Renée DePencier Piñero

ZZ-Free Two-Transmon CZ Gate Mediated by a Fluxonium Coupler

  1. Junyoung An,
  2. Helin Zhang,
  3. Qi Ding,
  4. Leon Ding,
  5. Youngkyu Sung,
  6. Roni Winik,
  7. Junghyun Kim,
  8. Ilan T. Rosen,
  9. Kate Azar,
  10. Renee DePencier Piñero,
  11. Jeffrey M. Gertler,
  12. Michael Gingras,
  13. Bethany M. Niedzielski,
  14. Hannah Stickler,
  15. Mollie E. Schwartz,
  16. Joel I.J. Wang,
  17. Terry P. Orlando,
  18. Simon Gustavsson,
  19. Max Hays,
  20. Jeffrey A. Grover,
  21. Kyle Serniak,
  22. and William D. Oliver
Eliminating residual ZZ interactions in a two-qubit system is essential for reducing coherent errors during quantum operations. In a superconducting circuit platform, coupling two transmon
qubits via a transmon coupler has been shown to effectively suppress residual ZZ interactions. However, in such systems, perfect cancellation usually requires the qubit-qubit detuning to be smaller than the individual qubit anharmonicities, which exacerbates frequency crowding and microwave crosstalk. To address this limitation, we introduce TFT (Transmon-Fluxonium-Transmon) architecture, wherein two transmon qubits are coupled via a fluxonium qubit. The coupling mediated by the fluxonium eliminates residual ZZ interactions even for transmons detuned larger than their anharmonicities. We experimentally identified zero-ZZ interaction points at qubit-qubit detunings of 409 MHz and 616 MHz from two distinct TFT devices. We then implemented an adiabatic, coupler-flux-biased controlled-Z gate on both devices, achieving CZ gate fidelities of 99.64(6)% and 99.68(8)%.
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