Description of quantum coherence in thermodynamic processes requires constraints beyond free energy

TLDR

Recent studies have developed fundamental limitations on nanoscale thermodynamics, expressed as a set of independent free‑energy relations. Here we show that free‑energy relations cannot properly describe quantum coherence in thermodynamic processes. By casting time‑asymmetry as a quantifiable, fundamental resource of a quantum state, we derive an additional, independent set of thermodynamic constraints that naturally extend the existing ones. These asymmetry relations show that the traditional Szilard engine argument does not extend to quantum coherences, that only relational coherences in multipartite systems can contribute to thermodynamic work, that coherence transformations are always irreversible, and that the results reveal structural parallels between thermodynamics and entanglement theory.

Abstract

Recent studies have developed fundamental limitations on nanoscale thermodynamics, in terms of a set of independent free energy relations. Here we show that free energy relations cannot properly describe quantum coherence in thermodynamic processes. By casting time-asymmetry as a quantifiable, fundamental resource of a quantum state we arrive at an additional, independent set of thermodynamic constraints that naturally extend the existing ones. These asymmetry relations reveal that the traditional Szilard engine argument does not extend automatically to quantum coherences, but instead only relational coherences in a multipartite scenario can contribute to thermodynamic work. We find that coherence transformations are always irreversible. Our results also reveal additional structural parallels between thermodynamics and the theory of entanglement.