Microwave-to-optical conversion via four-wave mixing in a cold ytterbium ensemble

Interfacing superconducting qubits with optical photons require noise-free microwave-to-optical transducers, a technology currently not realized at the single-photon level. We propose to use four-wave mixing in an ensemble of cold ytterbium (Yb) atoms prepared in the metastable ``clock'' state. The parametric process uses two high-lying Rydberg states for bidirectional conversion between a 10 GHz microwave photon and an optical photon in the telecommunication E-band. To avoid noise photons due to spontaneous emission, we consider continuous operation far detuned from the intermediate states. We use an input-output formalism to predict conversion efficiencies of ≈50% with bandwidths of ≈100 kHz.