Extracting work from correlated many-body quantum systems

TL;DR

This paper investigates how correlations in many-body quantum systems can enhance work extraction, showing that classical correlations alone can enable near-complete work extraction in large systems without quantum entanglement.

Contribution

It introduces a measure of correlations in translationally invariant systems using Matrix Product Operators and demonstrates that classical correlations can significantly increase extractable work.

Findings

Complete work extraction is possible at small correlation strengths in large systems.

Quantum entanglement is not necessary for enhanced work extraction.

A rigorous formulation of the typicality argument for maximum work extraction is provided.

Abstract

The presence of correlations in the input state of a non-interacting many-body quantum system can lead to an increase in the amount of work we can extract from it under global unitary processes (ergotropy). The present work explore such effect on translationally invariant systems relaying on the Matrix Product Operator formalism to define a measure of how much they are correlated. We observe that in the thermodynamic limit of large number of sites, complete work extraction can be attained for relatively small correlation strength (a reduction of a 2 factor in dB unit). Most importantly such an effect appears not to be associated with the presence of quantum correlations (e.g. entanglement) in the input state (classical correlation sources), and to be attainable by only using incoherent ergotropy. As a byproduct of our analysis we also present a rigorous formulation of the heuristic typicality argument first formulated in [Alicki and Fannes, 2013], which gives the maximum work extractable for a set of many identical quantum systems in the asymptotic limit.