We demonstrate the experimental violation of a spin-1 Bell inequality. The spin-1 inequality is based on the Clauser, Horne, Shimony, and Holt formalism. For entangled spin-1 particles, the maximum quantum-mechanical prediction is 2.55 as opposed to a maximum of 2, predicted using local hidden variables. We obtained an experimental value of 2.27±0.02 using the four-photon state generated by pulsed, type-II, stimulated parametric down-conversion. This is a violation of the spin-1 Bell inequality by more than 13 standard deviations.
J. C. Howell, A. Lamas-Linares, and D. Bouwmeester, Experimental Violation of a Spin-1 Bell Inequality Using Maximally Entangled Four-Photon States, Phys. Rev. Lett. 88(3), 030401. https://doi.org/10.1103/PhysRevLett.88.030401
American Physical Society