Modelling efficient BB84 with applications for medium-range, terrestrial free-space QKD

Terrestrial free-space quantum key distribution is ideally suited for deployment in dense urban environments. The transition from laboratory to commercial deployment, however, raises a number of important engineering and issues. Here, we investigate these issues efficient BB84 using weak coherent pulse-decoy state protocol. We calculate expected lengths different environmental conditions when the scope optimisation protocol parameters restricted due practical considerations. In particular, find that fixed receiver basis choice probability, it can be advantageous allow transmitter have probability depending on varying channel loss background light levels. Finally, examine effects pulse intensity uncertainty finding they dramatically reduce length. These results used determine budget optics QKD systems assist their design.