Noise is not always detrimental: quantum battery capacity enhanced by the Unruh effect in noninertial frames

Quantum battery capacity, as a measure of the energetic range available to a quantum system, can exhibit nontrivial behavior in noninertial frames and noisy environments. This study focuses on a bipartite mixed state and explores how the Unruh effect and local environmental noise modify quantum battery capacity. Within the approximation that retains a single field mode for Dirac fields and for a two-qubit Ising battery model, we find that the Unruh channel can enhance the capacity of the state accessible to accelerated observers. When local phase-flip, bit-flip, and depolarizing channels are additionally applied, the capacity is generally suppressed, with details that depend on the noise model. Bit-flip noise modifies the population structure more directly than phase-flip noise and can qualitatively change the dependence of capacity on acceleration. Under complete depolarization, the capacity vanishes. These results concern the transformation of the battery state caused by acceleration and noise; they do not describe a charging or discharging protocol that evolves in time. Our findings provide a perspective specific to the present model on quantum battery capacity in noninertial and noisy settings.