Jeffrey M. Knecht

Bosonic Error Correction with Fluxonium

  1. Shantanu R. Jha,
  2. Shoumik D. Chowdhury,
  3. Gabriele Rolleri,
  4. Anaida Ali,
  5. Lev-Arcady Sellem,
  6. Réouven Assouly,
  7. David Pahl,
  8. Lukas Pahl,
  9. Junyoung An,
  10. Farid Hassani,
  11. Hung-Yu Tsao,
  12. Chia-Chin Tsai,
  13. Aranya Goswami,
  14. Jeremie Boudreault,
  15. Jeffrey M. Gertler,
  16. Michael A. Gingras,
  17. Bethany M. Niedzielski,
  18. Jeffrey M. Knecht,
  19. Mollie E. Schwartz,
  20. Kyle Serniak,
  21. Jeffrey A. Grover,
  22. Baptiste Royer,
  23. Max Hays,
  24. and William D. Oliver
Bosonic quantum error correction (QEC) offers a hardware-efficient route to fault-tolerant quantum computing. To date, however, superconducting circuit implementations of bosonic codes
have utilized centimeter-scale 3D microwave cavities controlled by fixed-frequency transmon qubits, with logical lifetimes limited by transmon bit-flip errors. Here, we realize bosonic QEC in a fully planar architecture by pairing a heavy fluxonium, whose 451±70 μs bit-flip lifetime exceeds that of any control qubit in previous demonstrations, with an on-chip Archimedean spiral resonator several orders of magnitude smaller in mode volume than prior 3D cavities. We prepare finite-energy Gottesman-Kitaev-Preskill (GKP) states and stabilize them using measurement-free error correction with rapid fluxonium reset, extending the logical lifetime by a factor of 1.59±0.05. These results provide the first demonstration of resonator control using a weakly coupled fluxonium and, with it, the first realization of standalone bosonic QEC in a fully planar superconducting circuit architecture.
arxiv pdf

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