Quantum heat engines and information

TL;DR

This paper analyzes quantum heat engines using bipartite quantum systems, expressing work in terms of temperature and quantum information, revealing how entanglement influences work extraction and highlighting quantum nonlocality effects.

Contribution

It derives an explicit formula for work in bipartite quantum engines, linking quantum entanglement with the ability to extract work locally or globally.

Findings

Positive net work depends on quantum state properties.

A critical entanglement threshold exists for local work extraction.

Quantum nonlocality manifests in work extraction limitations.

Abstract

Recently, Zhang {\em et al.} [PRA, {\bf 75}, 062102 (2007)] extended Kieu's interesting work on the quantum Otto engine [PRL, {\bf 93}, 140403 (2004)] by considering as working substance a bipartite quantum system $AB$ composed of subsystems $A$ and $B$. In this paper, we express the net work done $W_{AB}$ by such an engine explicitly in terms of the macroscopic bath temperatures and information theoretic quantities associated with the microscopic quantum states of the working substance. This allows us to gain insights into the dependence of positive $W_{AB}$ on the quantum properties of the states. We illustrate with a two-qubit XY chain as the working substance. Inspired by the expression, we propose a plausible formula for the work derivable from the subsystems. We show that there is a critical entanglement beyond which it is impossible to draw positive work locally from the individual subsystems while $W_{AB}$ is positive. This could be another interesting manifestation of quantum nonlocality.