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

TL;DR

This paper models efficient BB84 quantum key distribution for medium-range terrestrial free-space applications, addressing practical deployment issues, optimizing protocol parameters, and analyzing environmental effects to improve system design.

Contribution

It provides a detailed analysis of BB84 protocol performance under realistic conditions, including environmental factors and intensity uncertainties, guiding practical system development.

Findings

Optimal basis choice probabilities vary with channel loss and background light.

Pulse intensity uncertainty significantly reduces key length.

Environmental conditions impact expected key rates and system design.

Abstract

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