Characterization and Comparison of Energy Relaxation in Fluxonium Qubits
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2026
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| author | Azar, Kate Ateshian, Lamia Randeria, Mallika T. Piñero, Renée DePencier Gertler, Jeffrey M. An, Junyoung Contipelli, Felipe Ding, Leon Gingras, Michael Grossklaus, Kevin Hays, Max Hazard, Thomas M. Kim, Junghyun Niedzielski, Bethany M. Stickler, Hannah Tiwari, Kunal L. Zhang, Helin Grover, Jeffrey A. Yoder, Jonilyn L. Schwartz, Mollie E. Oliver, William D. Serniak, Kyle |
| author_facet | Azar, Kate Ateshian, Lamia Randeria, Mallika T. Piñero, Renée DePencier Gertler, Jeffrey M. An, Junyoung Contipelli, Felipe Ding, Leon Gingras, Michael Grossklaus, Kevin Hays, Max Hazard, Thomas M. Kim, Junghyun Niedzielski, Bethany M. Stickler, Hannah Tiwari, Kunal L. Zhang, Helin Grover, Jeffrey A. Yoder, Jonilyn L. Schwartz, Mollie E. Oliver, William D. Serniak, Kyle |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_23636 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Characterization and Comparison of Energy Relaxation in Fluxonium Qubits Azar, Kate Ateshian, Lamia Randeria, Mallika T. Piñero, Renée DePencier Gertler, Jeffrey M. An, Junyoung Contipelli, Felipe Ding, Leon Gingras, Michael Grossklaus, Kevin Hays, Max Hazard, Thomas M. Kim, Junghyun Niedzielski, Bethany M. Stickler, Hannah Tiwari, Kunal L. Zhang, Helin Grover, Jeffrey A. Yoder, Jonilyn L. Schwartz, Mollie E. Oliver, William D. Serniak, Kyle Quantum Physics Mesoscale and Nanoscale Physics 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. |
| title | Characterization and Comparison of Energy Relaxation in Fluxonium Qubits |
| topic | Quantum Physics Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2603.23636 |