Quantum Cryptography with Optical Entanglement at 1.5 µm
Alexander V. Sergienko, Martin A. Jaspan, Bahaa E. A. Saleh, Malvin Carl Teich · Frontiers in Optics · 2006
We report on the engineering, preparation, and utilization of polarization entangled-photon states in the telecommunications window of 1.5 µm for secure quantum key distribution. Traditionally, such sources have been based on the use of the process of spontaneous parametric down conversion (SPDC) when nonlinear crystal is pumped by a continuous wave (cw) or a pulsed laser. The pump photon disintegrates spontaneously giving birth to two twin photons that are strongly correlated in frequency, polarization and wave vector (direction of propagation). Photon entanglement results from the fact that the possible values of correlated parameters of twin photons are made indistinguishable from each other either at the generation or at the single-photon detection stage. This leads to non-classical interference effects.