Pound-Drever-Hall Measurement Through Simultaneous Heterodyne: Applications to Superconducting Qubits and RAM Suppression

Precise and long-term stable measurements of the phases of AC signals underly quantum technologies across the board, from atomic clocks to superconducting quantum processors. In this talk, we present two new applications of the Pound-Drever-Hall (PDH) method made possible through simultaneous heterodyne detection of the carrier and two sideband tones. First, experimental realization of a scalable and ultrastable readout technique for superconducting qubits based on PDH, which is highly robust against microwave phase drift, achieving a phase stability of 0.73 degrees over 2 hours, and capable of single-shot readout in the presence of phase errors exceeding the qubit-induced phase shift [1].  Second, a more general version of the standard PDH method, which we term the “scissors” phase. We show that the microwave scissors phase enables superconducting-qubit readout even in the presence of timing errors [1], and optical-frequency scissors phase produces an error signal which is insensitive to amplitude imbalance between the PDH sidebands (RAM). Our results establish a new class of PDH-based techniques, offering immediate applications to precision microwave measurement, superconducting quantum computing, and passive stability of optical oscillators.

 

[1] I. Adisa, W. C. Lee, K. C. Cox, and A. J. Kollár, arXiv preprint arXiv:2512.03138 (2025).