Achieving millisecond coherence fluxonium through overlap Josephson junctions

  1. Fei Wang,
  2. Kannan Lu,
  3. Huijuan Zhan,
  4. Lu Ma,
  5. Feng Wu,
  6. Hantao Sun,
  7. Hao Deng,
  8. Yang Bai,
  9. Feng Bao,
  10. Xu Chang,
  11. Ran Gao,
  12. Xun Gao,
  13. Guicheng Gong,
  14. Lijuan Hu,
  15. Ruizi Hu,
  16. Honghong Ji,
  17. Xizheng Ma,
  18. Liyong Mao,
  19. Zhijun Song,
  20. Chengchun Tang,
  21. Hongcheng Wang,
  22. Tenghui Wang,
  23. Ziang Wang,
  24. Tian Xia,
  25. Hongxin Xu,
  26. Ze Zhan,
  27. Gengyan Zhang,
  28. Tao Zhou,
  29. Mengyu Zhu,
  30. Qingbin Zhu,
  31. Shasha Zhu,
  32. Xing Zhu,
  33. Yaoyun Shi,
  34. Hui-Hai Zhao,
  35. and Chunqing Deng
Fluxonium qubits are recognized for their high coherence times and high operation fidelities, attributed to their unique design incorporating over 100 Josephson junctions per superconducting loop. However, this complexity poses significant fabrication challenges, particularly in achieving high yield and junction uniformity with traditional methods. Here, we introduce an overlap process for Josephson junction fabrication that achieves nearly 100% yield and maintains uniformity across a 2-inch wafer with less than 5% variation for the phase slip junction and less than 2% for the junction array. Our compact junction array design facilitates fluxonium qubits with energy relaxation times exceeding 1 millisecond at the flux frustration point, demonstrating consistency with state-of-the-art dielectric loss tangents and flux noise across multiple devices. This work suggests the scalability of high coherence fluxonium processors using CMOS-compatible processes, marking a significant step towards practical quantum computing.
arxiv pdf

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