Long-distance transmon coupler with CZ gate fidelity above 99.8%

  1. Fabian Marxer,
  2. Antti Vepsäläinen,
  3. Shan W. Jolin,
  4. Jani Tuorila,
  5. Alessandro Landra,
  6. Caspar Ockeloen-Korppi,
  7. Wei Liu,
  8. Olli Ahonen,
  9. Adrian Auer,
  10. Lucien Belzane,
  11. Ville Bergholm,
  12. Chun Fai Chan,
  13. Kok Wai Chan,
  14. Tuukka Hiltunen,
  15. Juho Hotari,
  16. Eric Hyyppä,
  17. Joni Ikonen,
  18. David Janzso,
  19. Miikka Koistinen,
  20. Janne Kotilahti,
  21. Tianyi Li,
  22. Jyrgen Luus,
  23. Miha Papic,
  24. Matti Partanen,
  25. Jukka Räbinä,
  26. Jari Rosti,
  27. Mykhailo Savytskyi,
  28. Marko Seppälä,
  29. Vasilii Sevriuk,
  30. Eelis Takala,
  31. Brian Tarasinski,
  32. Manish J. Thapa,
  33. Francesca Tosto,
  34. Natalia Vorobeva,
  35. Liuqi Yu,
  36. Kuan Yen Tan,
  37. Juha Hassel,
  38. Mikko Möttönen,
  39. and Johannes Heinsoo
Tunable coupling of superconducting qubits has been widely studied due to its importance for isolated gate operations in scalable quantum processor architectures. Here, we demonstrate a tunable qubit-qubit coupler based on a floating transmon device which allows us to place qubits at least 2 mm apart from each other while maintaining over 50 MHz coupling between the coupler and the qubits. In the introduced tunable-coupler design, both the qubit-qubit and the qubit-coupler couplings are mediated by two waveguides instead of relying on direct capacitive couplings between the components, reducing the impact of the qubit-qubit distance on the couplings. This leaves space for each qubit to have an individual readout resonator and a Purcell filter needed for fast high-fidelity readout. In addition, the large qubit-qubit distance reduces unwanted non-nearest neighbor coupling and allows multiple control lines to cross over the structure with minimal crosstalk. Using the proposed flexible and scalable architecture, we demonstrate a controlled-Z gate with (99.81±0.02)% fidelity.
arxiv pdf

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