High impedance NbN resonators for piezo-optomechanical microwave to optical quantum transducers - Part 1

Microwave-to-optical quantum transducers could enable large-scale quantum networking of superconducting quantum processors. The performance of such quantum transducers developed to date, however, is still far from the efficiency and noise level that would make this practical. Integrated piezo-optomechanical systems are a promising device technology for microwave-to-optical transduction. Nevertheless, current realizations are limited by optical absorption in the superconducting circuit. Motivated by fast quasiparticle relaxation in niobium nitride (NbN), we develop a process to integrate high impedance NbN resonators and silicon optomechanical crystals into a piezo-optomechanical transducer. We achieve high-Q microwave (1x10⁴), optical (1.5x10⁵) and acoustic (4x10⁴) modes in our NbN on silicon-on-insulator (SOI) platform. Our microwave resonator design provides 10% frequency tunability, essential for resonant interaction with acoustic modes. Further, the high impedance of ~10kΩ allows a transducer design with reduced piezo volume, and is expected to provide a 10x improvement in intrinsic transduction efficiency.