Huijuan Zhan

Identity and Quantify Various Dissipation Mechanisms of Josephson Junction in Superconducting Circuits

  1. Hao Deng,
  2. Huijuan Zhan,
  3. Lijuan Hu,
  4. Hui-Hai Zhao,
  5. Ran Gao,
  6. Kannan Lu,
  7. Xizheng Ma,
  8. Zhijun Song,
  9. Fei Wang,
  10. Tenghui Wang,
  11. Feng Wu,
  12. Tian Xia,
  13. Gengyan Zhang,
  14. Xiaohang Zhang,
  15. and Chunqing Deng
Pinpointing the dissipation mechanisms and evaluating their impacts to the performance of Josephson junction (JJ) are crucial for its application in superconducting circuits. In this
work, we demonstrate the junction-embedded resonator (JER) as a platform which enables us to identify and quantify various dissipation mechanisms of JJ. JER is constructed by embedding JJ in the middle of an open-circuit, 1/2 {\lambda} transmission-line resonator. When the 1st and 2nd harmonics of JER are excited, JJ experiences different boundary conditions, and is dominated by internal and external dissipations, respectively. We systematically study these 2 dissipation mechanisms of JJ by varying the JJ area and number. Our results unveil the completely different behaviors of these 2 dissipation mechanisms, and quantitatively characterize their contributions, shedding a light on the direction of JJ optimization in various applications.
arxiv pdf

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