Rabi-coupled Countersuperflow in Binary Bose-Einstein Condensates

TL;DR

This paper theoretically investigates how Rabi coupling stabilizes periodic density patterns and soliton arrays in binary Bose-Einstein condensates, analyzing their properties, transformations, and stability conditions.

Contribution

It introduces a theoretical framework for understanding Rabi-coupled countersuperflow patterns, including soliton formation and stability analysis in binary BECs.

Findings

Periodic density patterns are stabilized by Rabi coupling.

Soliton solutions are characterized by width and density depression.

Patterns transform from soliton arrays to sinusoidal as period decreases.

Abstract

We show theoretically that periodic density patterns are stabilized in two counter-propagating Bose-Einstein condensates of atoms in different hyperfine states under Rabi coupling. In the presence of coupling, the relative velocity between two components is localized around density depressions in quasi-one-dimensional systems. When the relative velocity is sufficiently small, the periodic pattern reduces to a periodic array of topological solitons as kinks of relative phase. According to our variational and numerical analyses, the soliton solution is well characterized by the soliton width and density depression. We demonstrate the dependence of the depression and width on the Rabi frequency and the coupling constant of inter-component density-density interactions. The periodic pattern of the relative phase transforms continuously from a soliton array to a sinusoidal pattern as the period becomes smaller than the soliton width. These patterns become unstable when the localized relative velocity exceeds a critical value. The stability-phase diagram of this system is evaluated with a stability analysis of countersuperflow, by taking into account the finite-size-effect owing to the density depression.