Driven-dissipative quantum battery with nonequilibrium reservoirs

We investigate a quantum battery system under both external driving and dissipation. The system consists of a coupled two-level charger and battery immersed in nonequilibrium fermionic reservoirs. By considering the changes in the energy spectrum induced by external driving and charger-battery coupling in a non-perturbative manner, we go beyond the secular approximation to derive the Redfield master equation. In the nonequilibrium scenario, both charging efficiency and power of the quantum battery can be optimized through a compensation mechanism. When the charger and battery are off-resonance, a significant chemical potential difference between the reservoirs, which characterizes the degree of nonequilibrium, plays a crucial role. Specifically, the charger's frequency should be higher (lower) than that of the battery when the average chemical potential is negative (positive) to achieve enhanced charging efficiency and power under strong nonequilibrium conditions. Remarkably, the efficiency in the nonequilibrium case can surpass that in the equilibrium setup. Moreover, we find no positive correlation between entanglement and efficiency, challenging the prevailing assumption that entanglement necessarily enhances the performance of quantum devices. Our results provide insights into the design and optimization of quantum batteries in nonequilibrium open systems.