# Quantum Thermal Machine as a Thermometer

## TL;DR

This paper introduces a quantum thermal machine-based thermometer capable of precise low-temperature measurements down to 15 mK, leveraging quantum Fisher information for near-optimal performance in complex systems.

## Contribution

It proposes a novel thermometry method using quantum thermal machines that works without detailed knowledge of coupling constants and is implementable with circuit QED technology.

## Key findings

- Achieves thermometry down to ~15 mK with realistic parameters.
- Operates effectively without precise thermalization between components.
- Close to the theoretical limit set by quantum Fisher information.

## Abstract

We propose the use of a quantum thermal machine for low-temperature thermometry. A hot thermal reservoir coupled to the machine allows for simultaneously cooling the sample while determining its temperature without knowing the model-dependent coupling constants. In its most simple form, the proposed scheme works for all thermal machines which perform at Otto efficiency and can reach Carnot efficiency. We consider a circuit QED implementation which allows for precise thermometry down to $\sim$15 mK with realistic parameters. Based on the quantum Fisher information, this is close to the optimal achievable performance. This implementation demonstrates that our proposal is particularly promising in systems where thermalization between different components of an experimental setup cannot be guaranteed.