Practical quantum cryptography in free space
W. T. Buttler, Richard Hughes, Paul G. Kwiat, S. K. Lamoreaux, G. G. Luther, George L. Morgan, J. E. Nordholt, Charles G. Peterson, Charles M. Simmons, Andrew G. White · 2002
Summary form only given.We demonstrated quantum cryptography, or quantum key distribution (QKD), in free space over an outdoor optical path of /spl sim/950 m under nighttime conditions. The success of free space QKD against a high background depends on the transmission and detection of single photons through an optically thick and turbulent medium. It has been shown that a combination of sub-nanosecond timing, narrow filters, spatial filtering, and adaptive optics can render the difficult detection problem tractable. Further, the nonbirefringent nature of the atmosphere at optical wavelengths allows the transmission of the single photon polarization states used in the free-space QKD protocol.