Correlated quantum machines beyond the standard second law

Abstract: The laws of thermodynamics strongly restrict the performance of thermal machines. Standard thermodynamics, initially developed for uncorrelated macroscopic systems, does not hold for microscopic systems correlated with their environments. We here derive exact generalized laws of quantum thermodynamics for arbitrary, time-periodic, open systems that account for all possible correlations between all involved parties. We demonstrate the existence of two basic modes of engine operation: the usual thermal case, where heat is converted into work, and a novel athermal regime, where work is extracted from entropic resources, such as system-bath correlations. In the latter regime, the efficiency of a quantum engine is not bounded by the usual Carnot formula. Our results provide a unified formalism to determine the efficiency of correlated microscopic thermal devices.