Competing few-body correlations in ultracold Fermi polarons

TL;DR

This paper reviews recent advances in understanding how competing few-body correlations influence the properties of ultracold Fermi polarons, highlighting transitions and exotic phases in mass-balanced and imbalanced systems.

Contribution

It introduces a unified variational framework to analyze competing few-body correlations in Fermi polarons, encompassing both equal and unequal mass cases.

Findings

Polaron-molecule transition driven by two-body correlations.

Finite momentum and degeneracy of molecule states.

Smooth crossover from polaron to dressed clusters in mass-imbalanced systems.

Abstract

Polaron, a typical quasi-particle that describes a single impurity dressed with surrounding environment, serves as an ideal platform for bridging few- and many-body physics. In particular, different few-body correlations can compete with each other and lead to many intriguing phenomena. In this work, we review the recent progresses made in understanding few-body correlation effects in attractive Fermi polarons of ultracold gases. By adopting a unified variational ansatz that incorporates different few-body correlations in a single framework, we will discuss their competing effects in Fermi polarons when the impurity and majority fermions have the same or different masses. For the equal-mass case, we review the nature of polaron-molecule transition that is driven by two-body correlations, and especially highlight the finite momentum character and huge degeneracy of molecule states. For the mass-imbalanced case, we focus on the smooth crossover between polaron and various dressed clusters that originate from high-order correlations. These competing few-body correlations reviewed in Fermi polarons suggest a variety of exotic new phases in the corresponding many-body system of Fermi-Fermi mixtures.