Adaptive Spectroscopy of Fast Two-Level-System Dynamics in Superconducting Qubits

  1. Fabrizio Berritta,
  2. David Pahl,
  3. Lukas Pahl,
  4. William P. Banner,
  5. Gabriel Cutter,
  6. Jan A. Krzywda,
  7. Spencer Weeden,
  8. Shravan Patel,
  9. Paul Buttles,
  10. Stanislav Eilhart,
  11. Michael Gingras,
  12. Bethany M. Niedzielski,
  13. Robert McDermott,
  14. Mollie E. Schwartz,
  15. Kyle Serniak,
  16. Max Hays,
  17. Jeffrey A. Grover,
  18. and William D. Oliver
Parasitic two-level-system (TLS) defects are a major source of energy relaxation and temporal instability in superconducting quantum processors. Our sub-second adaptive spectroscopy reveals telegraphic switching of TLSs with a characteristic timescale of a few seconds and spectral diffusion with diffusivity D≈0.9 MHz2/s. These timescales are about 3×102 times faster than what is observed in conventional nonadaptive spectroscopy, which typically requires hours of measurement time. We resolve such fast dynamics on a field-programmable gate array (FPGA)-based controller that enables measurement of frequency- and time-resolved relaxations with sub-second temporal resolution in flux-tunable superconducting qubits. We observe similar defect dynamics across multiple qubits in independently fabricated devices measured in different laboratories. We correlate TLS-induced fluctuations with gate-level errors using randomized benchmarking. Our results reveal a previously inaccessible regime of frequency-resolved TLS dynamics and redefine the timescales relevant to TLS-aware characterization and calibration of superconducting quantum processors.
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