Flux Noise Spectroscopy Using Pound-Drever-Hall Tracking of a SQUID-Array based Resonator

Superconducting circuits are leading candidates for realizing quantum computers, but flux-tunable devices remain sensitive to magnetic-flux noise that induces drifts and dephasing. Reliable and rapid characterization of this noise is essential for improving device stability. We report a flux-noise spectroscopy technique based on a flux-tunable resonator composed of a DC SQUID array. Using Pound-Drever-Hall locking, we monitor the resonator frequency in real time and extract the flux noise power spectra. The device provides high sensitivity to magnetic fluctuations at the chip level, enabling detection of broadband background noise and discrete spurs. This approach establishes a compact tool for characterizing flux noise and guiding improvements in superconducting qubit environments.