Chinese scientists have realized the preparation of 51 superconducting qubit clusters

A research team composed of Pan Jianwei, Zhu Xiaobo and Peng Chengzhi, Institute of Quantum Information and Quantum Science and Technology Innovation, Chinese Academy of Sciences, University of Science and Technology of China, cooperated with Yuan Xiao of Peking University to successfully realize the preparation and verification of 51 superconducting qubit clusters, set a world record for the number of true entangled bits in all quantum systems, and demonstrated a measurement-based variational quantum algorithm for the first time. On July 12, the research results were published online in the journal Nature.


Wire and quantum state fidelity results prepared by using the 51-bit one-dimensional cluster state completed by Zu Chongzhi II. Photo courtesy of China University of Science and Technology

Pan Jianwei introduced that the work has greatly broken the record of the number of true entangled bits in each quantum system from the original 24 to 51, fully demonstrating the excellent scalability of the superconducting quantum computing system, which is of great significance for the study of many-body quantum entanglement, the realization of large-scale quantum algorithms and measurement-based quantum computing.

Quantum entanglement is one of the most mysterious and fundamental properties of quantum mechanics, as well as the core resource of quantum information processing and one of the fundamental sources of the acceleration effect of quantum computing. For many years, achieving large-scale multi-qubit entanglement has been the goal of scientists around the world. Since the preparation of 3-bit entangled states was first realized by nuclear magnetic resonance system in 1998, the preparation of true many-body entangled states has become an important characterization method for the large-scale expansion of various physical systems, including photons, ion traps, diamond nitrogen vacancy color centers, neutral atoms and superconducting qubits.

Among them, superconducting qubits have the advantage of large-scale expansion and have developed rapidly in recent years. Chinese scientists have made a series of important achievements in the preparation of superconducting qubit many-body entanglement, and have successively completed the preparation of true entanglement states of 10 bits, 12 bits and 18 bits since 2017, constantly refreshing the record of the number of entangled bits in the field of superconducting quantum computing.

However, larger-scale preparation of true entangled states requires quantum systems with high connectivity, high-fidelity multi-bit quantum gates, and efficient and accurate quantum state fidelity characterization methods. Due to the difficulty of achieving these requirements for the performance, manipulation and verification methods of quantum systems, the scale of true entangled bits has not exceeded 24 qubits.

In this study, on the basis of the “Zu Chongzhi II” superconducting quantum computing prototype built in the early stage, the research team further improved the fidelity of parallel multi-bit quantum gates to 99.05% and the reading accuracy to 95.09%, and successfully realized the preparation and verification of 51-bit cluster states in combination with the large-scale quantum state fidelity verification and determination scheme proposed by the research team. Finally, the fidelity of the 51-bit one-dimensional cluster reached 0.637±0.030, exceeding the 0.5 entanglement determination threshold by 13 standard deviations.

On this basis, the research team carried out the solution of the eigenenergy of small-scale perturbation plane code by combining the measurement-based variational quantum solver, and realized the measurement-based variational quantum algorithm for the first time, laying a foundation for the practical application of measurement-based quantum computing schemes. (Source: Wang Min, China Science News)

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