A Cavity-Magnon Transducer Linking Microwave and Optical Carriers

Quantum networks face a carrier mismatch: processing happens at microwave frequencies in superconducting circuits, while transmission happens at optical frequencies in fibre. A transducer that converts between the two coherently is the missing component. This paper designs one around the magnon mode of a ferrimagnetic sphere coupled to both a microwave cavity and an optical cavity, and computes its conversion performance. The microwave cooperativity is 250 and the optical cooperativity 180, giving a computed internal conversion efficiency whose external value is 77.5 percent. Efficiencies of this class make the transducer usable for heralded state transfer, where low efficiency costs rate rather than fidelity. The device is a design study; nothing has been fabricated or measured.