Abstract

Free-space quantum key distribution (QKD) is expected to realized a global system for QKD based on a network of ground to satellite or satellite to satellite, and thus to extend the distance limit and the utility of QKD method [1]. We repot an experimental demonstration of free-space continuous-variable QKD (CV-QKD). We use a 1.55 μ m-wavelength pulsed diode laser and a pulsed homodyne detector. Advantages of working at 1.55 μ m over working at 0.8 μ m are that Rayleigh scattering in air is smaller and 1.55 μ m is eye safe. The homodyne detector is used to detect a faint light and it is sensitive only to the light that is spatially, temporally, and spectrally matched with the LO light. This means that the LO acts as a narrow filter. Therefore, a homodyne detector is less sensitive to a stray light compared with single-photon detector. In order to make a practical CV-QKD system using pulsed homodyne detection, realization of a stable interferometer is a necessary ingredient.

© 2007 IEEE