Heidelberg 2015 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 50: Quantum Information: Concepts and Methods VII

Q 50.1: Talk

Thursday, March 26, 2015, 11:00–11:15, K/HS1

Weak thermal contact is not universal for work extraction — •Henrik Wilming, Rodrigo Gallego, and Jens Eisert — Dahlem Center for Complex Quantum Systems, Freie Universität Berlin, 14195 Berlin, Germany

The free energy difference to the equilibrium state limits the amount of work that can be extracted on average from a system out of thermal equilibrium. This bound can be saturated by protocols putting the system and a bath into weak thermal contact (WTC), i.e., bringing the system into a Gibbs state at the bath's temperature. Surprisingly, the same bound holds true when the contact to the heat bath is modelled by more general proccesses, which have the only restriction that when the system already is in equilibrium, it cannot be brought out of it. In that sense, WTC is universal for work extraction.

In this work, we introduce the study of work-extraction protocols under restrictions encountered in realistic devices at the nano-scale. We consider limitations on the maximum energies in the system and on the local structure of many-body Hamiltonians. Remarkably, we find that WTC then loses its universality: There is a gap between the work the can be extracted with WTC and with more general oper- ations. Our work highlights the relevance of operational frameworks such as those of thermal operations and Gibbs preserving maps, as they can improve the performance of thermal machines, and provides a unifying framework of incorporating natural restrictions in quantum thermodynamics.