Quasiparticle-induced transitions in a fluxonium qubit

• URL: http://arxiv.org/abs/2607.21329v1
• Date: Thu, 23 Jul 2026 13:57:49 GMT
• Title: Quasiparticle-induced transitions in a fluxonium qubit
• Abstract summary: We measure the excitation and de-excitation rates in a fluxonium qubit under controlled on-chip quasiparticle injection.<n>We show that to accurately model the external magnetic flux dependence of the quasiparticle-induced transition rates, it is necessary to account for the superconducting gap asymmetry across the Josephson junctions.
• Score: 0.017239403798849817
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Quasiparticles are a prominent decoherence source in superconducting qubits, but their effects are notoriously difficult to isolate in fluxonium. Unlike a transmon, fluxonium is insensitive to offset charge, precluding charge-parity detection of quasiparticle tunneling. We address this challenge by measuring the excitation and de-excitation rates in a fluxonium qubit under controlled on-chip quasiparticle injection. We show that to accurately model the external magnetic flux dependence of the quasiparticle-induced transition rates, it is necessary to account for the superconducting gap asymmetry across the Josephson junctions. A comparison between theory and experiment constrains the relative quasiparticle contributions of the junction array and the small junction and helps explain previously reported discrepancies between the bounds on the quasiparticle densities inferred for these two circuit elements.

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