Magneto-Optic Modulator with Unit Quantum Efficiency

We propose a device for the reversible and quiet conversion of microwave photons to optical sideband photons, that can reach 100% quantum effciency. The device is based on an erbium doped crystal placed in both an optical and microwave resonator. We show that effcient conversion can be achieved so long as the product of the optical and microwave cooperativity factors can be made large. We argue achieving this regime is feasible with current technology and we discuss a possible implementation.