Polaron Problems in Ultracold Atoms: Role of a Fermi Sea across Different Spatial Dimensions and Quantum Fluctuations of a Bose Medium

TL;DR

This paper explores polaron phenomena in ultracold atoms, examining how impurities affect Fermi and Bose media across different dimensions and temperatures, revealing insights into spectral functions and condensate depletion.

Contribution

It introduces a finite-temperature diagrammatic approach for Fermi polarons and analyzes medium modifications and spectral functions across dimensions, also studying Bose condensate depletion near impurities.

Findings

Spectral function analysis reveals the polaron-molecule transition in 3D.

Medium atom spectral functions can indicate polaron crossover.

Depletion of Bose-Einstein condensate near impurities observed.

Abstract

The notion of a polaron, originally introduced in the context of electrons in ionic lattices, helps us to understand how a quantum impurity behaves when being immersed in and interacting with a many-body background. We discuss the impact of the impurities on the medium particles by considering feedback effects from polarons that can be realized in ultracold quantum gas experiments. In particular, we exemplify the modifications of the medium in the presence of either Fermi or Bose polarons. Regarding Fermi polarons we present a corresponding many-body diagrammatic approach operating at finite temperatures and discuss how mediated two- and three-body interactions are implemented within this framework. Utilizing this approach, we analyze the behavior of the spectral function of Fermi polarons at finite temperature by varying impurity-medium interactions as well as spatial dimensions from three to one. Interestingly, we reveal that the spectral function of the medium atoms could be a useful quantity for analyzing the transition/crossover from attractive polarons to molecules in three-dimensions. As for the Bose polaron, we showcase the depletion of the background Bose-Einstein condensate in the vicinity of the impurity atom. Such spatial modulations would be important for future investigations regarding the quantification of interpolaron correlations in Bose polaron problems.