Fei Wang

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

Unraveling the role of disorderness in superconducting materials on qubit coherence

  1. Ran Gao,
  2. Feng Wu,
  3. Hantao Sun,
  4. Jianjun Chen,
  5. Hao Deng,
  6. Xizheng Ma,
  7. Xiaohe Miao,
  8. Zhijun Song,
  9. Xin Wan,
  10. Fei Wang,
  11. Tian Xia,
  12. Make Ying,
  13. Chao Zhang,
  14. Yaoyun Shi,
  15. Hui-Hai Zhao,
  16. and Chunqing Deng
Introducing disorderness in the superconducting materials has been considered promising to enhance the electromagnetic impedance and realize noise-resilient superconducting qubits.
Despite a number of pioneering implementations, the understanding of the correlation between the material disorderness and the qubit coherence is still developing. Here, we demonstrate the first and a systematic characterization of fluxonium qubits with the superinductors made from titanium-aluminum-nitride with varied disorderness. From qubit noise spectroscopy, the flux noise and the dielectric loss are extracted as a measure of the coherence properties. Our results reveal that the 1/f flux noise dominates the qubit decoherence around the flux-frustration point, strongly correlated with the material disorderness; while the dielectric loss remains low under a wide range of material properties. From the flux-noise amplitudes, the areal density (σ) of the phenomenological spin defects and material disorderness are found to be approximately correlated by σ∝ρ3xx, or effectively (kFl)−3. This work has provided new insights on the origin of decoherence channels within superconductors, and could serve as a useful guideline for material design and optimization.
arxiv pdf