Dark-dark solitons and modulational instability in miscible, two-component Bose-Einstein condensates

TL;DR

This paper studies the emergence of dark-dark solitons and modulational instability in two-component Bose-Einstein condensates under counterflow, combining experimental observations with numerical simulations.

Contribution

It reports the first experimental observation of dark-dark vector solitons in BECs and analyzes their dynamics and instabilities.

Findings

Modulational instability leads to dark-dark soliton formation.

Dark-dark solitons exhibit beating dynamics.

Transverse instability can cause vortex line structures.

Abstract

We investigate the dynamics of two miscible superfluids experiencing fast counterflow in a narrow channel. The superfluids are formed by two distinguishable components of a trapped dilute-gas Bose-Einstein condensate (BEC). The onset of counterflow-induced modulational instability throughout the cloud is observed and shown to lead to the proliferation of dark-dark vector solitons. These solitons, which we observe for the first time in a BEC, do not exist in single-component systems, exhibit intriguing beating dynamics and can experience a transverse instability leading to vortex line structures. Experimental results and multi-dimensional numerical simulations are presented.