Bose polarons in the strongly interacting regime

TL;DR

This study investigates Bose polarons formed by impurity atoms in a Bose-Einstein condensate, revealing their properties in the strongly interacting regime using RF spectroscopy and Feshbach resonance.

Contribution

It provides the first detailed characterization of Bose polarons in the strongly interacting regime, including energy, spectral width, and lifetime measurements.

Findings

Polaron width remains narrow in the attractive branch despite diverging scattering length

Energy and lifetime of polarons are measured across interaction regimes

Spectral properties differ between attractive and repulsive branches

Abstract

When an impurity is immersed in a Bose-Einstein condensate, impurity-boson interactions are expected to dress the impurity into a quasiparticle, the Bose polaron. We superimpose an ultracold atomic gas of $^{87}$Rb with a much lower density gas of fermionic $^{40}$K impurities. Through the use of a Feshbach resonance and RF spectroscopy, we characterize the energy, spectral width and lifetime of the resultant polaron on both the attractive and the repulsive branches in the strongly interacting regime. The width of the polaron in the attractive branch is narrow compared to its binding energy, even as the two-body scattering length formally diverges.