Coupling of transmon qubits to ultra-high Q phononic bandgap acoustic resonators via an intermediate piezoelectric resonator

We present the design, fabrication, and initial characterization of a superconducting transmon qubit coupled to an ultra-high quality (Q>10 billion) phononic crystal cavity, both of which are fabricated from the silicon device of a silicon-on-insulator wafer. In order to avoid the typically large material loss from piezoelectric materials, the qubit-phonon transducing device developed in this work is based on an engineered tunable piezoelectric virtual coupling channel involving an intermediate piezoelectric mechanical resonator hybridized with a tunable microwave resonator. The ability to achieve such a hybrid quantum system can enable new research paths towards a compact on-chip quantum memory element, mechanical quantum state manipulation, and quantum transduction between microwave and optical signals.