Observation of classical-quantum crossover of 1/f flux noise and its paramagnetic temperature dependence

  1. C. M. Quintana,
  2. Yu Chen,
  3. D. Sank,
  4. A. G. Petukhov,
  5. T. C. White,
  6. Dvir Kafri,
  7. B. Chiaro,
  8. A. Megrant,
  9. R. Barends,
  10. B. Campbell,
  11. Z. Chen,
  12. A. Dunsworth,
  13. A. G. Fowler,
  14. R. Graff,
  15. E. Jeffrey,
  16. J. Kelly,
  17. E. Lucero,
  18. J. Y. Mutus,
  19. M. Neeley,
  20. C. Neill,
  21. P. J. J. O'Malley,
  22. P. Roushan,
  23. A. Shabani,
  24. A. Vainsencher,
  25. J. Wenner,
  26. H. Neven,
  27. and John M. Martinis
By analyzing the dissipative dynamics of a tunable gap flux qubit, we extract both sides of its two-sided environmental flux noise spectral density over a range of frequencies around 2kBT/h≈1GHz, allowing for the observation of a classical-quantum crossover. Below the crossover point, the symmetric noise component follows a 1/f power law that matches the magnitude of the 1/f noise near 1Hz. The antisymmetric component displays a 1/T dependence below 100mK, providing dynamical evidence for a paramagnetic environment. Extrapolating the two-sided spectrum predicts the linewidth and reorganization energy of incoherent resonant tunneling between flux qubit wells.
arxiv pdf

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