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

S. E. de Graaf; L. Faoro; L. B. Ioffe; S. Mahashabde; J. J. Burnett; T. Lindström; S. E. Kubatkin; A. V. Danilov; A. Ya. Tzalenchuk

doi:10.1126/sciadv.abc5055

arXiv · 2004.02485

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

S. E. de Graaf·L. Faoro·L. B. Ioffe·S. Mahashabde·J. J. Burnett·T. Lindström·S. E. Kubatkin·A. V. Danilov·A. Ya. Tzalenchuk

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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 $Δ$. 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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S. E. de Graaf, L. Faoro, L. B. Ioffe, S. Mahashabde, J. J. Burnett, T. Lindström, S. E. Kubatkin, A. V. Danilov, A. Ya. Tzalenchuk. 2020-04-06. Two-level systems in superconducting quantum devices due to trapped quasiparticles. https://doi.org/10.1126/sciadv.abc5055

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