Researchers at the University of Science and Technology of China (USTC) have unveiled a new prototype of a programmable photonic quantum computer, known as Jiuzhang 4.0. According to USTC, Jiuzhang 4.0 has demonstrated the most credible instance of quantum supremacy to date, having achieved a computational speed up of 10⁵⁴ times compared to the world’s faster supercomputer, El Capitan, when applied to solving Gaussian boson sampling tasks. The results, published in Nature, show that the system completed these Gaussian boson sampling calculations in approximately 25.6 microseconds.
The research was conducted by a team led by Pan Jianwei, Lu Chaoyang, Zhang Qiang, and Liu Naile from the University of Science and Technology of China, in collaboration with the Jinan Institute of Quantum Technology, Shanxi University, Tsinghua University, Shanghai Artificial Intelligence Laboratory, Laoshan Laboratory, and the National Research Center for Parallel Computer Engineering and Technology. Supporting this research was China’s National Major Science and Technology Project, the National Natural Science Foundation of China, the Ministry of Science and Technology, the Chinese Academy of Sciences, Anhui Province, Shandong Province, Shanghai Municipality, Shanxi Province, and the New Cornerstone Foundation.
According to the paper, the processors “incorporates 1,024 high-efficiency squeezed states into a hybrid spatial–temporal encoded 8,176-mode circuit. By achieving 92% source efficiency and 51% overall system efficiency, the processor produces samples with detection events up to 3,050 photons, representing an order-of-magnitude increase in scale over previous demonstrations.”
One of the challenges in achieving this, according to USTC’s announcement, was in overcoming photon loss – a problem that emerges as coding circuits increase in size and complexity, posing a serious obstacle to scalability. To address this, the research team developed an optical parametric oscillator (OPO) source and a spatiotemporal hybrid coding interferometer, which resulted in an improvement of more than 10 times over the previous best results.
The significance of Gaussian boson sampling, said the paper, is that it is effective in demonstrating quantum advantage, and also its ability to generate bosonic error-correcting codes for fault-tolerance quantum computing. In 2022, Canadian photonic quantum company Xanadu performed a similar demonstration, producing 216 squeezed-state qubits, demonstrating a similar quantum advantage.
Jiuzhang 4.0 is the latest generation in China’s Jiuzhang photonic quantum computing series, with the first Jiuzhang having been unveiled in 2020, with 76 photons. In 2020, the 113-photon Jiuzhang-2 introduced, followed by the 255-photon Jiuzhang-3 in 2023.
Read the paper here.
