Abstract

At the beginning of the 80's Alain Aspect performed his well-known Bell-experiments (BE) on the non-locality of quantum mechanics, using a complicated two-photon source based on an atomic cascade transition. Since then such sources have been replaced by much simple devices consisting of a low power pump laser and a nonlinear crystal exploiting spontaneous parametric down conversion (PDC). Thanks to conservation of energy and momentum, this leads to energy-time entangled pairs of photons (signal and idler). Such sources are an essential tool for fundamental quantum optical experiments (BE, teleportation...) as well as for applied fields of research (quantum key distribution (QKD), metrology...).

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