Researchers certify true device-independent multiparty entanglement

Teacher. Li Chuanfeng, Prof. Huang Yunfeng, Prof. Chen Geng, and their colleagues from the group of Prof. Guo Guangcan at the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), in collaboration with Swiss academicians, certified for the first time a true device-independent multiparty entanglement and have invented a new method to certify true multiparty entanglement without making any assumptions about the inner workings of the measuring device. Their work has been published in Physical examination letters.

Authentic multiparty entanglement is considered the most powerful form of entanglement and an essential resource for quantum information processing. The complete knowledge of system dimensions and precise calibrations of measuring instruments that are necessary to detect true multipartite entanglement are usually difficult to acquire in an experiment.

In principle, the entanglement properties of a system can be tested using device-independent measurements and analyzing the violation of Bell’s inequality in the measurement results without making assumptions about the system. However, certification of true device-independent multipartite entanglement in an arbitrary finite dimension remains a challenge due to the difficulty in identifying optimal multipartite Bell inequalities.

By decomposing the internal structure of the multiparty system, the researchers delimited the minimum covering sets and the full covering sets, respectively. They then applied Bell’s bipartite inequality to examine the multiparty entanglement system. This method could certify true multipartite entanglement in arbitrary sizes and shapes using only the Clauser-Horne-Shimony-Holt (CHSH) inequality. It could also measure the weight of true multiparty entanglement within multiparty entanglement.

The researchers experimented on entangled four-photon states, and the results showed that full coverage is very noise tolerant and minimum coverage can achieve higher efficiency while being robust to noise, i.e. say that the number of measuring devices is not growing exponentially. with the size of the system. Several vital forms of multipartite entangled states were examined, and measurements of the two coverings proved the existence of true multipartite entanglement. The weights of genuine multipartite entanglement in different forms were also calculated.

More importantly, the researchers examined a weakly entangled state that was found to be unable to violate the standard multipartite Bell’s inequality, which previously made it difficult to determine its true entanglement properties by device-independent methods. . But in this work which used the new structure decomposition method, such weakly entangled states violated the local limit and were confirmed to be true multipartite entanglement.