We develop a high speed on-chip flux measurement using a capacitively shunted SQUID as an embedded cryogenic transducer and apply this technique to the qualification of a near-term scalable printed circuit board (PCB) package for frequency tunable superconducting qubits. The transducer is a flux tunable LC resonator where applied flux changes the resonant frequency. We apply a microwave tone to probe this frequency and use a time-domain homodyne measurement to extract the reflected phase as a function of flux applied to the SQUID. The transducer response bandwidth is 2.6 GHz with a maximum gain of 1200∘/Φ0 allowing us to study the settling amplitude to better than 0.1%. We use this technique to characterize on-chip bias line routing and a variety of PCB based packages and demonstrate that step response settling can vary by orders of magnitude in both settling time and amplitude depending on if normal or superconducting materials are used. By plating copper PCBs in aluminum we measure a step response consistent with the packaging used for existing high-fidelity qubits.
@article{arxiv.1808.09612,
title = {High speed flux sampling for tunable superconducting qubits with an embedded cryogenic transducer},
author = {B. Foxen and J. Y. Mutus and E. Lucero and E. Jeffrey and D. Sank and R. Barends and K. Arya and B. Burkett and Yu Chen and Zijun Chen and B. Chiaro and A. Dunsworth and A. Fowler and C. Gidney and M. Giustina and R. Graff and T. Huang and J. Kelly and P. Klimov and A. Megrant and O. Naaman and M. Neeley and C. Neill and C. Quintana and P. Roushan and A. Vainsencher and J. Wenner and T. C. White and John M. Martinis},
journal= {arXiv preprint arXiv:1808.09612},
year = {2020}
}