Disentangling the sources of ionizing radiation in superconducting qubits

  1. L. Cardani,
  2. I. Colantoni,
  3. A. Cruciani,
  4. F. De Dominicis,
  5. G. D'Imperio,
  6. M. Laubenstein,
  7. A. Mariani,
  8. L. Pagnanini,
  9. S. Pirro,
  10. C. Tomei,
  11. N. Casali,
  12. F. Ferroni,
  13. D. Frolov,
  14. L. Gironi,
  15. A. Grassellino,
  16. M. Junker,
  17. C. Kopas,
  18. E. Lachman,
  19. C.R.H. McRae,
  20. J. Mutus,
  21. M. Nastasi,
  22. D. P. Pappas,
  23. R. Pilipenko,
  24. M. Sisti,
  25. V. Pettinacci,
  26. A. Romanenko,
  27. D. Van Zanten,
  28. M. Vignati,
  29. J. D. Withrow,
  30. and N. Z. Zhelev
Radioactivity was recently discovered as a source of decoherence and correlated errors for the real-world implementation of superconducting quantum processors. In this work, we measure
levels of radioactivity present in a typical laboratory environment (from muons, neutrons, and gamma’s emitted by naturally occurring radioactive isotopes) and in the most commonly used materials for the assembly and operation of state-of-the-art superconducting qubits. We develop a GEANT-4 based simulation to predict the rate of impacts and the amount of energy released in a qubit chip from each of the mentioned sources. We finally propose mitigation strategies for the operation of next-generation qubits in a radio-pure environment.

Non-linearity in the system of quasiparticles of a superconducting resonator

  1. M. Vignati,
  2. C. Bellenghi,
  3. L. Cardani,
  4. N. Casali,
  5. I. Colantoni,
  6. and A. Cruciani
We observed a strong non-linearity in the system of quasiparticles of a superconducting aluminum resonator, due to the Cooper-pair breaking from the absorbed readout power. We observed
both negative and positive feedback effects, controlled by the detuning of the readout frequency, which are able to alter the relaxation time of quasiparticles by a factor greater than 10. We estimate that the (70+/-5) % of the total non-linearity of the device is due to quasiparticles.