Performance enhancement of a quantum battery via frequency detuning

We study a charger-battery system consisting of two qubits coupled to a common structured reservoir, aimed at revealing how their frequency detunings from the main reservoir frequency and their coupling strengths to the reservoir affect the performance of the quantum battery (QB). It is found that an equal coupling of the qubits to the reservoir is beneficial for enhancing the charging performance. When the frequency detunings are not very large, we have the optimal extractable work and charging efficiency if the detuning of the QB is smaller than that of the charger. But when they are large, the equal detunings yield the optimal extractable work and charging efficiency, and the QB is efficiently charged independently of the system-reservoir coupling strength. Moreover, the increased charging time due to enlarged detunings can be efficiently offset by increasing the system-reservoir coupling strength.