Shasha Zhu

Millikelvin digital-to-analog converter for superconducting quantum processors

  1. Ruizi Hu,
  2. Zongyuan Li,
  3. Zhancheng Yao,
  4. Yufei Wu,
  5. Qiang Zhang,
  6. Yining Jiao,
  7. Quan Guan,
  8. Lijing Jin,
  9. Wangwei Lan,
  10. Chengyao Li,
  11. Lu Ma,
  12. Liyong Mao,
  13. Huijuan Zhan,
  14. Ze Zhan,
  15. Ran Gao,
  16. Lijuan Hu,
  17. Kannan Lu,
  18. Xizheng Ma,
  19. Tenghui Wang,
  20. Peng Xiang,
  21. Chunqing Deng,
  22. and Shasha Zhu
Scaling superconducting quantum processors is increasingly constrained by the wiring, heat load, and calibration overhead associated with delivering high-resolution analog signals from
room temperature to qubits at millikelvin temperature. Here we demonstrate a superconducting digital-to-analog converter (DAC) integrated with high-coherence fluxonium qubits in a multi-chip module architecture. The DACs generate persistent analog flux signals for tuning qubit parameters and are programmed deterministically using single-flux-quantum (SFQ) pulses, providing a digital interface compatible with established SFQ routing and demultiplexing technologies. Operating at millikelvin temperature, the DACs enable in-situ tuning of fluxonium qubits without measurable degradation of qubit coherence. The presented device provides a static control primitive for flux-tunable qubits, enabling parameter homogenization and eliminating the need for individual room-temperature DC bias lines. These results establish SFQ-programmable millikelvin DACs as a building block for digitally controlled superconducting quantum processors.
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