Graphene Josephson Junctions Point Toward a More Solid-State Quantum Battery

A new preprint gives the quantum-battery field something it badly needs: a bridge between elegant collective-charging theory and a device geometry that condensed-matter labs already know how to build. In Quantum Batteries in two-dimensional material-based Josephson Junctions, V. Varrica, G. Gemme, F. M. D. Pellegrino, E. Paladino, M. Sassetti, and D. Ferraro propose a battery made from a two-dimensional-material Josephson junction, using graphene as the representative platform, inductively coupled to a superconducting resonator.

The paper, submitted to arXiv on May 21, 2026 as arXiv:2605.22582, is theoretical. It is not a claim that graphene chips are about to replace lithium-ion packs. Its importance is more specific and, for quantum-energy research, more interesting: it shows how a familiar solid-state object can naturally supply many microscopic two-level systems, tune their energy splittings with superconducting phase, and charge them through cavity photons in ways that resemble Dicke quantum batteries.

The key move is to treat Andreev bound states inside a short graphene Josephson junction as the battery cells, while a microwave resonator acts as the charger.

That architecture puts quantum batteries closer to the toolbox of circuit quantum electrodynamics, or cQED, where superconducting resonators, Josephson weak links, microwave spectroscopy, and phase-biased devices are already standard experimental languages.

Why quantum batteries are looking for better hardware

A quantum battery is not a better AA cell. It is a small quantum system that can store usable energy in its excited states and release that energy to another quantum device. The motivation is most compelling at the nanoscale: quantum sensors, superconducting circuits, and future quantum processors may need energy delivery that is fast, coherent, and integrated directly into the device layer.

The field began with simple models of many two-level systems, including the influential work of Robert Alicki and Mark Fannes on entanglement-enhanced extractable work. Since then, theorists have explored spin chains, harmonic oscillators, superconducting circuits, collisional models, and cavity-based schemes. A 2024 Reviews of Modern Physics colloquium by Campaioli, Gherardini, Quach, Polini, and Andolina summarizes the broad landscape, while experiments such as Quach and colleagues’ 2022 Science Advances demonstration of superabsorption in an organic microcavity showed that collective optical effects can be measured in battery-like settings.

One reason the Dicke model keeps returning in this literature is that it offers a clean story: many matter-like two-level systems couple to a shared radiation mode. If that collective coupling is engineered well, the charging power can scale more favorably than charging each unit independently. Ferraro, Campisi, Andolina, Pellegrini, and Polini’s 2018 Physical Review Letters paper on high-power collective charging helped make this cavity-battery picture a standard reference point.

The hard part is turning the model into a controllable solid-state object. Molecules in a cavity, artificial atoms, and spin systems each have strengths. The 2026 Josephson-junction proposal asks whether the “battery cells” could instead be Andreev bound states in a planar superconducting weak link.

The device: a graphene weak link in a superconducting ring

The proposed system is a superconducting ring interrupted by a short superconductor–semiconductor Josephson junction. The authors focus on graphene, a two-dimensional material with a high Fermi velocity and gate-tunable carrier density, although they emphasize that the formalism applies more broadly to planar junctions. The ring is inductively coupled to a superconducting LC resonator. In the energy-language of the paper, the junction is the quantum battery and the resonator is the charger.

The microscopic battery cells are Andreev bound states. These are subgap electronic states localized in the normal region of a Josephson junction. They arise because an electron entering a superconductor from the normal region can be reflected back as a hole, a process that transfers a Cooper pair into the superconducting condensate. In a short junction, each conduction channel supports a pair of such bound states. Those pairs can be represented as two-level systems with energy splittings controlled by the channel transmission and by the superconducting phase difference across the junction.

Graphene matters because the number and transmission of conduction channels can be controlled through geometry and Fermi level. In the model, those channels become a collection of non-identical two-level systems. That is more complicated than the textbook Dicke model, which usually assumes identical emitters, but it is also more realistic for a nanodevice.

Where Floquet thinking enters the story

The paper is not branded as a Floquet paper in the narrow sense of deriving a full Floquet spectrum for a periodically driven Hamiltonian. But it sits squarely in the Floquet/quantum-energy neighborhood because charging is controlled by time-dependent couplings and resonant photon exchange. The device can be charged through a sudden switch-on of the inductive coupling, and the authors also discuss an equivalent protocol based on modulating the superconducting phase difference.

For readers of Floquet.ca, the central idea is familiar: when a quantum system is driven at a frequency that matches an internal transition, energy can be transferred selectively. Here the internal transitions are Andreev-state splittings, and the drive resource is the resonator field or the phase control of the junction. The authors identify both single-photon resonances, where one resonator photon matches an Andreev transition, and two-photon resonances, where two photons participate in the charging process.

That two-photon channel is especially important because prior work by Crescente, Carrega, Sassetti, and Ferraro had already shown that two-photon Dicke quantum batteries can support ultrafast charging. The new proposal brings that mechanism into a graphene Josephson-junction setting and adds circuit-specific terms that are absent from the simplest Dicke story.

