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

TL;DR

This paper investigates superfluidity in two-component Bose-Einstein condensates with unequal atom numbers, identifying a critical velocity for transition from superfluid to dissipative behavior through numerical simulations.

Contribution

It introduces the disturbance function to quantify excitations and reveals the critical velocity for superfluidity breakdown in atom-number-imbalanced BECs.

Findings

Identification of a critical velocity for superfluid to dissipative transition

Introduction of the disturbance function to measure excitations

Discussion of factors causing discrepancy with theoretical speed of sound

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.