Pound–Drever–Hall-Based Spectroscopy of Multi-Mode Surface Acoustic Wave Resonators

We present spectroscopic measurements based on the Pound-Drever-Hall (PDH) technique to characterize a microwave-frequency (GHz) surface acoustic wave (SAW) resonator. The multi-mode acoustic resonator is integrated in a notch-type measurement geometry and fabricated on Y-cut lithium niobate. We measure the single-frequency amplitude and phase of the resonator’s response as well as the PDH observable. We find that PDH can be used to identify both the primary resonant modes of the device as well as spurious substrate modes that are difficult to detect with conventional methods. We demonstrate that PDH is insensitive to phase errors and can be used to eliminate these spurious acoustic signals and background frequency drift (see the presentation in Ref. [1] for details on the PDH measurement technique). Finally, we discuss how this type of measurement could be utilized to develop SAW-based quantum sensors, particularly when integrated with superconducting qubits.

[1] J.D. Philips et al., Improved microwave resonator measurements using Pound-Drever-Hall sensing, APS Global Physics Summit 2026 (this meeting).