Lu Ma

Converting qubit relaxation into erasures with a single fluxonium

  1. Chenlu Liu,
  2. Yulong Li,
  3. Jiahui Wang,
  4. Quan Guan,
  5. Lijing Jin,
  6. Lu Ma,
  7. Ruizi Hu,
  8. Tenghui Wang,
  9. Xing Zhu,
  10. Hai-Feng Yu,
  11. Chunqing Deng,
  12. and Xizheng Ma
Qubits that experience predominantly erasure errors offer distinct advantages for fault-tolerant operation. Indeed, dual-rail encoded erasure qubits in superconducting cavities and
transmons have demonstrated high-fidelity operations by converting physical-qubit relaxation into logical-qubit erasures, but this comes at the cost of increased hardware overhead and circuit complexity. Here, we address these limitations by realizing erasure conversion in a single fluxonium operated at zero flux, where the logical state is encoded in its 0-2 subspace. A single, carefully engineered resonator provides both mid-circuit erasure detection and end-of-line (EOL) logical measurement. Post-selection on non-erasure outcomes results in more than four-fold increase of the logical lifetime, from 193 μs to 869 μs. Finally, we characterize measurement-induced logical dephasing as a function of measurement power and frequency, and infer that each erasure check contributes a negligible error of 7.2×10−5. These results establish integer-fluxonium as a promising, resource-efficient platform for erasure-based error mitigation, without requiring additional hardware.
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