# Bose polarons near quantum criticality

## TL;DR

This study investigates Bose polarons near quantum criticality by immersing impurities in a Bose-Einstein condensate and using spectroscopy to observe their quasiparticle behavior and breakdown near the critical temperature.

## Contribution

It demonstrates the formation and decay of Bose polarons near quantum criticality, revealing linear temperature dependence of their spectral width at the Planckian scale.

## Key findings

- Well-defined quasiparticles form far below the critical temperature.
- Spectral width increases linearly with temperature at the Planckian scale.
- Quasiparticle picture breaks down near the critical temperature.

## Abstract

The emergence of quasiparticles in strongly interacting matter represents one of the cornerstones of modern physics. However, when different phases of matter compete near a quantum critical point, the very existence of quasiparticles comes under question. Here we create Bose polarons near quantum criticality by immersing atomic impurities in a Bose-Einstein condensate (BEC) with near-resonant interactions. Using locally-resolved radiofrequency spectroscopy, we probe the energy, spectral width, and short-range correlations of the impurities as a function of temperature. Far below the superfluid critical temperature, the impurities form well-defined quasiparticles. However, their inverse lifetime, given by their spectral width, is observed to increase linearly with temperature at the Planckian scale $\frac{k_B T}{\hbar}$, a hallmark of quantum critical behavior. Close to the BEC critical temperature, the spectral width exceeds the binding energy of the impurities, signaling a breakdown of the quasiparticle picture.