# Strong coupling Bose polarons in a two-dimensional gas

## TL;DR

This paper investigates Bose polarons in a two-dimensional gas using quantum Monte Carlo methods, revealing the existence of two quasiparticle branches and how strong interactions influence their properties and stability.

## Contribution

It provides the first detailed quantum Monte Carlo analysis of 2D Bose polarons, characterizing their binding energy, effective mass, and quasiparticle residue across interaction regimes.

## Key findings

- Existence of lower and upper quasiparticle branches.
- Strong interactions lead to vanishing quasiparticle residue.
- Deep bound states involve many particles from the bath.

## Abstract

We study the properties of Bose polarons in two dimensions using quantum Monte Carlo techniques. Results for the binding energy, the effective mass, and the quasiparticle residue are reported for a typical strength of interactions in the gas and for a wide range of impurity-gas coupling strengths. A lower and an upper branch of the quasiparticle exist. The lower branch corresponds to an attractive polaron and spans from the regime of weak coupling where the impurity acts as a small density perturbation of the surrounding medium to deep bound states which involve many particles from the bath and extend as far as the healing length. The upper branch corresponds to an excited state where due to repulsion a low-density bubble forms around the impurity but might be unstable against decay into many-body bound states. Interaction effects strongly affect the quasiparticle properties of the polaron. In particular, in the strongly correlated regime, the impurity features a vanishing quasiparticle residue, signaling the transition from an almost free quasiparticle to a bound state involving many atoms from the bath.