Rapid characterization of superconducting microwave resonators using thePound-Drever-Hall technique

As superconducting qubit coherence times reach an upper bound set by coupling to two-

level system defects in amorphous dielectric substrates, rapid material loss characterization

is needed to achieve significant improvement [1]. Power scans of superconducting microwave

resonators are commonly used to distinguish between loss channels induced in superconduct-

ing qubits and other ancillary low-power superconducting devices, but the standard method

of measurement using a simple vector network analyzer (VNA) frequency sweep is inefficient

and slow — a full characterization of a single device takes days due to the very low power

levels required. The Pound-Drever-Hall (PDH) technique, however, can extract the relevant

resonator parameters in a fraction of the time [2, 3]. By sending a carrier signal at the

resonant frequency and frequency modulation sidebands, then measuring power to generate

cross terms, one can create an error signal with a zero crossing exactly at the resonant fre-

quency. A PID controller adjusts the carrier signal until its frequency matches the resonant

frequency. The signal demodulated at twice the modulation frequency is strongly sensitive to

Q, and therefore can be used to measure the loss tangent [3]. Additionally, low power noise

studies of resonators become accessible [4]. In this talk, we demonstrate fast characterization

of TLS loss and show a direct comparison of this technique with the conventional method of

using a VNA.

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T. Brecht, A. Dunsworth, D. P. Pappas, and J. Mutus,

Materials loss measurements using superconducting mi-

crowave resonators, Review of Scientific Instruments 91,

091101 (2020), https://doi.org/10.1063/5.0017378.

[2] T. Lindstr ¨om, J. Burnett, M. Oxborrow, and A. Y. Tza-

lenchuk, Pound-locking for characterization of supercon-

ducting microresonators, Review of Scientific Instruments

82, 104706 (2011), https://doi.org/10.1063/1.3648134.

[3] S. E. de Graaf, A. V. Danilov, and S. E. Kubatkin, Ac-

curate real-time monitoring of quality factor and center

frequency of superconducting resonators, IEEE Transac-

tions on Applied Superconductivity 24, 1 (2014).

[4] J. Burnett, High precision readout of superconducting res-

onators: For analysis of slow noise processes, Ph.D. thesis

(2014).