Polarisation correlation in the two-photon decay of metastable atomic deuterium and a test of Bell's inequality

Abstract

A 1-keV metastable atomic deuterium [D(2S)] beam of density about 104 atoms cm-3 has been produced by charge-exchange, in caesium vapour, of deuterons extracted from a radio-frequency ion source. The linear and circular polarisation correlation of the two photons emitted spontaneously by metastable atomic deuterium in a true second order radiative process have been measured for the first time. While the circular polarisation results confirm the conservation of angular momentum along the common axis of detection, the correlation in linear polarisation has been applied in a test of Bell’s Inequality which allows a quantitative distinction to be made between the predictions of Quantum Mechanics and local realistic ("hidden variable") theories. The results are in agreement with Quantum Mechanics and violate Bell’s Inequality by almost two standard deviations.