Abstract

Quantum cryptography – or quantum key distribution (QKD) [1] – was the first application of the evolving field of quantum information technology to become commercially available. The maximum distance for QKD in practical applications, however, is currently limited by the noise of available single photon detectors and the absorption along the quantum channel, for example, in fiber to about 100 km. In principle, this problem can be overcome by subdividing a larger distance into smaller segments and employing a quantum repeater scheme. Yet, this is still far beyond state-of-the-art technology. In the meantime, a network of trusted nodes connected by fiber or short free-space links is one option for bridging longer distances. Alternatively, a free-space link from a low-earth-orbit (LEO) satellite to a ground station could be used. By exchanging quantum keys between the satellite and different ground stations consecutively, one can easily establish a secret key between any two ground stations worldwide, thereby enabling truly global quantum key distribution.

© 2007 IEEE