Extracting work from correlated many-body quantum systems

The presence of correlations in the input state of a noninteracting 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 explores such effect on translationally invariant systems relying 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 units). Most importantly, such an effect appears to not be associated with the presence of quantum correlations (e.g., entanglement) in the input state (classical correlation suffices), 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 by Alicki and Fannes [R. Alicki and M. Fannes, Phys. Rev. E 87, 042123 (2013)10.1103/PhysRevE.87.042123], which gives the maximum work that is extractable for a set of many identical quantum systems in the asymptotic limit.