Investigation of coherence of niobium-based resonators enabled by a fast-sealing microwave cavity

Quantum Physics [Submitted on 9 Apr 2026] Investigation of coherence of niobium-based resonators enabled by a fast-sealing microwave cavity Chi Zhang, Richard Germond, Noah Janzen, Anne-Marie Valente-Feliciano, Mustafa Bal, Adrian Lupascu Resonators and qubits with a niobium (Nb) base metal layer achieve some of the highest coherence times in superconducting quantum devices. The performance of such devices is often limited by loss associated with two-level systems, which are found primarily at material surfaces and interfaces. The metal-air (MA) interface is a major contributor to device loss. In this work, we develop a fast-sealing microwave cavity that enables devices to be placed under vacuum within five minutes of oxide removal, thereby significantly reducing the MA interface loss compared to common device processing and packaging approaches. Using coplanar stripline resonators, we demonstrate that devices sealed in such a cavity exhibit internal quality factors exceeding one million at single-photon power. After re-exposure to air, the devices show downward resonance frequency shifts and quality factor degradations, quantitatively consistent with a model of Nb oxide regrowth. The fast-sealing microwave cavity provides a practical and consistent method to mitigate MA interface loss and sustain high coherence in Nb devices, and establishes a controlled platform for studying metal oxide regrowth kinetics and dielectric properties, the understanding of which is critical to achieving high coherence in superconducting quantum devices. Comments: 7 pages, 4 figures Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2604.08813 [quant-ph]   (or arXiv:2604.08813v1 [quant-ph] for this version)   https://doi.org/10.48550/arXiv.2604.08813 Focus to learn more Submission history From: Chi Zhang [view email] [v1] Thu, 9 Apr 2026 23:07:47 UTC (10,853 KB) Access Paper: HTML (experimental) view license Current browse context: quant-ph < prev   |   next > new | recent | 2026-04 References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)