Quantifying Trapped Magnetic Vortex Losses in Niobium Resonators at mK Temperatures

Conference · Thu Dec 04 04:00:00 EST 2025 · No journal information

DOI:https://doi.org/10.2172/3008673· OSTI ID:3008673

Bafia, Daniel P. ^[1]; Abdisatarov, Bektur ^[2]; Pilipenko, Roman ^[1]; Lu, Yao ^[1]; Eremeev, Grigory V. ^[1]; Romanenko, Alexander S. ^[1]; Grassellino, Anna ^[1]

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1. Fermilab
2. Fermilab; Old Dominion U.

Trapped magnetic vortices in niobium introduce microwave losses that degrade the performance of superconducting resonators. While such losses have been extensively studied above 1 K, we report here their direct quantification in the millikelvin and low-photon regime relevant to quantum devices. Using a high-quality factor 3D niobium cavity cooled through its superconducting transition in controlled magnetic fields, we isolate vortex-induced losses and find the resistive component of the sensitivity to trapped flux S to be approximately 2 nOhm/mG at 10 mK and 6 GHz. The decay rate is initially dominated by two-level system (TLS) losses from the native niobium pentoxide, with vortex-induced degradation of T1 occurring above Btrap~50 mG. In the absence of the oxide, even 10 mG of trapped flux limits performance, Q0 ~ 1010, or T1 ~350 ms, underscoring the need for stringent magnetic shielding. The resistive sensitivity, S, decreases with temperature and remains largely field-independent, whereas the reactive component, S , exhibits a maximum near 0.8 K. These behaviors are well modeled within the Coffey Clem framework in the zero-creep limit, under the assumption that vortex pinning is enhanced by thermally activated processes. Our results suggest that niobium-based transmon qubits can tolerate vortex-induced dissipation at trapped field levels up to several hundred mG, but achieving long coherence times still requires careful magnetic shielding to suppress lower-field losses from other mechanisms

• Research Organization: Old Dominion U.; Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: US Department of Energy
• DOE Contract Number: 89243024CSC000002
• OSTI ID: 3008673
• Report Number(s): FERMILAB-POSTER-25-0267-SQMS; oai:inspirehep.net:3093125
• Resource Type: Conference poster
• Conference Information: Journal Name: No journal information
• Country of Publication: United States
• Language: English