Two-Color Parametric Down Conversion

We propose a point to point quantum channel based on a two-color Spontaneous Parametric Down Conversion (SPDC), that may be applied for a Quantum Key Distribution (QKD) system to gain better security. We use one arm of the SPDC (770 nm - optimal for Si detection) and a Si counter at Alice's side to count the exact number of photons in each pulse. Whenever the arm contains exactly one photon, the correlated photon (1550nm - optimal for fiber transmission) in the other arm is sent via a fiber to Bob.In the experiment we used an Ar+ laser of 514.5nm wavelength and a BBO crystal to produce type-I photon pairs. We measured the spectrum of the SPDC and resolved specifically the 770 nm wavelength. The rate of correlated pairs (at 890-1050 nm) from our SPDC source was compared to a non-correlated source. We further developed an InGaAs single photon detector based on Geiger mode APD and achieved 10% quantum efficiency and 5 (.) 10(-3) dark counts per 20nsec pulse at a temperature of -35 degrees C.