Instabilities of a matter wave in a matter grating

TL;DR

This paper studies the stability of Bose-Einstein condensates in a coupled matter wave system, revealing complex instability regimes due to inter-species phonon interactions and contrasting with single-condensate scenarios.

Contribution

It introduces a detailed analysis of dynamical instabilities in a two-condensate system within a matter grating, highlighting the effects of inter-species coupling.

Findings

Rich structure of dynamical instability regimes identified

Inter-species phonon coupling significantly alters stability

Analytic limit explains the basic structure of instability diagrams

Abstract

We investigate the stability of Bloch waves for a Bose-Einstein condensate moving through a periodic lattice created by another condensate modulated by an optical lattice. We show that the coupling of phonon-antiphonon modes of the two species give rise to a very rich structure of the regimes for dynamical instability, with significant differences with respect to the case of a single condensate in an optical lattice. We characterize the relative weight of each condensate in the mixing and discuss an analytic limit that accounts for the bare structure of the instability diagrams.