Two-level systems in superconducting quantum devices due to trapped quasiparticles

• URL: http://arxiv.org/abs/2004.02485v1
• Date: Mon, 6 Apr 2020 08:38:28 GMT
• Title: Two-level systems in superconducting quantum devices due to trapped quasiparticles
• Authors: S. E. de Graaf, L. Faoro, L. B. Ioffe, S. Mahashabde, J. J. Burnett, T. Lindstr\"om, S. E. Kubatkin, A. V. Danilov and A. Ya. Tzalenchuk
• Abstract summary: We show that non-equilibrium quasiparticles can induce qubit relaxation in superconducting quantum circuits. Our results imply that trapped QPs can induce qubit relaxation.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: A major issue for the implementation of large scale superconducting quantum circuits is the interaction with interfacial two-level system defects (TLS) that leads to qubit relaxation and impedes qubit operation in certain frequency ranges that also drift in time. Another major challenge comes from non-equilibrium quasiparticles (QPs) that result in qubit dephasing and relaxation. In this work we show that such QPs can also serve as a source of TLS. Using spectral and temporal mapping of TLS-induced fluctuations in frequency tunable resonators, we identify a subset of the general TLS population that are highly coherent TLS with a low reconfiguration temperature $\sim$ 300 mK, and a non-uniform density of states. These properties can be understood if these TLS are formed by QPs trapped in shallow subgap states formed by spatial fluctutations of the superconducting order parameter $\Delta$. Magnetic field measurements of one such TLS reveals a link to superconductivity. Our results imply that trapped QPs can induce qubit relaxation.

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