ABSTRACT
Since the first experiment of Bennett and Brassard [1], the experimental implementation of the BB84 is commonly performed using faint coherent pulses with about 0.1 to 0.4 photons per pulse (for a review see [2]). When using weak coherent pulses, the probability that a single pulse contains more than one photon is not zero. In quantum key distribution (QKD), this was seen for quite some time as a severe drawback as it limits the secure transmission distance [3].
