Towards practical quantum cryptography

Quantum cryptography bases the security of quantum key exchange on the laws of quantum physics and is likely to become the first application employing quantum effects for communication. Here we present performance tests of a new design based on polarization encoding of attenuated, coherent light pul ses. Our measurements show that this compact setup can achieve an effective key-bit rate in the kHz range with low alignment requirements and thus off ers the tools for fast and user-friendly quantum key exchange.