Qubit-compatible substrates with superconducting through-silicon vias

  1. K. Grigoras,
  2. N. Yurttagül,
  3. J.-P. Kaikkonen,
  4. E. T. Mannila,
  5. P. Eskelinen,
  6. D. P. Lozano,
  7. H.-X. Li,
  8. M. Rommel,
  9. D. Shiri,
  10. N. Tiencken,
  11. S. Simbierowicz,
  12. A. Ronzani,
  13. J. Hätinen,
  14. D. Datta,
  15. V. Vesterinen,
  16. L. Grönberg,
  17. J. Biznárová,
  18. A. Fadavi Roudsari,
  19. S. Kosen,
  20. A. Osman,
  21. J. Hassel,
  22. J. Bylander,
  23. and J. Govenius
We fabricate and characterize superconducting through-silicon vias and electrodes suitable for superconducting quantum processors. We measure internal quality factors of a million for
test resonators excited at single-photon levels, when vias are used to stitch ground planes on the front and back sides of the wafer. This resonator performance is on par with the state of the art for silicon-based planar solutions, despite the presence of vias. Via stitching of ground planes is an important enabling technology for increasing the physical size of quantum processor chips, and is a first step toward more complex quantum devices with three-dimensional integration.

Rotating-frame relaxation as a noise spectrum analyzer of a superconducting qubit undergoing driven evolution

  1. F. Yan,
  2. S. Gustavsson,
  3. J. Bylander,
  4. X. Jin,
  5. F. Yoshihara,
  6. D. G. Cory,
  7. Y. Nakamura,
  8. T. P. Orlando,
  9. and W. D. Oliver
Gate operations in a quantum information processor are generally realized by tailoring specific periods of free and driven evolution of a quantum system. Unwanted environmental noise,
which may in principle be distinct during these two periods, acts to decohere the system and increase the gate error rate. While there has been significant progress characterizing noise processes during free evolution, the corresponding driven-evolution case is more challenging as the noise being probed is also extant during the characterization protocol. Here we demonstrate the noise spectroscopy (0.1 – 200 MHz) of a superconducting flux qubit during driven evolution by using a robust spin-locking pulse sequence to measure relaxation (T1rho) in the rotating frame. In the case of flux noise, we resolve spectral features due to coherent fluctuators, and further identify a signature of the 1MHz defect in a time-domain spin-echo experiment. The driven-evolution noise spectroscopy complements free-evolution methods, enabling the means to characterize and distinguish various noise processes relevant for universal quantum control.