Free space quantum key distribution in daylight

Summary form only given. The Los Alamos free-space quantum key distribution (QKD) system operates at a 1-MHz clock rate. On each clock cycle a /spl sim/1-ns "bright timing pulse" is emitted from an array of /spl sim/1550-nm lasers at the transmitter ("Alice"). After a /spl sim/100 ns delay one of four temperature-controlled "data" diode lasers emits a /spl sim/1-ns, 772-nm optical pulse that is attenuated to the single-photon level. We present results from operations over multi-kilometer atmospheric ranges. The spectral, spatial and temporal filtering allow practical secret bit rates even in full daylight. We also present a study of a satellite-to-ground QKD system, and an analysis of the expected secret bit rate.