Polarization Correlation of the Two Photons Emitted by Metastable Atomic Deuterium: A Test of Bell's Inequality

Abstract
The polarization correlation of the two photons emitted simultaneously by metastable atomic deuterium in a true second-order decay process has been measured for the first time. The results are in agreement with quantum mechanics and violate Bell's inequality by nearly 2 standard deviations in an experiment where the process of absorption and reemission is not important.