Developments towards practical free-space quantum cryptography
P. R. Tapster, P.M. Gorman, David M. Benton, D.M. Taylor, Brian S. Lowans · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2005
We describe a free space Quantum cryptography system which is designed to allow continuous unattended key exchanges for periods of several days, and over ranges of a few kilometres. The system uses a four laser faint pulse transmission system running at a pulse rate of 10MHz to generate the required four alternative polarization states. The receiver module similarly automatically selects a measurement basis and performs polarization measurements with four avalanche photodiodes. The controlling software can implement the full key exchange including sifting, error correction, and privacy amplification required to generate a secure key.