Low-loss interconnects for modular superconducting quantum processors

  1. Jingjing Niu,
  2. Libo Zhang,
  3. Yang Liu,
  4. Jiawei Qiu,
  5. Wenhui Huang,
  6. Jiaxiang Huang,
  7. Hao Jia,
  8. Jiawei Liu,
  9. Ziyu Tao,
  10. Weiwei Wei,
  11. Yuxuan Zhou,
  12. Wanjing Zou,
  13. Yuanzhen Chen,
  14. Xiaowei Deng,
  15. Xiuhao Deng,
  16. Changkang Hu,
  17. Ling Hu,
  18. Jian Li,
  19. Dian Tan,
  20. Yuan Xu,
  21. Fei Yan,
  22. Tongxing Yan,
  23. Song Liu,
  24. Youpeng Zhong,
  25. Andrew N. Cleland,
  26. and Dapeng Yu
Scaling is now a key challenge in superconducting quantum computing. One solution is to build modular systems in which smaller-scale quantum modules are individually constructed and calibrated, and then assembled into a larger architecture. This, however, requires the development of suitable interconnects. Here, we report low-loss interconnects based on pure aluminium coaxial cables and on-chip impedance transformers featuring quality factors up to 8.1×105, which is comparable to the performance of our transmon qubits fabricated on single-crystal sapphire substrate. We use these interconnects to link five quantum modules with inter-module quantum state transfer and Bell state fidelities up to 99\%. To benchmark the overall performance of the processor, we create maximally-entangled, multi-qubit Greenberger-Horne-Zeilinger (GHZ) states. The generated inter-module four-qubit GHZ state exhibits 92.0\% fidelity. We also entangle up to 12 qubits in a GHZ state with 55.8±1.8% fidelity, which is above the genuine multipartite entanglement threshold of 1/2. These results represent a viable modular approach for large-scale superconducting quantum processors.
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