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 Celsius.
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