Noise limits for dc SQUID readout of high-$Q$ resonators below 300 MHz
V. Ankel, C. Bartram, J. Begin, C. Bell, L. Brouwer, S. Chaudhuri, John Clarke, H. -M. Cho, J. Corbin, W. Craddock, S. Cuadra, A. Droster, M. Durkin, J. Echevers, J. T. Fry, G. Hilton, K. D. Irwin, A. Keller, R. Kolevatov, A. Kunder, D. Li, N. Otto, K. M. W. Pappas, N. M. Rapidis, C. P. Salemi, D. Schmidt, M. Simanovskaia, J. Singh, P. Stark, C. D. Tesche, J. Ullom, L. Vale, E. C. van Assendelft, K. van Bibber, M. Vissers, K. Wells, J. Wiedemann, L. Winslow, D. Wright, A. K. Yi, B. A. Young
Published: 2025/4/29
Abstract
We present the limits on noise for the readout of cryogenic high-$Q$ resonators using dc Superconducting Quantum Interference Devices (SQUIDs) below 300 MHz. This analysis uses realized first-stage SQUIDs (previously published), whose performance is well described by Tesche-Clarke (TC) theory, coupled directly to the resonators. We also present data from a prototype second-stage dc SQUID array designed to couple to this first-stage SQUID as a follow-on amplifier with high system bandwidth. This analysis is the first full consideration of dc SQUID noise performance referred to a high-$Q$ resonator over this frequency range, and is presented relative to the standard quantum limit. We include imprecision, backaction, and backaction-imprecision noise correlations from TC theory, the noise contributed by the second-stage SQUIDs, wiring, and preamplifiers, and optimizations for both on-resonance measurements and off-resonance scan sensitivity. This architecture has modern relevance due to the increased interest in axion searches and the requirements of the DMRadio-m$^3$ axion search, which will use dc SQUIDs in this frequency range.