Paper | Title | Page |
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TUIBA01 | A Three-Fluid Model of Dissipation at Surfaces in Superconducting Radiofrequency Cavities | 361 |
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Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Experiments on superconducting cavities have found that under large RF fields the quality factor can improve with increasing field amplitude, a so-called anti-Q slope. We numerically solve the Bogoliubov-de Gennes equations at a superconducting surface in a parallel magnetic field, finding at large fields there are surface quasiparticle states with energies below the bulk superconducting gap that emerge and disappear as the field cycles. Modifying the standard two-fluid model, we introduce a ‘‘three’’-fluid model where we partition the normal fluid to consider continuum and surface quasiparticle states separately. We compute dissipation in a semi-classical theory of conductivity, where we provide physical estimates of elastic scattering times of Bogoliubov quasiparticles with point-like impurities having potential strengths informed from complementary ab initio calculations of impurities in bulk niobium. We show, in this simple yet effective framework, how the relative scattering rates of surface and continuum quasiparticle states can play a role in producing an anti-Q slope while demonstrating how this model naturally includes a mechanism for turning the anti-Q slope on and off. S. Deyo, M. Kelley et al. Phys. Rev. B 106, 104502 (2022) |
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Slides TUIBA01 [2.019 MB] | ||
DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUIBA01 | |
About • | Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 08 July 2023 | |
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TUIBA02 |
Vacancy Dynamics in Niobium and Its Native Oxides and Their Potential Implications for Quantum Computing and Superconducting Accelerators | |
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Funding: This work was supported by the BMBF under the research grants 05K19GUB and 05H2021. In recent years, superconducting radio-frequency (SRF) cavities have been considered as candidates for qubits in quantum computing, showing longer photon lifetimes and, therefore, longer decoherence times of a cavity stored qubit compared to many other realizations. In modern particle accelerators, SRF cavities are the workhorse. Continuous research and development efforts are being undertaken to improve their properties, i.e., to increase the accelerating field and lower the surface resistance, which in turn increase the energy reach and duty cycle of accelerators. While some experimental milestones have been achieved, the mechanisms behind the still observed losses remain not fully understood. This talk will show that a recently reported temperature treatment of Nb SRF cavities in the temperature range of 573-673 K, which reduces the residual surface resistance to unprecedented values, is linked to a reorganization of the niobium oxide and near-surface vacancy structure and that this reorganization can explain the observed improved performance in both applications, quantum computing and SRF cavities. |
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Slides TUIBA02 [2.352 MB] | ||
Cite • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |