Quantum key distribution over 122 km of standard telecom fiber

We report the first demonstration of quantum key distribution over a standard telecom fiber exceeding 100 km in length. Through careful optimisation of the interferometer and single photon detector, we achieve a quantum bit error ratio of 8.9% for a 122km link, allowing a secure shared key to be formed after error correction and privacy amplification. Key formation rates of up to 1.9 kbit/sec are achieved depending upon fiber length. We discuss the factors limiting the maximum fiber length in quantum cryptography

Barbosa et al. Reply to ``Comment on 'Secure Communication using mesoscopic coherent states', Barbosa et al, Phys Rev Lett 90, 227901", Yuan and Shields, Phys. Rev. Lett. 94, 048901(2005)

Yuan and Shields claim that our data-encryption protocol is entirely equivalent to a classical stream cipher utilizing no quantum phenomena. Their claim is, indeed, false. Yuan and Shields also claim that schemes similar to the one presented in Phys. Rev. Lett. 90, 227901 are not suitable for key generation. This claim is also refuted. In any event, we welcome the opportunity to clarify the situation for a wider audience.Comment: This is the co-published Reply to the Comment made by Z.L. Yuan and A.J. Shields published in Physical Review Letters, 94 (2005