Frictional work and entropy production in integrable and non-integrable spin chains
The maximum work extractable from a quantum system is achieved when the system is driven adiabatically. Frictional work $\langle W\rangle_\mathrm{fric}$ then quantifies the difference in work output between adiabatic and non-adiabatic driving. Here we show that frictional work in a non-integrable spin chain is well-characterized by the diagonal entropy production $ΔS_\mathrm{d}$ associated with the build up of quantum coherence. We show that, over a broad range of parameters, $\langle W\rangle_\mathrm{fric}\approx T_τΔS_\mathrm{d}$, with $T_τ$ the effective temperature of the final time-evolved state. The relationship breaks down for fast protocols at low temperatures, in which case frictional work is instead well-described by the quantum relative entropy between the time-evolved state and a Gibbs-state approximation of the adiabatic state. We compare our results to those obtained from an integrable spin chain, in which case the system is no longer described by a single temperature. In this case, the frictional work is described by a sum of terms for each independent subspace of the spin chain, which are at different effective temperatures. Finally, we show how integrability breaking can enhance work extraction in the adiabatic limit, but degrade work extraction in sufficiently non-adiabatic regimes.