Quantum violation of Bell's inequality and its experimental test——on the Nobel Prize in Physics 2022

The Nobel Prize in Physics 2022 was awarded to Alain Aspect, John F. Clauser and Anton Zeilinger, for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science. Bell's inequality plays an indispensable role in the foundations of quantum mechanics and quantum information; its violation directly reveals the nonlocal nature of quantum mechanics.
Clarifying some basic concepts, this paper briefly introduces the establishment of Bell's inequality and the relevant research on its experimental verification. In order to solve the EinsteinPodolsky-Rosen (EPR) paradox, John S. Bell proposed his inequality according to D. Bohm's theory of localized hidden variables. He found that the results from quantum mechanics for such correlations violated the inequality and then displayed a "spooky" long-range quantum correlation even over space-like distances. This long-range correlation appears to have faster-than-light "action at a distance", which is simply due to the obvious or potential use of the "wave-packet collapse" postulate. The EPR paper explicitly used this assumption to infer the physical reality elements of distant objects, thus questioned the completeness of quantum mechanics. We review the groundbreaking experiments on the violation of Bell's inequality conducted by Aspect, Clauser and Zeilinger, then furthermore recall the foundational contributions of Chinese physicists in creating entangled states and testing the violation of Bell's inequality. In an early pioneering experiment, Chien-Shiung Wu et al utilized positron annihilation to generate EPR photons; TsungDao Lee and Chen-Ning Yang proposed that generating two neutral K-mesons K⁰-\rm\bar K⁰ to create EPR states; Yanhua Shih, Zhe-Yu Ou, Kun-Chi Peng, and others used various nonlinear optical crystals, including those discovered by Chuang-Tian Chen et al, to generate entangled photon pairs.