For the first time, the University of Science and Technology of China verifies the quantum non-locality of star networks

The team of Academician Guo Guangcan of the University of Science and Technology of China has made important progress in the non-local research of quantum networks. Professor Li Chuanfeng, researcher Huang Yunfeng, associate researcher Zhang Chao and others collaborated with theoretical physicists from Spain, Switzerland and other countries to verify the non-locality of the whole network in the star quantum network for the first time. The results were published April 14 in Nature Communications.

Schematic diagram of star quantum network and experimental device diagram Courtesy of China University of Science and Technology

Bell nonlocality has always been a research hotspot in the field of quantum information. In recent years, non-locality in more complex quantum networks containing multiple independent sources has been explored. By including multiple independent hidden variables, new quantum associations can be generated in quantum networks that differ from traditional Bell nonlocalities. Among them, the Bilocal model is the simplest and most studied quantum network, that is, two independent entanglement sources allocate entanglement to three observers, similar to the entanglement exchange scenario, the intermediate node receives two particles and makes a Belky measurement so that the entire network has a non-local association.

However, the previously defined non-locality of the network cannot characterize the non-canonicality of all sources in the entire network, and in most cases can degenerate into a violation of the standard Bell inequality, and intermediate nodes do not need to use entanglement measurements. Therefore, physicists propose the concept of network-wide non-locality, which requires all sources in the network to distribute non-classical resources that can be used to authenticate the non-classical nature of the network’s full connection. At present, the non-locality of the whole network is only tested in the simplest bilocal model.

In this work, the research group achieved breakthroughs in theory and experiment, and successfully verified the non-locality of the whole network in more complex star networks. Theoretically, the research group proposes a new network-wide non-local criterion under the condition that only independent source and signal-free principles are used without requiring the network to follow the principles of quantum mechanics. In the experiment, the research group used a high-quality “sandwich” type entangled light source to build a star network with three peripheral nodes, and realized high-quality GHZ state projection measurement at the central node.

According to the researchers, the experimental results violate the non-local criterion of the whole network at a level of more than 10 standard deviations. This is the first verification of the non-local nature of the whole network in a complex network, which is of great significance for the application of large-scale quantum networks, especially in the security assurance of quantum communication protocols. (Source: Wang Min, China Science News)

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