Gregory Calusine

Improving Transmon Qubit Performance with Fluorine-based Surface Treatments

  1. Michael A. Gingras,
  2. Bethany M. Niedzielski,
  3. Kevin A. Grossklaus,
  4. Duncan Miller,
  5. Felipe Contipelli,
  6. Kate Azar,
  7. Luke D Burkhart,
  8. Gregory Calusine,
  9. Daniel Davis,
  10. Renée DePencier Piñero,
  11. Jeffrey M. Gertler,
  12. Thomas M. Hazard,
  13. Cyrus F. Hirjibehedin,
  14. David K. Kim,
  15. Jeffrey M. Knecht,
  16. Alexander J. Melville,
  17. Christopher O'Connell,
  18. Robert A. Rood,
  19. Ali Sabbah,
  20. Hannah Stickler,
  21. Jonilyn L. Yoder,
  22. William D. Oliver,
  23. Mollie E. Schwartz,
  24. and Kyle Serniak
Reducing materials and processing-induced decoherence is critical to the development of utility-scale quantum processors based on superconducting qubits. Here we report on the impact
of two fluorine-based wet etches, which we use to treat the silicon surface underneath the Josephson junctions (JJs) of fixed-frequency transmon qubits made with aluminum base metallization. Using several materials analysis techniques, we demonstrate that these surface treatments can remove germanium residue introduced by our JJ fabrication with no other changes to the overall process flow. These surface treatments result in significantly improved energy relaxation times for the highest performing process, with median T1=334 μs, corresponding to quality factor Q=6.6×106. This result suggests that the metal-substrate interface directly underneath the JJs was a major contributor to microwave loss in these transmon qubit circuits prior to integration of these surface treatments. Furthermore, this work illustrates how materials analysis can be used in conjunction with quantum device performance metrics to improve performance in superconducting qubits.
arxiv pdf

Fabrication of superconducting through-silicon vias

  1. Justin L. Mallek,
  2. Donna-Ruth W. Yost,
  3. Danna Rosenberg,
  4. Jonilyn L. Yoder,
  5. Gregory Calusine,
  6. Matt Cook,
  7. Rabindra Das,
  8. Alexandra Day,
  9. Evan Golden,
  10. David K. Kim,
  11. Jeffery Knecht,
  12. Bethany M. Niedzielski,
  13. Mollie Schwartz,
  14. Arjan Sevi,
  15. Corey Stull,
  16. Wayne Woods,
  17. Andrew J. Kerman,
  18. and William D. Oliver
Increasing circuit complexity within quantum systems based on superconducting qubits necessitates high connectivity while retaining qubit coherence. Classical micro-electronic systems
have addressed interconnect density challenges by using 3D integration with interposers containing through-silicon vias (TSVs), but extending these integration techniques to superconducting quantum systems is challenging. Here, we discuss our approach for realizing high-aspect-ratio superconducting TSVs\textemdash 10 μm wide by 20 μm long by 200 μm deep\textemdash with densities of 100 electrically isolated TSVs per square millimeter. We characterize the DC and microwave performance of superconducting TSVs at cryogenic temperatures and demonstrate superconducting critical currents greater than 20 mA. These high-aspect-ratio, high critical current superconducting TSVs will enable high-density vertical signal routing within superconducting quantum processors.
arxiv pdf