# Spectral signatures of non-thermal baths in quantum thermalization

## TL;DR

This paper investigates how heat-exchange coherences in non-thermal baths influence the spectral response of quantum probes, proposing experimental methods to assess apparent temperature and thermalization time, with applications in quantum simulation.

## Contribution

It introduces the concept of heat-exchange coherences affecting spectral signatures and demonstrates their use in measuring bath properties and simulating quantum phenomena.

## Key findings

- Heat-exchange coherences modify the spectral response of quantum probes.
- Power spectrum analysis can assess the apparent temperature of non-thermal baths.
- Repeated interactions enable quantum simulation of resonance fluorescence.

## Abstract

We show that certain coherences, termed as heat-exchange coherences, which contribute to the thermalization process of a quantum probe in a repeated interactions scheme, can modify the spectral response of the probe system. We suggest to use the power spectrum as a way to experimentally assess the apparent temperature of non-thermal atomic clusters carrying such coherences and also prove that it is useful to measure the corresponding thermalization time of the probe, assuming some information is provided on the nature of the bath. We explore this idea in two examples in which the probe is assumed to be a single-qubit and a single-cavity field mode. Moreover, for the single-qubit case, we show how it is possible to perform a quantum simulation of resonance fluorescence using such repeated interactions scheme with clusters carrying different class of coherences.