Phase-Locked Quantum Battery Charging via Dissipative Mode Selection

We investigate how dynamical instability and reservoir engineering can be harnessed to enhance the quality of quantum-battery charging in a bosonic two-mode system. We show that reservoir-engineered dissipative coupling selectively amplifies a single unstable quasi-dark mode, enabling phase-locked exponential charging at a reduced gain threshold, whereas coherent coupling can amplify two frequency-split unstable modes, resulting in persistent beating. This dissipative mode selection yields a near-unit ergotropy fraction and a substantially higher work-like signal-to-noise ratio (SNR), defined as ergotropy divided by the standard deviation of battery energy. Although optimizing the driving frequency enables coherent coupling to achieve faster charging and higher ergotropy power, dissipative coupling retains its advantage in the work-like SNR. An exact finite-time source-noise relation reveals that this advantage arises from a more constructive accumulation of coherent driving relative to incoherent fluctuations. Our results establish dissipative mode selection as a promising route to high-quality quantum-battery charging.