The unusual ingredient: longitudinal coupling

In ordinary presentations of a Dicke battery, the charger field flips the two-level systems from ground to excited states. In the Josephson-junction circuit, the coupling between resonator flux and junction supercurrent produces additional longitudinal interaction terms. These terms do not simply flip the two-level systems; they modify the dynamics in a way tied to the current-phase relation of the junction.

The authors find that these extra terms can be helpful or disruptive depending on the regime. Near a two-photon resonance, they can enhance the stored energy for the relevant Andreev-state subset. Near a single-photon resonance, the same terms can disturb the resonant contribution, although off-resonant two-photon contributions may partly compensate at stronger coupling.

The circuit does not merely implement a textbook Dicke battery. Its Josephson physics adds new knobs—and new complications—that could be useful if they are deliberately engineered.

This is a good example of why quantum-energy hardware cannot be judged only by abstract scaling laws. Real devices bring asymmetries, non-identical transitions, longitudinal couplings, leakage channels, and control constraints. Sometimes those imperfections are liabilities. Sometimes they are the source of the useful effect.

What would make this experimentally plausible?

Several pieces of the proposal have independent experimental support. Circuit QED with superconducting weak links has matured considerably, as reviewed in the broader superconducting-circuit literature by Krantz and colleagues and by Xiang, Ashhab, You, and Nori. Andreev bound states have been coherently manipulated in superconducting atomic contacts, including the 2015 Science experiment by Janvier and collaborators. Graphene Josephson junctions have also shown phase-dependent microwave responses, as in work by Haller and colleagues published in Physical Review Research in 2022. More recently, planar Josephson junctions based on semiconductor materials have been probed by direct microwave spectroscopy of Andreev bound states.

None of that means the full quantum battery has been built. It does mean the proposal is not floating free from experimental reality. The platform borrows from technologies that already know how to couple junctions to resonators, tune phases with flux, and resolve microwave transitions.

What still has to be proven

• Coherent storage: the stored energy must remain usable long enough to matter, despite relaxation, quasiparticles, dephasing, and disorder.
• Controlled charging: a lab would need to show selective population of the intended Andreev states through the resonator or phase modulation.
• Extractable work: high stored energy is not identical to useful work. A discharge protocol and ergotropy accounting are essential.
• Scaling: adding more channels or junctions should improve performance without simply adding noise and fabrication variation.

Why this matters for practical quantum energy

The most realistic near-term application of a quantum battery is not grid storage. It is local power management for quantum technologies. A superconducting sensor, a small processor module, or a cryogenic quantum device may benefit from integrated energy reservoirs that can be charged quickly and discharged coherently into nearby degrees of freedom. In that context, a graphene Josephson-junction battery is interesting because it lives in the same ecosystem as superconducting control hardware.

The proposal also gives Floquet engineers a new design playground. Phase modulation across the junction is effectively a time-dependent control handle. Resonator photons create frequency-selective transitions. Gate voltage and geometry tune the Andreev spectrum. Together, those knobs invite optimization: choosing the phase, drive timing, coupling strength, and channel distribution to maximize useful stored energy while limiting unwanted heating.

That makes the paper part of a broader shift in the field. Quantum batteries are moving from “can collective quantum effects boost charging?” toward “which physical platforms give us tunable spectra, measurable energy, and realistic control?” The answer may not be one universal architecture. It may be a family of device-specific batteries, each suited to a particular quantum technology stack.

The takeaway

Varrica and colleagues have proposed a compact, solid-state quantum battery architecture in which a two-dimensional-material Josephson junction supplies the storage medium and a superconducting resonator supplies the charger. In graphene, Andreev bound states act as non-identical two-level systems; the superconducting phase and device parameters tune their energy splittings; and both single-photon and two-photon resonant charging channels appear naturally.

The most intriguing feature is not simply that graphene can host a quantum battery. It is that Josephson physics enriches the standard Dicke-battery model with longitudinal couplings and phase-controlled protocols. If future experiments can demonstrate coherent charging, storage, and extractable work in such junctions, quantum batteries will have taken another step from abstract resource theory toward engineered quantum hardware.

For now, the result is best read as a high-quality design study: careful, platform-aware, and relevant to the long path from Floquet control to practical quantum energy devices.

Selected sources

• V. Varrica, G. Gemme, F. M. D. Pellegrino, E. Paladino, M. Sassetti, and D. Ferraro, “Quantum Batteries in two-dimensional material-based Josephson Junctions,” arXiv:2605.22582, submitted May 21, 2026.
• D. Ferraro, M. Campisi, G. M. Andolina, V. Pellegrini, and M. Polini, “High-Power Collective Charging of a Solid-State Quantum Battery,” Physical Review Letters 120, 117702 (2018).
• J. Q. Quach et al., “Superabsorption in an organic microcavity: Toward a quantum battery,” Science Advances 8, eabk3160 (2022).
• F. Campaioli, S. Gherardini, J. Q. Quach, M. Polini, and G. M. Andolina, “Colloquium: Quantum batteries,” Reviews of Modern Physics 96, 031001 (2024).
• R. Haller et al., “Phase-dependent microwave response of a graphene Josephson junction,” Physical Review Research 4, 013198 (2022).