases. A small attractive potential is dragged along lines of constant column density. The rate of the induced heating increases steeply above a critical velocity $v_c$. In the same samples, we measure the speed of sound $v_s$ by exciting density waves and compare the results to the measured values of $v_c$. We perform numerical simulations in the BEC regime and find very good agreement, validating the approach. In the strongly correlated regime, where theoretical predictions only exist for the speed of sound, our measurements of $v_c$ provide a testing ground for theoretical approaches.

5 pages, 3 figures

References in corpus (14)

• Many-Body Physics with Ultracold Gases
• Theory of ultracold Fermi gases
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• Strong saturation absorption imaging of dense clouds of ultracold atoms
• Superfluid behaviour of a two-dimensional Bose gas
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• Critical velocity for superfluid flow across the BEC-BCS crossover
• Polarization Measurements and the Pairing Gap in the Universal Regime
• High-resolution imaging of ultracold fermions in microscopically tailored optical potentials
• Sound propagation in elongated superfluid fermion clouds
• Critical velocity of superfluid flow through single barrier and periodic potentials
• First and second sound in cylindrically trapped gases
• Effects of periodic potentials on the critical velocity of superfluid Fermi gases in the BCS-BEC crossover
• Stability of superfluid Fermi gases in optical lattices

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