Yh. Shih et Av. Sergienko, A 2-PHOTON INTERFERENCE EXPERIMENT USING TYPE-II OPTICAL PARAMETRIC DOWN-CONVERSION, Physics letters. A, 191(3-4), 1994, pp. 201-207
A pair of orthogonally polarized light quanta, produced from type II p
arametric down conversion, is injected into a single input port of a b
eamsplitter and detected coincidently by two detectors placed in the t
wo output ports of the beamsplitter. With the help of a set of crystal
quartz plates, a Pockel's cell and two linear polarizers, the coincid
ence counting rate exhibits interference modulation of the pump freque
ncy with 88% visibility when manipulating the voltage across the Pocke
l's cell, regardless of the optical delay (which is much greater than
the coherence length) and the mutual incoherence. This two-photon inte
rference effect is responsible by a nonclassical two-photon state whic
h is entangled both in spin and in space-time.