Coherent Optical Coupling to Surface Acoustic Wave Devices

Surface acoustic waves (SAW) and associated SAW devices are ideal for sensing, metrology, and connecting and controlling hybrid quantum devices. While the advances demonstrated to date are largely based on electromechanical coupling, a robust and customizable coherent optical coupling would unlock mature and powerful cavity optomechanical control techniques and an efficient optical pathway for long-distance quantum links. Here we demonstrate direct and robust coherent optical coupling to surface acoustic wave cavities through a Brillouin-like optomechanical interaction. In high-frequency SAW cavities designed with curved metallic acoustic reflectors deposited on crystalline substrates, SAW modes are efficiently optically accessed in piezo-active directions that can be accessed through traditionally electromechanical techniques as well as non-piezo-active directions that cannot. The non-contact nature of the optical technique enables controlled analysis of dissipation mechanisms and access to pristine mechanical resonators with record-level quality factors (>100,000 measured here). The exceptional control of the optical probe beams also enables detailed transverse spatial mode spectroscopy, for the first time. These advantages combined with simple fabrication, small size, large power handling, and strong coupling to quantum systems make SAW optomechanical platforms particularly attractive for sensing, material science, and hybrid quantum systems.