Microwave-optical photon correlations in a piezo-optomechanical quantum transducer

We operate a piezo-optomechanical transducer in a parametric down-conversion scheme geared to generate entangled microwave-optical photon pairs. In this scheme, an optical pump first generates entangled optical photons and phonons in pairs via radiation pressure. Subsequently, a strong piezoelectric interaction converts the phonon into a microwave photon with high efficiency. Crucially, during this sequence, we can maintain optical pump induced noise in the circuit well below one quantum. High repetition rate and efficient readout allow us to detect a large intensity correlation between microwave and optical fields, nearly twice the value for thermal states. We outline a scheme to utilize these correlations for optically heralded entanglement generation between remote superconducting qubits.