High impedance NbN resonators for piezo-optomechanical microwave to optical quantum transducers - Part 2*

A chip-scale microwave (MW) to optical quantum transducer involves operation of a superconducting circuit in close proximity to an optical device carrying relatively high optical power. Towards a piezo-optomechanical transducer addressing this challenge, we study the performance of NbN high impedance resonators integrated with silicon optomechanical crystals (OMCs). Through MW testing of NbN resonators under optical pumping of the OMCs, we identify the relative strengths of various sources of scattered light. With our transducer geometry, we show sub-linewidth frequency shift and 0.4 added noise quanta in the MW resonator at a CW optical power corresponding to 900 intra-cavity photons in the OMC. This pump power is an order of magnitude above the level typically used to perform efficient phonon-photon transduction in our device, and is indicative of the robustness of the circuit to optical illumination. This is an important step towards a high repetition rate quantum transducer capable of bi-directional state transfer and entanglement generation between microwave and optical photons.