Critical velocity of superfluid flow through single-barrier and periodic potentials

Year: 2009

Authors: Watanabe G., Dalfovo F., Piazza F., Pitaevskii L.P., Stringari S.

Autors Affiliation: Univ Trent, CNR, INFM BEC, I-38050 Trento, Italy; Univ Trent, Dept Phys, I-38050 Trento, Italy; RIKEN, Wako, Saitama 3510198, Japan; Kapitza Inst Phys Problems, Moscow 119334, Russia

Abstract: We investigate the problem of an ultracold atomic gas in the superfluid phase flowing in the presence of a potential barrier or a periodic potential. We use a hydrodynamic scheme in the local density approximation (LDA) to obtain an analytic expression for the critical current as a function of the barrier height or the lattice intensity, which applies to both Bose and Fermi superfluids. In this scheme, the stationary flow becomes energetically unstable when the local superfluid velocity is equal to the local sound velocity at the point where the external potential is maximum. We compare this prediction with the results of the numerical solutions of the Gross-Pitaevskii and Bogoliubov-de Gennes equations. We discuss the role of long-wavelength excitations in determining the critical velocity. Our results allow one to identify the different regimes of superfluid flow, namely, the LDA hydrodynamic regime, the regime of quantum effects beyond LDA for weak barriers and the regime of tunneling between weakly coupled superfluids for strong barriers. We finally discuss the relevance of these results in the context of current experiments with ultracold gases.

Journal/Review: PHYSICAL REVIEW A

Volume: 80 (5)      Pages from: 053602  to: 053602

More Information: We acknowledge M. Modugno and A. Smerzi for fruitful discussions and for suggestions about the numerical techniques. Calculations were performed on the HPC facilities WIGLAF at the University of Trento, BEN at ECT* in Trento, and RIKEN Super Combined Cluster System. This work, as a part of the European Science Foundation EUROCORES Program EuroQUAM-FerMix, was supported by funds from the CNR and the EC Sixth Framework Programme. It is also supported by MiUR.
KeyWords: Bose-Einstein condensation; density functional theory; fermion systems; hydrodynamics; optical lattices
DOI: 10.1103/PhysRevA.80.053602

Citations: 46
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