Phase-compensated ultra-bright source of entangled photons

While the most direct method to increase the brightness of a type-I entanglement source is to increase the collected solid angle of the down-conversion, this leads to effective decoherence caused by an angle-dependent phase shift. Using specially designed compensation crystals, we have reversed this effect and created the brightest source of entangled photons to date, over two million measured pairs per second, recorded while measuring the largest reported violation of Bell's inequality (1239 sigma).