Two-level systems in superconducting quantum devices due to trapped quasiparticles
Artikel i vetenskaplig tidskrift, 2020

A major issue for the implementation of large-scale superconducting quantum circuits is the interaction with interfacial two-level system (TLS) defects that lead to qubit parameter fluctuations and relaxation. Another major challenge comes from nonequilibrium quasiparticles (QPs) that result in qubit relaxation and dephasing. Here, we reveal a previously unexplored decoherence mechanism in the form of a new type of TLS originating from trapped QPs, which can induce qubit relaxation. Using spectral, temporal, thermal, and magnetic field mapping of TLS-induced fluctuations in frequency tunable resonators, we identify a highly coherent subset of the general TLS population with a low reconfiguration temperature similar to 300 mK and a nonuniform density of states. These properties can be understood if the TLS are formed by QPs trapped in shallow subgap states formed by spatial fluctutations of the superconducting order parameter. This implies that even very rare QP bursts will affect coherence over exponentially long time scales.


S. E. de Graaf

National Physical Laboratory (NPL)

L. Faoro

Sorbonne Université

University of Wisconsin Madison

L. B. Ioffe

Google Inc.

University of Wisconsin Madison

Sumedh Mahashabde

Chalmers, Mikroteknologi och nanovetenskap, Kvantkomponentfysik

J. J. Burnett

National Physical Laboratory (NPL)

T. Lindstrom

National Physical Laboratory (NPL)

Sergey Kubatkin

Chalmers, Mikroteknologi och nanovetenskap, Kvantkomponentfysik

Andrey Danilov

Chalmers, Mikroteknologi och nanovetenskap, Kvantkomponentfysik

A. Ya Tzalenchuk

Royal Holloway University of London

National Physical Laboratory (NPL)

Science advances

2375-2548 (eISSN)

Vol. 6 51 eabc5055


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