Scaling law for optimal excitation storage and superradiant release in waveguide QED systems

Efficiently storing and retrieving quantum information is a fundamental challenge in quantum technologies, including quantum batteries and networks. This paper investigates a waveguide QED platform consisting of two spatially separated ensembles of two-level emitters coupled to a semi-infinite waveguide. The first ensemble is coherently driven and acts as a reservoir, while the second ensemble is positioned at a dissipative node, rendering it subradiant and capable of storing excitations. The authors analyze the system's dynamics using a Markovian master equation, focusing on how collective light-matter interactions—specifically the interplay between coherent driving, dissipation, and inter-ensemble coupling—can be harnessed to optimize excitation transfer.

A central challenge in many-body quantum systems is that complex inter-ensemble correlations often invalidate simple mean-field models. However, the authors discover that when the driven ensemble is much larger than the storage ensemble (N1 >> N2), the system enters a nearly correlation-free regime. In this limit, the driven ensemble behaves effectively as a classical excitation source. By analyzing the connected inter-ensemble correlator, the researchers derive a scaling law showing that the optimal driving strength required for maximal excitation transfer scales linearly with the number of emitters in the driven ensemble (N1). This allows for near-complete population inversion in the storage ensemble, providing a robust mechanism for quantum energy storage.

The study demonstrates that coherent and dissipative collective interactions can be jointly managed to create programmable nonequilibrium dynamics. By tuning the driving strength according to the identified scaling law, the system can effectively suppress the buildup of detrimental quantum correlations during the early stages of transfer. The authors further propose a three-stage protocol—storage, protection via detuning, and on-demand release—that leverages the superradiant decay channel of the driven ensemble to enhance photon emission. These findings offer a clear, scalable strategy for designing high-efficiency quantum memories and energy-storage devices in waveguide-based architectures.