Jeffrey M. Gertler

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

Emergent Harmonics in Josephson Tunnel Junctions Due to Series Inductance

  1. Junghyun Kim,
  2. Max Hays,
  3. Ilan T. Rosen,
  4. Junyoung An,
  5. Helin Zhang,
  6. Aranya Goswami,
  7. Kate Azar,
  8. Jeffrey M. Gertler,
  9. Bethany M. Niedzielski,
  10. Mollie E. Schwartz,
  11. Terry P. Orlando,
  12. Jeffrey A. Grover,
  13. Kyle Serniak,
  14. and William D. Oliver
Josephson tunnel junctions are essential elements of superconducting quantum circuits. The operability of these circuits presumes a 2π-periodic sinusoidal potential of a tunnel junction,
but higher-order corrections to this Josephson potential, often referred to as „harmonics,“ cause deviations from the expected circuit behavior. Two potential sources for these harmonics are the intrinsic current-phase relationship of the Josephson junction and the inductance of the metallic traces connecting the junction to other circuit elements. Here, we introduce a method to distinguish the origin of the observed harmonics using nearly-symmetric superconducting quantum interference devices (SQUIDs). Spectroscopic measurements of level transitions in multiple devices reveal features that cannot be explained by a standard cosine potential, but are accurately reproduced when accounting for a second-harmonic contribution to the model. The observed scaling of the second harmonic with Josephson-junction size indicates that it is due almost entirely to the trace inductance. These results inform the design of next-generation superconducting circuits for quantum information processing and the investigation of the supercurrent diode effect.
arxiv pdf