Breakthrough in quantum computing: 5 superconducting quantum chips are interconnected

Recently, the superconducting quantum computing team of Shenzhen Institute of Quantum Science and Engineering of Southern University of Science and Technology (hereinafter referred to as SUSTech) has made breakthroughs in distributed quantum computing research. They proposed and realized ultra-low-loss quantum chip interconnection technology, which improved the fidelity of quantum state transmission between chips to the single-chip level (99%), and the research team realized the interconnection of 5 quantum chips and demonstrated the 12-bit maximum entangled state across 3 chips, laying a solid foundation for large-scale and scalable distributed quantum computing networks.

On February 16, the relevant research results were published in the international academic journal “Nature-Electronics” under the title “Low-loss interconnects for modular superconducting quantum processors”.Nature Electronics) on.

Schematic diagram of the “interconnection of 5 quantum chips” Image source: Nature Electronics

In recent years, superconducting quantum computing has developed rapidly, and the number of operable qubits is expected to expand to more than thousands in the next few years, and on this basis, the practical application of noisy medium-scale quantum devices (NISQ) will be explored. However, superconducting qubits are large in size and each bit requires dedicated RF control circuits, so as the number of bits increases, it becomes increasingly difficult to integrate more bits on a single chip. The distributed quantum computing scheme is expected to break through the dilemma of single-chip integration by interconnecting multiple quantum chips to build a large-scale quantum processor, but the current high-performance interconnection between chips is a technical bottleneck.

In this study, after nearly 2 years of technical research, the research team has realized a series of technological innovations: developed ultra-low loss and easy to bond superconducting coaxial wires, and integrated impedance converters on quantum chips to reduce the loss of quantum chip connection interfaces. Through these technological innovations, the team achieved the interconnection of ultra-high-performance superconducting quantum chips, and the channel single-photon quality factor reached 8.1×105, an order of magnitude higher than the previously reported results, and the channel coherence time (~26.4us) reached the level of qubits on a single chip. On this basis, the team achieves a fidelity of 99% of cross-chip quantum state transmission, which is internationally leading and lays the foundation for the large-scale expansion of superconducting quantum processors.

Using this low-loss chip interconnection technology, the research team realized the interconnection of 5 quantum chips, each of which integrates 4 qubits to form a 20-bit distributed quantum processor. Based on the distributed quantum processor, the research team demonstrated the preparation of cross-chip multi-bit entangled states, and realized the cross-chip distributed 4-bit Greenberger-Horne-Zeilinger (GHZ) entangled state, and its fidelity reached 92%, reaching the level of preparing homogeneous multi-bit entangled states on a single chip, which is the first time that a distributed superconducting quantum processor has achieved single-chip performance in the preparation of quantum entangled states, which is a milestone.

Distributed superconducting quantum processors Image source: Nature Electronics

Finally, through more cross-chip quantum state transmission and logic gate manipulation on a single chip, the research team achieved a maximum entangled state of 12 bits across three chips, and this GHZ state fidelity reached 55.8%.

In the research results, Niu Jingjing, assistant researcher of the Institute of Mass Biological Science and Engineering of Southern Science and Technology, is the first author of the paper, and associate researchers Liu Song and Zhong Youpeng are the corresponding authors. SUSTech is the first unit of papers. The research work has been strongly supported by the Department of Science and Technology of Guangdong Province, the Shenzhen Municipal Science and Technology Innovation Commission, the National Natural Science Foundation of China, and Southern University of Science and Technology. (Source: China Science News Zhao Guangli)

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