Quantum batteries at the verge of a phase transition

Abstract Starting from the observation that reduced state of a system strongly coupled to bath is, in general, an athermal state, we introduce and study cyclic battery–charger quantum device is thermal equilibrium, or ground during charge storing stage. The cycle has four stages: equilibrium storage stage interrupted by disconnecting battery charger, then work extracted battery, reconnected with charger; finally, brought back equilibrium. At no point are correlations artificially erased. We case where charger together comprise spin-1/2 Ising chain, show main characteristics—the energy thermodynamic efficiency—can be enhanced operating close phase transition point. When just single spin, find output efficiency scaling behavior at criticality derive corresponding critical exponents. Due always present between operations equivalent perspective can entail different energetic costs for switching coupling. This happens only when coupling term does not commute battery’s bare Hamiltonian, use this purely leverage further optimize performance device.