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arXiv:1402.6086 · Journal of Physics B Atomic Molecular and Optical Physics

Persistent currents in a two-component Bose–Einstein condensate confined in a ring potential

J Smyrnakis, M Magiropoulos, Nikolaos K. Efremidis, G. M. Kavoulakis

Published Oct 15, 2014• 8 citations
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Abstract

We present variational and numerical solutions for the problem of stability of persistent currents in a two-component Bose–Einstein condensate of distinguishable atoms which rotate in a ring potential. We consider the general class of solutions of constant density in the two components separately, thus providing an alternative approach to the solution of the same problem given recently by Wu and Zaremba (2013 Phys. Rev. A 88 063640 ). Our approach provides a physically transparent solution for this delicate problem. Finally, we give a unified and simple picture of the lowest energy state of the system for large values of the coupling.

DOI
10.1088/0953-4075/47/21/215302

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We present variational and numerical solutions for the problem of stability of persistent currents in a two-component Bose–Einstein condensate of distinguishable atoms which rotate in a ring potential. We consider the general class of solutions of constant density in the two components separately, thus providing an alternative approach to the solution of the same problem given recently by Wu and Zaremba (2013 Phys. Rev. A 88 063640 ). Our approach provides a physically transparent solution for this delicate problem. Finally, we give a unified and simple picture of the lowest energy state of the system for large values of the coupling.
We study the stability of persistent currents in a coherently coupled quasi-two-dimensional Bose-Einstein condensate confined in a ring trap at T=0T=0T=0. By numerically solving Gross-Pitaevskii equations and by analyzing the excitation spectrum obtained from diagonalization of the Bogoliubov--de Gennes matrix, we describe the mechanisms responsible for the decay of the persistent currents depending on the values of the interaction coupling constants and the Rabi frequency. When the unpolarized system decays due to an energetic instability in the density channel, the spectrum may develop a rotonlike minimum, which gives rise to the finite wavelength excitation necessary for vortex nucleation at the inner surface. When decay in the unpolarized system is driven by spin-density excitations, the finite wavelength naturally arises from the existence of a gap in the excitation spectrum. In the polarized phase of the coherently coupled condensate, there is a hybridization of the excitation modes that leads to complex decay dynamics. In particular, close to the phase transition, a state of broken rotational symmetry is found to be stationary and stable.
Motivated by a recent experiment [Beattie, Moulder, Fletcher, and Hadzibabic, Phys. Rev. Lett. 110, 025301 (2013)], we study the superflow of atomic spinor Bose-Einstein condensates optically trapped in a ring-shaped geometry. Within a dissipative mean-field approach we simulate a two-component condensate in conditions adapted to the experiment. In qualitative agreement with the experimental findings, we observe stable superflow if the spin-population imbalance is above some well-defined threshold value. Below the stability threshold the persistent currents with higher-order circulation decay in quantized steps, and the vortex lines escape from the center of the ring through dynamically created ``weak links'' in the condensate annulus. These regions with reduced density of one spin component are filled by atoms of the other component. The vortices then leave the ring-shaped high-density region of the condensate and finally decay into elementary excitations.
Abstract We consider a Bose–Einstein condensate, which is confined in a very tight toroidal/annular trap, in the presence of a potential, which breaks the axial symmetry of the Hamiltonian. We investigate the stationary states of the condensate, when its density distribution co-rotates with the symmetry-breaking potential. As the strength of the potential increases, we have a gradual transition from vortex excitation to solid-body-like motion. Of particular importance are states where the system is static and yet it has a nonzero current/circulation, which is a realization of persistent currents/reflectionless potentials.