Coherent, focusing surface acoustic wave resonators for multimode quantum acoustodynamics*

Acoustic platforms offer quantum technologies a promising combination of competitive coherence times, long on-chip delays, and the ability to connect disparate quantum systems. Surface acoustic wave (SAW) devices are particularly adept at leveraging these delays to realize high-performance and designable filters. Experiments combining SAW devices with superconducting qubits have required a trade-off between the anharmonicity of the qubit and the width of the acoustic aperture, resulting in significant acoustic losses to diffraction in typical flat geometries. Here, we demonstrate highly coherent (Q >3x10⁵) SAW resonators on quartz with narrow apertures (aperture < 5λ) by using curved reflectors to form stable cavities, a design task complicated by the anisotropy of sound on quartz. These resonators are poised for integration with superconducting qubits to create devices able to investigate quantum acoustodynamics in the multi-mode, strong dispersive regime.