Abstract
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 of up to 8.1 × 105, which is comparable with the performance of our transmon qubits fabricated on a single-crystal sapphire substrate. We use these interconnects to link five quantum modules with intermodule quantum state transfer and Bell state fidelities of up to 99%. To benchmark the overall performance of the processor, we create maximally entangled, multiqubit Greenberger–Horne–Zeilinger states. The generated intermodule four-qubit Greenberger–Horne–Zeilinger state exhibits 92.0% fidelity. We also entangle up to 12 qubits in a Greenberger–Horne–Zeilinger state with 55.8 ± 1.8% fidelity, which is above the genuine multipartite entanglement threshold of 1/2.
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Data availability
The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.
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Acknowledgements
We thank Y. He and J. Liu for helpful discussions and critical reading of the manuscript. This work was supported by the Key Area Research and Development Program of Guangdong Province (2018B030326001); the National Natural Science Foundation of China (U1801661, 12174178); the Guangdong Innovative and Entrepreneurial Research Team Program (2016ZT06D348); the Guangdong Provincial Key Laboratory (2019B121203002); the Science, Technology and Innovation Commission of Shenzhen Municipality (KYTDPT20181011104202253, KQTD20210811090049034); the Shenzhen-Hong Kong Cooperation Zone for Technology and Innovation (HZQB-KCZYB-2020050); and the NSF of Beijing (Z190012) and the Innovation Program for Quantum Science and Technology (2021ZD0301703).
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Y. Zhong conceived the idea and supervised the experiment. S.L. supervised the device fabrication and supported the infrastructure setup. J.N. and Y. Zhong wire-bonded the cables, performed the measurement and analysed the data. L.Z. fabricated the devices and designed the sample holder. Y.L. and J.Q. assisted in the measurement. Y. Zhong built the custom microwave electronics. Y. Zhong and A.N.C. wrote the manuscript. All the authors contributed to the discussions and production of the manuscript.
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Y. Zhong, S.L., D.Y., J.N. and L.Z. are inventors on a provisional patent application (China, 202210723073.8) that has been filed relating to this work. The other authors declare no competing interests.
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Supplementary Figs. 1–8, Sections I–V and Tables 1–3.
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Niu, J., Zhang, L., Liu, Y. et al. Low-loss interconnects for modular superconducting quantum processors. Nat Electron 6, 235–241 (2023). https://doi.org/10.1038/s41928-023-00925-z
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DOI: https://doi.org/10.1038/s41928-023-00925-z
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