Simulation of "Entangled photons, nonlocality and Bell inequalities in the undergraduate laboratory"
This experiment simulates the experiment done in: http://arxiv.org/pdf/quant-ph/0205171v1.pdf
Author: Hannes Landeholm hannes@jumpstarter.io
The experiment is interesting because results in a bell inequality violation which proves that a local hidden variable explanation to QM is impossible unless you violate special relativity by introducing super luminal information transfer (which makes the HVT pointless as it's original purpose in the EPR paper was to remove an incompatibility between QM and SR).
"A 5 mW freerunning InGaN diode laser produces a beam of violet (405 nm) photons which pass through a blue filter, a linear polarizer, and a birefringent plate before reaching a pair of beta barium borate (BBO) crystals." The crystals are placed face to face. Crystal #1 is rotated 0 degrees in relation to the polarization of the laser while the crystal #2 is rotated 90 degrees in respect to it. The crystals allow the possibility of Type-I spontaneous parametric down-conversion (SPCD). The reason why the photons are split are not understood at a fundamental level but irrelevant to the purpose of the experiment. When SPCD occurs in one of the crystals the two resulting photons will be emitted at a random angle in a "cone trajectory" where each photon has a relative 180 degree angle in respect to each other. The emitted photons is ordinary polarized relative to the axis of the crystal that generated them. The crystals are 0.1 mm thick and the beam itself is 1 mm thick. This makes the crystals thin enough that the resulting SPDC light cone from each crystal almost completely overlaps. This erases the information of which crystal the SPDC originated from (the which-path information) making it impossible to know the polarization from measuring the photon position alone. Therefore the light cones are in a superposition of polarization states. We can find entangled photon pairs at any points around the cone, opposite of each other with correlating polarization.
Licence: MPLv2