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.

Demonstration of tunable three-body interactions between superconducting qubits

  1. Tim Menke,
  2. William P. Banner,
  3. Thomas R. Bergamaschi,
  4. Agustin Di Paolo,
  5. Antti Vepsäläinen,
  6. Steven J. Weber,
  7. Roni Winik,
  8. Alexander Melville,
  9. Bethany M. Niedzielski,
  10. Danna Rosenberg,
  11. Kyle Serniak,
  12. Mollie E. Schwartz,
  13. Jonilyn L. Yoder,
  14. Alán Aspuru-Guzik,
  15. Simon Gustavsson,
  16. Jeffrey A. Grover,
  17. Cyrus F. Hirjibehedin,
  18. Andrew J. Kerman,
  19. and William D. Oliver
Nonpairwise multi-qubit interactions present a useful resource for quantum information processors. Their implementation would facilitate more efficient quantum simulations of molecules
and combinatorial optimization problems, and they could simplify error suppression and error correction schemes. Here we present a superconducting circuit architecture in which a coupling module mediates 2-local and 3-local interactions between three flux qubits by design. The system Hamiltonian is estimated via multi-qubit pulse sequences that implement Ramsey-type interferometry between all neighboring excitation manifolds in the system. The 3-local interaction is coherently tunable over several MHz via the coupler flux biases and can be turned off, which is important for applications in quantum annealing, analog quantum simulation, and gate-model quantum computation.

Distinguishing multi-spin interactions from lower-order effects

  1. Thomas R. Bergamaschi,
  2. Tim Menke,
  3. William P. Banner,
  4. Agustin Di Paolo,
  5. Steven J. Weber,
  6. Cyrus F. Hirjibehedin,
  7. Andrew J. Kerman,
  8. and William D. Oliver
Multi-spin interactions can be engineered with artificial quantum spins. However, it is challenging to verify such interactions experimentally. Here we describe two methods to characterize
the n-local coupling of n spins. First, we analyze the variation of the transition energy of the static system as a function of local spin fields. Standard measurement techniques are employed to distinguish n-local interactions between up to five spins from lower-order contributions in the presence of noise and spurious fields and couplings. Second, we show a detection technique that relies on time dependent driving of the coupling term. Generalizations to larger system sizes are analyzed for both static and dynamic detection methods, and we find that the dynamic method is asymptotically optimal when increasing the system size. The proposed methods enable robust exploration of multi-spin interactions across a broad range of both coupling strengths and qubit modalities.

Characterizing and optimizing qubit coherence based on SQUID geometry

  1. Jochen Braumüller,
  2. Leon Ding,
  3. Antti Vepsäläinen,
  4. Youngkyu Sung,
  5. Morten Kjaergaard,
  6. Tim Menke,
  7. Roni Winik,
  8. David Kim,
  9. Bethany M. Niedzielski,
  10. Alexander Melville,
  11. Jonilyn L. Yoder,
  12. Cyrus F. Hirjibehedin,
  13. Terry P. Orlando,
  14. Simon Gustavsson,
  15. and William D. Oliver
The dominant source of decoherence in contemporary frequency-tunable superconducting qubits is 1/f flux noise. To understand its origin and find ways to minimize its impact, we systematically
study flux noise amplitudes in more than 50 flux qubits with varied SQUID geometry parameters and compare our results to a microscopic model of magnetic spin defects located at the interfaces surrounding the SQUID loops. Our data are in agreement with an extension of the previously proposed model, based on numerical simulations of the current distribution in the investigated SQUIDs. Our results and detailed model provide a guide for minimizing the flux noise susceptibility in future circuits.