Microwave-to-optical transduction using magnon-exciton coupling.

Quantum networks require coherent interfaces between microwave-frequency quantum systems and low-loss optical links. However, existing microwave-optical transducers often trade conversion efficiency against added noise, bandwidth and device integrability. Here we use magnon-exciton coupling in the layered antiferromagnet CrSBr to realize coherent microwave-to-optical transduction. Unlike previous magnon-based approaches that rely on intrinsically weak off-resonant magneto-optical effects, our scheme exploits strong light-matter interactions at exciton resonances. Driving the antiferromagnetic resonance with microwaves modulates the resonant excitonic susceptibility and generates coherent optical sidebands, detected using homodyne interferometry. Even in a bulk crystal without cavity enhancement, we observe coherent conversion over an intrinsically broadband ~300-MHz window. Multiple exciton-polariton resonances inherit the magnon-coupled response, indicating a route to broaden the usable optical detuning range and mitigate optical dissipation. Magnon-coupled excitons in layered magnets thus offer a scalable platform for broadband microwave-optical interfaces, with higher cooperativity achievable through reduced magnetic volume and cavity integration.