Quantum mechanics and polarization correlations for photons

J. W. de Roever, Martin Streng

Kurt Jung

Since John Bell has established his famous inequality and several independent experiments have confirmed the distinct polarization correlation of entangled photons predicted by quantum mechanics it is evident that quantum mechanics cannot be explained by local realistic theories. Actually, the observed polarization correlation can be deduced from wave optical considerations. The correlation has its origin in the phase coupling of the two circularly polarized wave packets leaving the photon source simultaneously. The experimental results violate Bell's inequality although no non-local interactions have to be assumed. In consequence the principle of locality remains valid in the scope of quantum mechanics. However, the principle of realism has to be replaced by the less stringent principle of contextuality.

Alfredo Luis

Alan J. Duncan, H. Kleinpoppen, Z. A. Sheikh

The Paper first summarizes fundamental aspects and results of the quantum electrodynamical theory of the two-photon radiationfromthe decay of the metastable 2 2 S 1/2 atomic hydrogen state. After a brief description of the second improved Stirling two-photon coincidence experiment polarization correlations of the two-photon decay are described in which both two or three linear polarizers are applied in order to test predictions of such correlations based upon quantum mechanics and local realistic theories (i.e., Einstein-Podolsky-Rosen type experiments). It is particularly noticeable that the three-polarizer coincidence measurement provided the largest difference (about 40%) between the Bell limits of local realistic theories and quantum mechanics so far. Apart from confirming in addition the correlations of right-right and left-left circularly polarized two-photon correlations a new type of coherence analysis of the two-photon radiation has been carried out experimentally and theoretically. A result of it is the measured coherence time of τ coh = 1.2 · 10 −15 s and coherence length of l coh = c · τ coh = 350 nm of the two-photon emission. By applying a theoretical model of the two-photon radiation linked to cascade transitions the coherence length can be estimated to l coh ≈ 100 nm in agreement by order of magnitude with the experimental data.

Giuseppe Faraci, A. Pennisi

T. Haji-Hassan, Alan J. Duncan, Walter Perrie +2 more

Measurements have been made of the polarization properties of the two photons emitted in the decay of metastable atomic deuterium in an experiment in which three linear polarizers, instead of the normal two, are used. The quantum-mechanical predictions for these imperfect polarizers have been calculated and shown to be in good agreement with the experimental results. The results have also been used to test local realistic models which are capable of explaining all existing two-polarizer-type experiments, and have provided conclusive evidence against these theories.