Manifestation of superfluidity in atom-number-imbalanced two-component Bose-Einstein condensates

Abstract

Superfluid and dissipative regimes in the dynamics of a two-component quasi-one-dimensional Bose-Einstein condensate (BEC) with unequal atom numbers in the components have been explored. The system supports localized waves of the symbiotic type owing to the same-species repulsion and cross-species attraction. The minority BEC component moves through the majority component and creates excitations. To quantify the emerging excitations we introduce a time-dependent function called disturbance. Through numerical simulations of the coupled Gross-Pitaevskii equations with periodic boundary conditions, we have revealed a critical velocity of the localized wave, above which a transition from superfluid to dissipative regime occurs, evidenced by a sharp increase in the disturbance function. The factors responsible for the discrepancy between the actual critical velocity and the speed of sound, expected from theoretical arguments, have been discussed.

11 pages, 4 figures. Submitted to a special issue of the journal Symmetry: "Nonlinear Science and Numerical Simulation with Symmetry"