Shulou(Shulou.com)11/24 Report--

Thanks to CTOnews.com netizen LexPan for the clue delivery! CTOnews.com, July 13, Chinese researchers have successfully completed the preparation and verification of 51 superconducting qubit clusters, breaking the world record for the number of true entangled bits in all quantum systems, and demonstrating the variational quantum algorithm based on measurement for the first time.

The development history of the number of bits in ▲ quantum true entangled states. (photo Source: official team) the study was conducted by Academician Pan Jianwei of the University of Science and Technology of China, Zhu Xiaobo and Peng Chengzhi team, and Yuan Jie of Peking University. The results were published in the journal Nature on July 12 (CTOnews.com attached DOI:10.1038 / s41586,023-06195-1).

Large-scale preparation of true entangled states requires highly connected quantum systems, high-fidelity multi-bit quantum gates and efficient and accurate fidelity characterization of quantum states. because it is difficult to achieve these requirements for quantum system performance, manipulation and verification, the scale of true entanglement bits failed to exceed 24 qubits.

In fact, some people have tried to use a large number of qubits to achieve this goal before, but none of them can verify the existence of entanglement.

For two entangled particles, changing the properties of one particle will change the same properties of the other particle at the same time. For more particles, not only can each pair of particles be entangled, but all particles can be entangled with each other.

Researchers studied how to entangle three or four photons in this more complex way in the late 1980s, and previously implemented a 27-qubit quantum computer.

On the basis of the "Zuchongzhi II" superconducting quantum computing prototype built earlier, Chinese researchers further improved the fidelity of parallel multi-bit quantum gates to 99.05% and the reading accuracy to 95.09%. Combined with the large-scale quantum state fidelity verification scheme proposed by the research team, the 51-bit cluster state preparation and verification were successfully realized.

Using a prototype of superconducting quantum computing in China, the researchers successfully entangled 51 qubits in a row and 30 qubits in a two-dimensional plane, setting records in each case.

▲ used Zuchongzhi II's 51-bit one-dimensional cluster state to prepare circuits and quantum state fidelity results. "this success stems from fine calibration of the equipment and thoughtful design choices," said Nathan Lacroix of the Federal Institute of Technology in Zurich. "this shows the power of Zuchongzhi computers." He pointed out that other researchers had previously created similar systems with up to 57 qubits, but could not verify whether each qubit was entangled with other qubits.

"entanglement is one of the key differences between traditional computers and quantum computers, and it is also a key element of quantum algorithms. Therefore, displaying a large number of entangled qubits is an important benchmark for quantum computers," said Charles Hill of the University of New South Wales in Australia. Hill and his colleagues tried to do a similar feat using a 65-qubit device, but only proved that the qubits were entangled in pairs, not as a whole.

"We must develop a new method of observing entanglement," Zhu Xiaobo said. This involves how to skillfully select a minimum set of measurements to collect enough information to describe what qubits are doing without spending too much time or computing resources.

Christian Andersen of Delft University of Technology in the Netherlands says that although it is not clear how 51 entangled qubits are used in computation, the researchers have made impressive technical achievements and created a very complex system because it has no counterpart in classical physics. "this work can inspire other researchers to understand what we can actually do with superconducting qubits," he said. "

"this work greatly refreshes the record of the number of true entanglement bits in the quantum system from 24 to 51, which fully demonstrates the excellent scalability of the superconducting quantum computing system." Pan Jianwei said that on this basis, the research team implemented the measurement-based variational quantum algorithm for the first time, which laid the foundation for the practical application of the measurement-based quantum computing scheme.

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