Quantum coherence and entanglement in wireless quantum batteries

Research Question and Approach

This paper investigates the charging dynamics and thermodynamic performance of a wireless quantum battery (QB) system. Unlike traditional architectures that require physical wires or close proximity, this model uses a common structured bosonic environment—such as an optical cavity—to mediate energy transfer between a quantum charger and a quantum battery. The authors employ a unified resource-theoretic analysis to examine how non-Markovian memory effects and coupling symmetry (the relative strength of interaction between each qubit and the environment) regulate energy storage and the evolution of quantum resources like coherence and entanglement.

Charging Dynamics and Resource Evolution

The study identifies two distinct regimes of operation. In the Markovian weak-coupling regime, the system experiences monotonic decay of first-order coherence. However, the authors demonstrate a compensatory mechanism where the reconstruction of l1-norm coherence sustains energy transport. In contrast, the non-Markovian strong-coupling regime utilizes environmental backflow to create a cooperative resonance. In this state, entanglement and stored energy oscillate in perfect synchronization, preventing the energy saturation typically seen in memoryless systems.

The Role of Coupling Symmetry

Coupling symmetry is identified as a critical control parameter for system performance. Asymmetric coupling, specifically configured to favor the battery, is shown to optimize energy gain in memoryless environments. Conversely, symmetric coupling under strong interactions unlocks a dark-state protection mechanism. This effectively traps energy within a decoherence-free subspace, significantly mitigating the self-discharging issues that plague open quantum systems.

Thermodynamic Implications

Through a thermodynamic analysis using ergotropy, the authors clarify the functional roles of different coherence measures. They establish that first-order coherence acts as the activation threshold for incoherent work, while l1-norm coherence serves as the essential fuel for coherent work extraction. These findings provide a theoretical framework for engineering environment-assisted quantum energy storage devices that are more robust against environmental noise.