Charged polarons and molecules in a Bose-Einstein Condensate

TL;DR

This paper explores the formation and properties of charged polarons and molecules in a Bose-Einstein condensate using theoretical models, revealing multiple bound states and their spectral characteristics.

Contribution

It introduces a comprehensive theoretical framework for understanding charged polarons and molecular ions in BECs, including spectral analysis and dynamical behavior.

Findings

Multiple spectral branches indicating bound states

Spectral weight scales with number of bound atoms

Dynamics show regimes of quasiparticle propagation and decay

Abstract

We investigate the properties a mobile ion immersed in a Bose-Einstein condensate (BEC) using different theoretical approaches. A coherent state variational ansatz predicts that the ion spectral function exhibits several branches in addition to polaronic quasiparticle states, and we employ a diagrammatic analysis of the ion-atom scattering in the BEC to identify them as arising from the binding of an increasing number of bosons to the ion. We develop a simplified model describing the formation of these molecular ions showing that their spectral weight scales with the number of bound atoms. The number of atoms in the dressing cloud around the ion are calculated from thermodynamic arguments, and we finally show that the dynamics ensuing the injection of an ion into the BEC exhibits various regimes governed by coherent quasiparticle propagation and decay.