Abstract

In the famous and mind-boggling experiments by Zhou et al. and Wang et al. [1–3] it has been shown that spatially separated two photon sources based on spontaneous parametric down conversion can be coupled coherently by induced coherence without stimulated emission. This has been accomplished by overlapping the idler beam of the first crystal with the idler beam of the second, preventing the possibility of telling the signal photons originating in different crystals from each other based on the observation performed on the idler beams. Recently the effect of induced coherence was used successfully in an imaging setup [4] where the photons illuminating the object were not detected. Although this effect is now transferred to a practical application, it is still a source of fundamental questions concerning the interplay of coherence and indistinguishability of two photon states [5, 6].

© 2015 IEEE