Collective Modes of Mutually-Attractive Coupled Superfluids

Collective modes of atomic Bose-Einstein condensates have been well investigated in condensates with repulsive interactions [1], across the miscibility-immiscibility boundary [2], and in dual Bose-Fermi superfluids [3]. Here we present a detailed study of Bose-Bose mixture collective dynamics in the presence of attractive interspecies interactions: specifically, we consider a Cs-Yb(174) mixture displaced from its equilibrium position under realistic experimental conditions [4], and demonstrate the distinct excitation mechanisms (single-component excitations, counterflow instabilities) and the evolving nature of the rich dynamical mode coupling. Our findings, supported by both mean-field dynamics and detailed characterization of the mixture’s quasiparticle (Bogoliubov) excitation spectrum, reveal the emergence of beating, associated with a small splitting of the natural oscillation frequency of the dominant component due to induced coupled co-moving and counter-moving modes. Such dynamics is characterized in terms of damping rates, dependence on atom number ratio, and initial kick strength, further analyzing the co-moving and counter-moving coupled modes in terms of both attractive and repulsive interactions.

[1] G. Modugno et al., PRL 89, 190404 (2002).

[2] K.L. Lee et al., PRA 94, 013602 (2016).

[3] I. Ferrier-Barbut et al., Sceicne 345, 1035 (2014).

[4] K.E. Wilson et al., arXiv:2012.11008

[5] I.K. Liu et al. (in preparation)