Negative contributions to entropy production induced by quantum coherences

TL;DR

This paper reveals that quantum coherences in degenerate systems can induce negative entropy production contributions, significantly impacting thermodynamics and heat flow, with implications for quantum thermal machines.

Contribution

It uncovers new negative quantum contributions to entropy production in degenerate quantum systems and explores their thermodynamic consequences.

Findings

Negative quantum contributions to entropy production can occur in degenerate systems.

Horizontal coherences can reverse population convergence to thermal equilibrium.

A complementarity relation links coherences and population dynamics.

Abstract

The entropy production in dissipative processes is the essence of the arrow of time and the second law of thermodynamics. For dissipation of quantum systems, it was recently shown that the entropy production contains indeed two contributions: a classical one and a quantum one. Here we show that for degenerate (or near-degenerate) quantum systems there are additional quantum contributions which, remarkably, can become negative. Furthermore, such negative contributions are related to significant changes in the ongoing thermodynamics. This includes phenomena such as generation of coherences between degenerate energy levels (called horizontal coherences), alteration of energy exchanges and, last but not least, reversal of the natural convergence of the populations toward the thermal equilibrium state. Going further, we establish a complementarity relation between horizontal coherences and population convergence, particularly enlightening for understanding heat flow reversals. Conservation laws of the different types of coherences are derived. Some consequences for thermal machines and resource theory of coherence are suggested.