# Creation of Rydberg Polarons in a Bose Gas

## TL;DR

This paper reports the spectroscopic observation of Rydberg polarons in a Bose gas, revealing universal spectral behavior and resolving polyatomic Rydberg molecules, advancing understanding of impurity-boson interactions.

## Contribution

It introduces the creation and spectroscopic analysis of Rydberg polarons in a Bose-Einstein condensate, with a theoretical framework that accurately describes observed spectral features and excited molecular states.

## Key findings

- Observation of Rydberg polarons in Sr Bose gas.
- Universal spectral lineshape due to absence of p-wave resonance.
- Experimental resolution and theoretical reproduction of polyatomic Rydberg molecules.

## Abstract

We report spectroscopic observation of Rydberg polarons in an atomic Bose gas. Polarons are created by excitation of Rydberg atoms as impurities in a strontium Bose-Einstein condensate. They are distinguished from previously studied polarons by macroscopic occupation of bound molecular states that arise from scattering of the weakly bound Rydberg electron from ground-state atoms. The absence of a $p$-wave resonance in the low-energy electron-atom scattering in Sr introduces a universal behavior in the Rydberg spectral lineshape and in scaling of the spectral width (narrowing) with the Rydberg principal quantum number, $n$. Spectral features are described with a functional determinant approach (FDA) that solves an extended Fr\"{o}hlich Hamiltonian for a mobile impurity in a Bose gas. Excited states of polyatomic Rydberg molecules (trimers, tetrameters, and pentamers) are experimentally resolved and accurately reproduced with FDA.