# Steering heat engines: a truly quantum Maxwell demon

## TL;DR

This paper proposes a method to verify the quantum nature of thermal machines by using a steering inequality, demonstrating that quantum correlations enable work extraction beyond classical limits.

## Contribution

It introduces a steering inequality as a criterion to distinguish truly quantum thermal machines from classical ones, linking quantum correlations to work extraction.

## Key findings

- Quantum Szilard engine can violate the steering inequality
- Classical engines always admit an objective local description
- Quantum correlations enable surpassing classical work bounds

## Abstract

We address the question of verifying the quantumness of thermal machines. A Szil\'ard engine is truly quantum if its work output cannot be described by a local hidden state (LHS) model, i. e. an objective local statistical ensemble. Quantumness in this scenario is revealed by a steering-type inequality which bounds the classically extractable work. A quantum Maxwell demon can violate that inequality by exploiting quantum correlations between the work medium and the thermal environment. While for a classical Szil\'ard engine an objective description of the medium always exists, any such description can be ruled out by a steering task in a truly quantum case.