Coherent dynamics and dissipation in a phononic open quantum system

Circuit quantum acoustodynamics (cQAD) enables the investigation of the fundamental quantum properties of phonons by experimentally leveraging the intrinsic nonlinearity of superconducting qubits. Here we describe an experiment in which the electro-mechanical response of a piezoelectric surface acoustic wave (SAW) device enables the realization of a phononic open quantum system that simultaneously samples both the strong and weakly coupled regimes of cQAD. This system is experimentally realized via capacitive coupling between a transmon qubit and a custom-designed SAW resonator. Using the coupling-of-modes method we model the electro-mechanical properties of the SAW and are able to create a spectrum of SAW phonons that includes a confined surface phonon mode that is strongly coupled to the qubit along with a quasi-continuum of lossy modes that exit the phonon resonator.