Dissipative Charging of a Quantum Battery

We show that a cyclic unitary process can extract work from the thermodynamic equilibrium state of an engineered quantum dissipative process. Systems in the equilibrium states of these processes serve as batteries, storing energy. The dissipative process that brings the battery to the active equilibrium state is driven by an agent that couples the battery to thermal systems. The second law of thermodynamics imposes a work cost for the process; however, no work is needed to keep the battery in that charged state. We consider simple examples of these batteries and discuss situations in which the charged state has full population inversion, in which case the extractable work is maximal, and circumstances in which the efficiency of the process is maximal.

Figure 1

Population inversion in the equilibration process for the single-qubit battery. (Upper) Populations of the ground ($p_g$) and excited ($p_e$) states for each iteration step $n$. (Lower) Work ($W_n$), heat flow ($Q_n$), and entropy production (${\mathrm{\Sigma }}_n$) for each step $n$. The initial state of the battery is a thermal state, that is, an identical state to that of the auxiliary baths. We consider for these plots $\tau =0.1$, $a=\sqrt{10}$, $h=1.5$, and $\beta =1$. The continuous lines are a guide for the eyes.