Experimental demonstration of quantum effects in the operation of microscopic heat engines

TL;DR

This paper experimentally demonstrates quantum thermodynamic signatures, such as power boost from coherence and equivalence of heat engine types, using nitrogen-vacancy centers in diamond, marking the first observation of such quantum effects.

Contribution

It provides the first experimental evidence of quantum thermodynamic signatures in microscopic heat engines using NV centers.

Findings

Demonstrated coherence-induced power boost in quantum heat engines

Observed thermodynamic equivalence of different quantum heat engine types

First experimental observation of quantum thermodynamic signatures

Abstract

The heat engine, a machine that extracts useful work from thermal sources, is one of the basic theoretical constructs and fundamental applications of classical thermodynamics. The classical description of a heat engine does not include coherence in its microscopic degrees of freedom. By contrast, a quantum heat engine might possess coherence between its internal states. Although the Carnot efficiency cannot be surpassed, and coherence can be performance degrading in certain conditions, it was recently predicted that even when using only thermal resources, internal coherence can enable a quantum heat engine to produce more power than any classical heat engine using the same resources. Such a power boost therefore constitutes a quantum thermodynamic signature. It has also been shown that the presence of coherence results in the thermodynamic equivalence of different quantum heat engine types, an effect with no classical counterpart. Microscopic heat machines have been recently implemented with trapped ions, and proposals for heat machines using superconducting circuits and optomechanics have been made. When operated with standard thermal baths, however, the machines implemented so far have not demonstrated any inherently quantum feature in their thermodynamic quantities. Here we implement two types of quantum heat engines by use of an ensemble of nitrogen-vacancy centres in diamond, and experimentally demonstrate both the coherence power boost and the equivalence of different heat-engine types. This constitutes the first observation of quantum thermodynamic signatures in heat machines.