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WEIAA01 
The Frequency Shift and Q of Disordered Superconducting RF Cavities  


Funding: U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under contract No. DEAC0207CH11359. Superconducting RF (SRF) cavity resonators with ultrahighQ, originally developed for particle accelerator technology, are a key technology platform for detectors of rare events, e.g. light by light scattering mediated by virtual electronpositron pairs, axions [1] and highfrequency gravitational waves [2]. The mechanism(s) leading to current limits in Q are not fully understood. We developed a numerical method to calculate Q and cavity resonant frequency shifts based on nonequilibrium theory of superconductivity, including the role of impurity disorder, combined with Slater’s method for solving Maxwell’s equations for the EM field confined in a cavity [3]. Our results for the frequency shift and Q are in excellent agreement with experimental data reported by the SRF group at Fermilab [4]. As a measure of the predictive capability of the theory we are able to quantitatively account for changes in the resonant frequency of order 10 Hz for GHz SRF cavities over temperature ranges of 0.001 Tc. This level of predictive theory is essential for further improvements in performance of superconducting resonators and devices for quantum sensing and quantum processors. [1] Z. Bogorad et al., Phys. Rev. Lett. 123, 021801 (2019). [2] A. Berlin et al., arXiv:2303.0151. [3] H. Ueki, M. Zarea, and J. A. Sauls, arXiv:2207.14236. [4] D. Bafia et al., arXiv:2103.10601. 

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