I suspect I have at least some friends who may have used an optical setup that uses the spontaneous parametric down-conversion process to produce entangled photons. Those photons can then be put into a Mach-Zehnder interferometer and provide the statistical basis for the verification of quantum entanglement and non-locality. (Bell Inequality)

It is a cool experiment that I would like to reproduce myself. Modern FPGAs make the coincidence detection pretty easy, and the optical parts are reasonable to obtain. Using a 405nm laser source and a correctly cut a beta-barium borate crystal would net some coupled photons at 810nm, which is something detectable with fiber-coupled detectors.

Anyone built one of these before?