Off-Resonant, Free-Space Launching of High-Frequency Surface Acoustic Waves*

Piezoelectric surface acoustic wave (SAW) devices operating in the GHz-frequency range find application in a wide variety of classical microwave telecom circuits including, SAW filters, resonators, and sensors. SAWs have also been of increasing interest in the development of hybrid quantum systems containing superconducting circuits and qubits, providing insight into the regime of circuit quantum acoustodynamics (cQAD). Here we report on experiments demonstrating the off-resonant free-space coupling between the dipole moment of a SAW resonator and a mode of a three-dimensional (3D) microwave cavity that is detuned by approximately 0.4 GHz from the main SAW resonance. We find that this response is well described by a coupling of modes modeling of the SAW resonator. These results reveal how the intrinsically large impedance mismatch between the SAW and electromagnetic resonators can be overcome via the fabrication of large antenna pads on a strong piezoelectric substrate (lithium niobate) and how these devices can be incorporated into novel cQAD systems.