Oxygen Vacancies in Niobium Pentoxide as a Source of Two-Level System Losses in Superconducting Niobium
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arXiv
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| Auteurs principaux: | , , , |
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| Format: | Preprint |
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2021
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| _version_ | 1866910908551266304 |
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| author | Bafia, Daniel Murthy, Akshay Grassellino, Anna Romanenko, Alexander |
| author_facet | Bafia, Daniel Murthy, Akshay Grassellino, Anna Romanenko, Alexander |
| contents | We identify a major source of quantum decoherence in three-dimensional superconducting radio-frequency (SRF) resonators and two-dimensional transmon qubits composed of oxidized niobium: oxygen vacancies in the niobium pentoxide which drive two-level system (TLS) losses. By probing the effect of sequential \textit{in situ} vacuum baking treatments on the RF performance of bulk Nb SRF resonators and on the oxide structure of a representative Nb sample using time-of-flight secondary ion mass spectrometry (ToF-SIMS), we find a non-monotonic evolution of cavity quality factor $Q_0$ which correlates with the interplay of Nb\textsubscript{2}O\textsubscript{5} vacancy generation and oxide thickness reduction. We localize this effect to the oxide itself and present the insignificant role of diffused interstitial oxygen in the underlying Nb by regrowing a new oxide \textit{via} wet oxidation which reveals a mitigation of aggravated TLS losses. We hypothesize that such vacancies in the pentoxide serve as magnetic impurities and are a source of TLS-driven RF loss. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2108_13352 |
| institution | arXiv |
| publishDate | 2021 |
| record_format | arxiv |
| spellingShingle | Oxygen Vacancies in Niobium Pentoxide as a Source of Two-Level System Losses in Superconducting Niobium Bafia, Daniel Murthy, Akshay Grassellino, Anna Romanenko, Alexander Applied Physics Quantum Physics We identify a major source of quantum decoherence in three-dimensional superconducting radio-frequency (SRF) resonators and two-dimensional transmon qubits composed of oxidized niobium: oxygen vacancies in the niobium pentoxide which drive two-level system (TLS) losses. By probing the effect of sequential \textit{in situ} vacuum baking treatments on the RF performance of bulk Nb SRF resonators and on the oxide structure of a representative Nb sample using time-of-flight secondary ion mass spectrometry (ToF-SIMS), we find a non-monotonic evolution of cavity quality factor $Q_0$ which correlates with the interplay of Nb\textsubscript{2}O\textsubscript{5} vacancy generation and oxide thickness reduction. We localize this effect to the oxide itself and present the insignificant role of diffused interstitial oxygen in the underlying Nb by regrowing a new oxide \textit{via} wet oxidation which reveals a mitigation of aggravated TLS losses. We hypothesize that such vacancies in the pentoxide serve as magnetic impurities and are a source of TLS-driven RF loss. |
| title | Oxygen Vacancies in Niobium Pentoxide as a Source of Two-Level System Losses in Superconducting Niobium |
| topic | Applied Physics Quantum Physics |
| url | https://arxiv.org/abs/2108.13352 |