Nonclassical Effects in Parametric Downconversion
In parametric downconversion the quantum effects arise because two photons are created from one pump photon. Detection of photons in one train can be used to modify the quantum statistics of the other train to produce antibunched and/or sub-poissonian light. This chapter reports on two experiments of this type. The first employs single photon detection techniques and a fast optical shutter to create antibunched and slightly sub-poissonian light. The second uses analogue detection and feedback to produce sub-poissonian light at picowatt power levels with a Fano factor of 0.78 over a limited bandwidth. Sub-poissonian light is potentially useful in finite dose transmission measurements and the high degree of temporal coincidence of the downconverted photon pairs can be exploited in absolute measurement of detector quantum efficiency. The detailed shape of the fourth order interference effect can be related to the fourier transform of the photon bandwidth determined by the phase matching uncertainty and aperture size.