Francesco Pellegrino - Università di Catania

Circuit Quantum Electrodynamics and Quantum Energy Storage in Two-Dimensional Josephson Junctions

Hybrid superconductor–semiconductor platforms based on two-dimensional materials provide a promising route toward scalable and tunable quantum devices. In this work, we investigate the interaction between a short ballistic planar Josephson junction and a quantum LC resonator, focusing on graphene-based systems as a representative example. 

Within a mean-field description, we analyze the coupled light–matter system as a function of the interaction strength, carrier density, and temperature. We show that the inductive coupling between the resonator and the Josephson current strongly modifies the current–phase relation and can induce signatures of spontaneous time-reversal symmetry breaking. In addition, we determine the low-energy spectrum of hybridized collective excitations arising from the interplay between Andreev bound states and cavity photons.

We further explore the same architecture in the context of quantum energy storage. The Andreev bound states naturally behave as a collection of non-degenerate two-level systems coupled to the resonator field, leading to a Dicke-like quantum battery implementation. In this regime, the system supports both single-photon and two-photon resonant processes. Moreover, the inductive coupling generates unconventional longitudinal interaction terms absent in the standard Dicke model. These additional contributions can significantly enhance the stored energy within suitable parameter regimes.

Our results demonstrate that two-dimensional material-based Josephson junctions constitute a versatile platform for cavity quantum electrodynamics and quantum energy-storage applications, combining gate tunability, strong light–matter coupling, and engineered superconducting quantum states.