Use of parametric down-conversion to generate sub-Poissonian light

Abstract
Two highly noise-correlated light beams are generated by nondegenerate parametric down-conversion. We report the production of sub-Poissonian light in one of the beams by using negative feedback (to the pump) from the other. This nonclassical light source has a postdetection Fano factor of 0.78 over a limited frequency range near 50 Hz with an intensity of about 60 pW.