Countersuperflow instability in miscible two-component Bose-Einstein condensates

TL;DR

This paper theoretically investigates countersuperflow instability in two-component Bose-Einstein condensates, revealing how vortex ring nucleation and turbulence emerge when relative velocities exceed a critical threshold.

Contribution

It introduces a detailed theoretical analysis of countersuperflow instability, vortex nucleation, and turbulence development in two-component BECs, highlighting nonlinear dynamics and vortex interactions.

Findings

Vortex rings nucleate from density patterns during instability.

Rapid vortex ring expansion leads to isotropic turbulence.

Vortex line density scales with the square of relative velocity.

Abstract

We study theoretically the instability of countersuperflow, i.e., two counterpropagating miscible superflows, in uniform two-component Bose-Einstein condensates. Countersuperflow instability causes mutual friction between the superfluids, causing a momentum exchange between the two condensates, when the relative velocity of the counterflow exceeds a critical value. The momentum exchange leads to nucleation of vortex rings from characteristic density patterns due to the nonlinear development of the instability. Expansion of the vortex rings drastically accelerates the momentum exchange, leading to a highly nonlinear regime caused by intervortex interaction and vortex reconnection between the rings. For a sufficiently large interaction between the two components, rapid expansion of the vortex rings causes isotropic turbulence and the global relative motion of the two condensates relaxes. The maximum vortex line density in the turbulence is proportional to the square of the relative velocity.