Theory of the Rotating Polaron: Spectrum and Self-Localization

TL;DR

This paper introduces the rotating polaron model, analyzing its spectrum and self-localization properties when a quantum impurity with rotational and translational degrees of freedom interacts with a bosonic bath, relevant for ultracold gases and superfluid helium.

Contribution

It derives the Hamiltonian for the rotating polaron and investigates its spectral properties across different coupling regimes using multiple theoretical methods.

Findings

Internal rotation enhances self-localization of the impurity.

Coupling between linear and angular momenta influences quasiparticle stability.

Spectrum characteristics depend on interaction strength and rotational effects.

Abstract

We study a quantum impurity possessing both translational and internal rotational degrees of freedom interacting with a bosonic bath. Such a system corresponds to a `rotating polaron', which can be used to model, e.g., a rotating molecule immersed in an ultracold Bose gas or superfluid Helium. We derive the Hamiltonian of the rotating polaron and study its spectrum in the weak- and strong-coupling regimes using a combination of variational, diagrammatic, and mean-field approaches. We reveal how the coupling between linear and angular momenta affects stable quasiparticle states, and demonstrate that internal rotation leads to an enhanced self-localization in the translational degrees of freedom.