Dim Coherent States as Signal States in the Bb84 Protocol: Is it Secure?
Norbert Lütkenhaus · Kluwer Academic Publishers eBooks · 2005
Practical realizations of quantum key distribution employ dim coherent states as an approximation to single photon states. The advantage is that dim coherent states are convenient to use. The draw-back is that the security proofs for quantum key distribution have to be adapted. Difficulties arising from the use of signal states containing multi-photon contributions in combination with lossy channels have been pointed out earlier by Huttner et al. 1 . In this paper I describe a first numerical bound allowing quantum key distribution using dim coherent signal states in the presence of noise.