Single impurities in a Bose-Einstein condensate can make two polaron flavors

TL;DR

This paper demonstrates that impurities in Bose-Einstein condensates can self-localize into two distinct polaron states, with a smooth transition between them, characterized by just two key parameters.

Contribution

It reveals that dilute BECs can host two different impurity polaron states and provides a framework to smoothly transition between these states using two dimensionless couplings.

Findings

Impurities can form Landau-Pekar and bubble polarons in BECs.

The system is characterized by two key dimensionless coupling constants.

A smooth crossover between the two polaron states is possible.

Abstract

Polarons, self-localized composite objects formed by the interaction of a single impurity particle with a host medium, are a paradigm of strong interaction many-body physics. We show that dilute gas Bose-Einstein condensates (BEC's) are the first medium known to self-localize the same impurity particles both in a Landau-Pekar polaron state akin to that of self-localized electrons in a dielectric lattice, and in a bubble state akin to that of electron bubbles in helium. We also show that the BEC-impurity system is fully characterized by just two dimensionless coupling constants, and that it can be adiabatically steered from the Landau-Pekar regime to the bubble regime in a smooth crossover trajectory.