File:Quantum entanglement vs classical correlation video.gif

English: This video demonstrates the difference between entangled and classically correlated quantum states when the polarization of photons is considered. In the scene on the left, the source produces photon pairs in a singlet state, which is maximally entangled. In the scene on the right, the photon pairs are created in a dephased singlet state, which is mixed and only classically correlated. In both scenes, there is a source of photon pairs in the center. One photon of each pair propagates to the detection station on the left and its partner photon propagates to the detection station on the right. Each detection station consists of a polarizing beam splitter and two detection screens. The detection stations can measure the polarization of incoming photons in different linearly-polarized bases. The video comprises three parts. In the first part, the photons are measured in the H/V basis. Both entangled and classically correlated states give rise to the same measurement results (up to random fluctuations that are intrinsic to the quantum measurements). In the second part, the measurements are performed in different bases, where the difference between the two states becomes apparent. In the third part, only the probabilities of photon detections are plotted and the detection stations are rotated smoothly over the entire range of linear polarizations. Even though the probabilities for the classically correlated state vary as the rotation angle increases, the probabilities for the entangled singlet state remain constant.