Researchers show that adding a degenerate optical parametric amplifier (DOPA) to a simple quantum–battery setup can increase the stored energy and the average charging power. The study models a charger and a battery as two coupled harmonic oscillators. The charger is driven both by a ordinary coherent drive and by the DOPA, while the two modes share one or two common reservoirs that mediate dissipation.

In the model, the DOPA is a nonlinear optical device that generates pairs of down-converted photons. In plain terms, it provides parametric amplification and can create squeezed states, which alter the flow of energy into the charger. The charger and battery are also coupled coherently, and each mode loses energy to the environment at its own rate. By treating the reservoirs and eliminating their fast dynamics, the authors obtain an effective dissipative coupling between charger and battery.

The dissipative coupling produced by the shared reservoirs can be nonreciprocal. That means energy flows preferentially from the charger to the battery and backflow is suppressed. The DOPA adds another control knob: its nonlinear gain and the phase of the pump field change how much energy is injected and how the charging proceeds. The authors report that, in the stable below-threshold operating regime of the DOPA (where the amplifier boosts signals but does not self-oscillate), both the battery energy and the average charging power can be enhanced.

These improvements persist whether the two modes share a single common reservoir or two distinct common reservoirs. The paper derives steady-state expressions and shows that further gains come from tuning the asymmetry of the dissipative couplings — in other words, from optimizing how strongly each mode couples to the reservoirs. The analysis is done within an open-system framework and uses adiabatic elimination of the reservoirs to obtain the effective directional interaction.