Physical Review A

Perturbing a persistent current with an external potential

Juha Javanainen, Yi Zheng

Published May 16, 2001• 6 citations

Abstract

We consider the changes in the spectrum of elementary excitations of a flowing superfluid that result when a weak external perturbing potential is added. As a specific application, we study the critical velocity of superfluid flow in a slightly distorted, tight, toroidal trap for atoms. The critical velocity is not accurately predicted by the argument that the flow turns dissipative when the local flow velocity exceeds the local speed of sound somewhere in the fluid. The unusual critical velocity probably reflects the essentially one-dimensional physics of the model.

DOI: 10.1103/physreva.63.063610

Related papers

Persistent currents in a toroidal trap

Juha Javanainen, Sun Mok Paik, Sung Mi Yoo

Using elementary microscopic methods, we theoretically study persistent flow of an alkali-metal vapor Bose-Einstein condensate around a tight toroidal trap. The angular velocity of a persistent current must be smaller than the angular frequency of the lowest condensate excitation. A supercurrent may be excited by rotating a perturbing potential that is strong enough to cut the toroidal condensate.

Physical Review AJul 1, 199836 citations

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

Gentaro Watanabe A, F. Dalfovo, Francesco Piazza +2 more

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.

arXiv:0907.0621Physical Review ANov 3, 200954 citations

Superfluid flow above the critical velocity

Asaf Paris-Mandoki, J. Shearring, Francesco Mancarella +3 more

Superfluidity and superconductivity have been widely studied since the last century in many different contexts ranging from nuclear matter to atomic quantum gases. The rigidity of these systems with respect to external perturbations results in frictionless motion for superfluids and resistance-free electric current flow in superconductors. This peculiar behaviour is lost when external perturbations overcome a critical threshold, i.e. above a critical magnetic field or a critical current for superconductors. In superfluids, such as liquid helium or ultracold gases, the corresponding quantities are a critical rotation rate and a critical velocity respectively. Enhancing the critical values is of great fundamental and practical value. Here we demonstrate that superfluidity can be completely restored for specific, arbitrarily large flow velocities above the critical velocity through quantum interference-induced resonances providing a nonlinear counterpart of the Ramsauer-Townsend effect occurring in ordinary quantum mechanics. We illustrate the robustness of this phenomenon through a thorough analysis in one dimension and prove its generality by showing the persistence of the effect in non-trivial 2d systems. This has far reaching consequences for the fundamental understanding of superfluidity and superconductivity and opens up new application possibilities in quantum metrology, e.g. in rotation sensing.

arXiv:1505.00358Scientific ReportsAug 16, 201713 citations

Decay of a superfluid current of ultracold atoms in a toroidal trap

Amy C. Mathey, Charles W. Clark, Ludwig Mathey

Using a numerical implementation of the truncated Wigner approximation, we simulate the experiment reported by Ramanathan et al. in Phys. Rev. Lett. 106, 130401 (2011), in which a Bose-Einstein condensate is created in a toroidal trap and set into rotation via a phase imprinting technique. A potential barrier is then placed in the trap to study the decay of the superflow. We find that the current decays via thermally activated phase slips, which can also be visualized as vortices crossing the barrier region in the radial direction. Adopting the notion of critical velocity used in the experiment, we determine it to be lower than the local speed of sound at the barrier, in contradiction to the predictions of the zero-temperature Gross-Pitaevskii equation. We map out the superfluid decay rate and critical velocity as a function of temperature and observe a strong dependence. Thermal fluctuations offer a partial explanation of the experimentally observed reduction of the critical velocity from the phonon velocity.

arXiv:1207.0501Physical Review AAug 4, 201449 citations

Finding the breaking point

Jelena Stajic

Quantum Gases A superfluid can flow without viscosity but only if the speed of the flow is lower than the so-called critical velocity. Sobirey et al. measured the critical velocity of a system of ultracold fermionic atoms confined to two dimensions. The researchers trapped a gas of lithium-6 atoms in a box-shaped potential and then moved another, periodic potential through the trap. The response of the gas to this perturbation showed a sudden increase when the speed of the periodic potential reached the critical velocity. Science , abc8793, this issue p. [844][1] [1]: /lookup/doi/10.1126/science.abc8793

ScienceMay 20, 20210 citations

Observation of superfluidity in a strongly correlated two-dimensional Fermi gas

Lennart Sobirey, Niclas Luick, Markus Bohlen +3 more

Finding the breaking point A superfluid can flow without viscosity but only if the speed of the flow is lower than the so-called critical velocity. Sobirey et al. measured the critical velocity of a system of ultracold fermionic atoms confined to two dimensions. The researchers trapped a gas of lithium-6 atoms in a box-shaped potential and then moved another, periodic potential through the trap. The response of the gas to this perturbation showed a sudden increase when the speed of the periodic potential reached the critical velocity. Science , abc8793, this issue p. 844

arXiv:2005.07607ScienceMay 21, 202152 citations