Measurement of energy decay in superconducting qubits from nonequilibrium quasiparticles

M. Lenander, H. Wang, Radoslaw C. Bialczak, Erik Lucero, Matteo Mariantoni, M. Neeley, A. D. O’Connell, D. Sank, M. Weides, J. Wenner, T. Yamamoto, Y. Yin, J. Zhao, A. N. Cleland, and John M. Martinis
Phys. Rev. B 84, 024501 – Published 1 July 2011

Abstract

Quasiparticles are an important decoherence mechanism in superconducting qubits, and can be described with a complex admittance that is a generalization of the Mattis-Bardeen theory. By injecting nonequilibrium quasiparticles with a tunnel junction, we verify qualitatively the expected change of the decay rate and transition frequency in a phase qubit. With their relative change in agreement to within 4 % of prediction, the theory can be reliably used to infer quasiparticle density. We describe how settling of the decay rate may allow determination of whether qubit energy relaxation is limited by nonequilibrium quasiparticles.

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  • Received 3 January 2011

DOI:https://doi.org/10.1103/PhysRevB.84.024501

©2011 American Physical Society

Authors & Affiliations

M. Lenander1, H. Wang1,2, Radoslaw C. Bialczak1, Erik Lucero1, Matteo Mariantoni1, M. Neeley1, A. D. O’Connell1, D. Sank1, M. Weides1, J. Wenner1, T. Yamamoto1,3, Y. Yin1, J. Zhao1, A. N. Cleland1, and John M. Martinis1

  • 1Department of Physics, University of California, Santa Barbara, California 93106, USA
  • 2Department of Physics, Zhejiang University, Hangzhou 310027, China
  • 3Green Innovation Research Laboratories, NEC Corporation, Tsukuba, Ibaraki 305-8501, Japan

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Vol. 84, Iss. 2 — 1 July 2011

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