Inducing spin-order with an impurity: phase diagram of the magnetic Bose polaron

TL;DR

This paper explores the phase diagram and properties of magnetic Bose polarons in a one-dimensional spinor Bose gas, revealing how impurities induce spin-order and self-localization, with implications for quantum control in cold atom systems.

Contribution

It introduces a detailed phase diagram of magnetic Bose polarons, highlighting impurity-induced spin-ordering and the limitations of mean-field theory near immiscibility.

Findings

Impurities can induce self-localized magnetic polarons with strong impurity-spin dressing.

The phase diagram includes attractive, repulsive, and phase-separation regimes.

Impurities can control spin polarization and generate spin-spin correlations.

Abstract

We investigate the formation of magnetic Bose polaron, an impurity atom dressed by spin-wave excitations, in a one-dimensional spinor Bose gas. In terms of an effective potential model the impurity is strongly confined by the host excitations which can even overcome the impurity-medium repulsion leading to a self-localized quasi-particle state. The phase diagram of the attractive and self-bound repulsive magnetic polaron, repulsive non-magnetic (Fr{\" o}hlich-type) polaron and impurity-medium phase-separation regimes is explored with respect to the Rabi-coupling between the spin components, spin-spin interactions and impurity-medium coupling. The residue of such magnetic polarons decreases substantially in both strong attractive and repulsive branches with strong impurity-spin interactions, illustrating significant dressing of the impurity. The impurity can be used to probe and maneuver the spin polarization of the magnetic medium while suppressing ferromagnetic spin-spin correlations. It is shown that mean-field theory fails as the spinor gas approaches immiscibility since the generated spin-wave excitations are prominent. Our findings illustrate that impurities can be utilized to generate controllable spin-spin correlations and magnetic polaron states which can be realized with current cold atom setups.