Counterflow dynamics of two correlated impurities immersed in a bosonic gas

TL;DR

This paper investigates the static and dynamic behaviors of two correlated impurities in a one-dimensional bosonic medium, revealing various bound states and collision dynamics influenced by interactions and confinement, with implications for cold atom experiments.

Contribution

It provides a comprehensive analysis of impurity correlations, phase diagrams, and dynamical responses in different trapping geometries, highlighting new bound states and interaction effects.

Findings

Identification of bipolaron-like bound impurity states for strong attraction.

Impurity localization in a box trap due to induced interactions.

Periodic collision and expansion dynamics in harmonic traps.

Abstract

The counterflow dynamics of two correlated impurities in a double-well coupled to an one-dimensional bosonic medium is explored. We determine the ground state phase diagram of the system according to the impurity-medium entanglement and the impurities two-body correlations. Specifically, bound impurity structures reminiscent of bipolarons for strong attractive couplings as well as configurations with two clustered or separated impurities in the repulsive case are identified. The interval of existence of these phases depends strongly on the impurity-impurity interactions and external confinement of the medium. Accordingly the impurities dynamical response, triggered by suddenly ramping down the central potential barrier, is affected by the medium's trapping geometry. In particular, for a box-confined medium repulsive impurity-medium couplings lead, due to attractive induced interactions, to the localization of the impurities around the trap center. In contrast, for a harmonically trapped medium the impurities perform a periodic collision and expansion dynamics further interpreted in terms of a two-body effective model. Our findings elucidate the correlation aspects of the collisional physics of impurities which should be accessible in recent cold atom experiments.