Ultra-Dilute Gas of Polarons in a Bose-Einstein Condensate

We investigate the properties of a dilute gas of impurities embedded in an ultracold gas of bosons that forms a Bose-Einstein condensate (BEC). This work focuses mainly on the equation of state (EoS) of the impurity gas at zero temperature and the induced interaction between impurities mediated by the host bath. We use perturbative field-theory approaches, such as Hugenholtz-Pines formalism, in the weakly interacting regime. In turn, for strong interactions, we aim at non-perturbative techniques such as quantum-Monte Carlo (QMC) methods. Our findings agree with experimental observations for an ultra dilute gas of impurities, modeled in the framework of the single impurity problem; however, as the density of impurities increases, systematic deviations are displayed with respect to the one-body Bose polaron problem.

Automated summary

This study investigates the properties of a dilute gas of impurities embedded in an ultracold gas of bosons that forms a Bose-Einstein condensate. The focus is on the equation of state of the impurity gas at zero temperature and the interaction between impurities mediated by the host bath. Perturbative field-theory approaches and non-perturbative techniques are used for weak and strong interactions, respectively. The findings agree with experimental observations for an ultra dilute gas of impurities, but systematic deviations are observed as the density of impurities increases compared to the one-body Bose polaron problem.