Free-Space Decoy-State Quantum Key Distribution

Quantum cryptography, the only method which can provide quantifiable security of a distributed key, became the first application of quantum information methods. Complementary to fiber based systems, free space optics enables one to establish a secure key in various new scenarios,e.g., authentication to money machines or short distance links in metropolitan areas. Here we report on secure communication over 144 km between the islands of Tenerife and La Palma. Decoy state analysis ensured the security of our attenuated pulse scheme for a link efficiency of about 35 dB and resulted in key rates of 231 bit/s, clearly demonstrating the feasibility of free space links to satellites enabling global secure key exchange.