In the experiment shown here, pairs of photons are generated. To do this, a laser beam (1) is split in a special crystal (2) so that two photons with half the energy are generated from each photon. These photons are deflected to the left and right (3) and sent through two rotatable polarisation filters (4,5). Two detectors are used (6,7) to prove that both photons of a pair are present.

Please click "more" on the bottom of this page for an explanation of polarisation.