Characterization and Comparison of Energy Relaxation in Fluxonium Qubits

Quantum Physics [Submitted on 24 Mar 2026] Characterization and Comparison of Energy Relaxation in Fluxonium Qubits Kate Azar, Lamia Ateshian, Mallika T. Randeria, Renée DePencier Piñero, Jeffrey M. Gertler, Junyoung An, Felipe Contipelli, Leon Ding, Michael Gingras, Kevin Grossklaus, Max Hays, Thomas M. Hazard, Junghyun Kim, Bethany M. Niedzielski, Hannah Stickler, Kunal L. Tiwari, Helin Zhang, Jeffrey A. Grover, Jonilyn L. Yoder, Mollie E. Schwartz, William D. Oliver, Kyle Serniak Fluxonium superconducting qubits have demonstrated long coherence times and high single- and two-qubit gate fidelities, making them a favorable building block for superconducting quantum processors. We investigate the dominant limitations to fluxonium qubit energy relaxation time T_1 using a set of eight planar, aluminum-on-silicon qubits. We find that a circuit-based model for capacitive dielectric loss best captures the frequency dependence of T_1, which we analyze within both a two-level and a six-level energy relaxation model. We convert the measured T_1 into an effective capacitive quality factor Q_\mathrm{C}^{\mathrm{eff}} to compare qubits on equal footing, accounting for independently estimated contributions from 1/f flux noise and radiative loss to the control and readout circuitry. We apply this methodology to compare qubits from two fabrication processes: a baseline process and one that applies a fluorine-based wet treatment prior to Josephson junction deposition. We resolve a small improvement of (13.8 \pm 8.4)\% in the process mean Q_\mathrm{C}^{\mathrm{eff}}, indicating that the fluorine treatment may have reduced loss from the metal-substrate interface, but did not address the primary source of loss in these fluxonium qubits. Comments: 25 pages, 20 figures Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall) Cite as: arXiv:2603.23636 [quant-ph]   (or arXiv:2603.23636v1 [quant-ph] for this version)   https://doi.org/10.48550/arXiv.2603.23636 Focus to learn more Submission history From: Kate Azar [view email] [v1] Tue, 24 Mar 2026 18:21:42 UTC (14,180 KB) Access Paper: HTML (experimental) view license Current browse context: quant-ph < prev   |   next > new | recent | 2026-03 Change to browse by: cond-mat cond-mat.mes-hall 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?)