Maximal work extraction from quantum systems

TL;DR

This paper derives the maximum work extractable from quantum systems, called ergotropy, showing its dependence on the system's state and highlighting scenarios where quantum properties alter thermodynamic expectations.

Contribution

The paper introduces the concept of ergotropy, providing a quantum mechanical bound on work extraction and relating it to majorization and correlations.

Findings

Ergotropy is expressed in terms of the density matrix and Hamiltonian.

More major states can yield more work.

Quantum correlations can increase or decrease ergotropy.

Abstract

Thermodynamics teaches that if a system initially off-equilibrium is coupled to work sources, the maximum work that it may yield is governed by its energy and entropy. For finite systems this bound is usually not reachable. The maximum extractable work compatible with quantum mechanics (``ergotropy'') is derived and expressed in terms of the density matrix and the Hamiltonian. It is related to the property of majorization: more major states can provide more work. Scenarios of work extraction that contrast the thermodynamic intuition are discussed, e.g. a state with larger entropy than another may produce more work, while correlations may increase or reduce the ergotropy.