Thermodynamic universality of quantum Carnot engines

TL;DR

This paper demonstrates that quantum features like coherence and entanglement do not violate the Carnot efficiency limit, but require redefining heat to include their thermodynamic costs, supported by numerical examples in optomechanics.

Contribution

It shows that quantum effects do not surpass classical thermodynamic limits when properly accounting for their thermodynamic costs.

Findings

Quantum coherence and entanglement do not increase efficiency beyond Carnot limit.

Redefinition of heat is necessary to include costs of maintaining quantum features.

Numerical illustration using optomechanical systems supports the theoretical results.

Abstract

The Carnot statement of the second law of thermodynamics poses an upper limit on the efficiency of all heat engines. Recently, it has been studied whether generic quantum features such as coherence and quantum entanglement could allow for quantum devices with efficiencies larger than the Carnot efficiency. The present study shows that this is not permitted by the laws of thermodynamics. In particular, we will show that rather the definition of heat has to be modified to account for the thermodynamic cost for maintaining coherence and entanglement. Our theoretical findings are numerically illustrated for an experimentally relevant example from optomechanics.