Multi-impurity polarons in a dilute Bose-Einstein condensate

TL;DR

This paper investigates how multiple impurity atoms in a dilute Bose-Einstein condensate can self-localize and induce phase separation, revealing new collective behaviors of impurities in quantum fluids.

Contribution

It introduces the concept of co-self-localization of multiple impurities and explores conditions for phase separation and stable impurity liquids in BECs.

Findings

Multiple impurities can self-localize at lower interaction strengths than single impurities.

Co-self-localization acts as a nucleation process for phase separation.

Impurity-impurity repulsion can stabilize a liquid of impurity polarons.

Abstract

We describe the ground state of a large, dilute, neutral atom Bose- Einstein condensate (BEC) doped with N strongly coupled mutually indistinguishable, bosonic neutral atoms (referred to as "impurity") in the polaron regime where the BEC density response to the impurity atoms remains significantly smaller than the average density of the surrounding BEC. We find that N impurity atoms (N is not one) can self-localize at a lower value of the impurity-boson interaction strength than a single impurity atom. When the 'bare' short-range impurity-impurity repulsion does not play a significant role, the self-localization of multiple bosonic impurity atoms into the same single particle orbital (which we call co-self-localization) is the nucleation process of the phase separation transition. When the short-range impurity-impurity repulsion successfully competes with co-self-localization, the system may form a stable liquid of self-localized single impurity polarons.