  We investigate a decoy-state quantum key distribution (QKD) scheme with a
sub-Poissonian single-photon source, which is generated on demand by scattering
a coherent state off a two-level system in a one-dimensional waveguide. We show
that, compared to coherent state decoy-state QKD, there is a two-fold increase
of the key generation rate. Furthermore, the performance is shown to be robust
against both parameter variations and loss effects of the system.
