Capacitively Mediated Quantum Acoustic Strong Coupling in a Hybrid SAW-Qubit System*

Piezoelectric surface acoustic wave (SAW) devices can be integrated with superconducting qubits in a framework similar to circuit quantum electrodynamics known as circuit quantum acoustodynamics (cQAD). In these hybrid systems the intrinsic non-linearity of the superconducting qubit is leveraged to access new regimes of circuit quantum optics using GHz-frequency piezophonons. Here we present a cQAD architecture based on a purely capacitive coupling between a superconducting transmon qubit and a SAW resonator housed in a three-dimensional microwave cavity. This system achieves the strong coupling regime of cQAD with a coupling on the order of 10 MHz. The properties of the SAW resonator, as well as its impact on the transmon lifetime, are well-described by the coupling-of-modes formalism of SAW devices. Higher power microwave measurements reveal the presence of strongly non-linear (and non-classical) features of the spectroscopic response of the coupled system.