4.8 Article

Low-loss interconnects for modular superconducting quantum processors

Journal

NATURE ELECTRONICS
Volume 6, Issue 3, Pages 235-241

Publisher

NATURE PORTFOLIO
DOI: 10.1038/s41928-023-00925-z

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Low-loss superconducting aluminium cables and on-chip impedance transformers are used to connect qubit modules and create high-fidelity intermodule state transfer in superconducting quantum computing networks. Scaling is a key challenge in superconducting quantum computing, which can be addressed by building modular systems with suitable interconnects. The reported low-loss interconnects based on pure aluminium coaxial cables and on-chip impedance transformers demonstrate comparable performance with transmon qubits and enable intermodule quantum state transfer with high fidelity.
Low-loss superconducting aluminium cables and on-chip impedance transformers can be used to link qubit modules and create superconducting quantum computing networks with high-fidelity intermodule state transfer. 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 x 10(5), 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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