Comparative Cost Analysis of Prepare and Measure and Entanglement-Based QKD Networks

We investigate, for the first time, the important research question of which quantum key distribution (QKD) protocol, prepare and measure (P&M) or entanglement based (EB), is more cost-effective in optically switched metropolitan quantum networks without quantum repeaters. To do so, we i) formulated novel integer linear programming (ILP) models aimed to minimise the cost to deploy PM and EB QKD networks whilst achieving a target quantum key exchange rate and ii) applied the ILP models to determine the minimum cost configuration of both types of QKD networks in two cases of study. Our findings suggest that, depending on the cost and technical specifications of network components as well as the target key rate performance, there are clear regimes for which one protocol offers improved costs with respect to the other. For example, in the cases studied we found that PM-QKD is preferred as long as the single-photon sources used in PM-QKD are half the cost of the entangled photon sources used in EB-QKD. In contrast, EB-QKD is more cost-effective when the cost of the sources is similar, but the cost of the detectors is low and EB-QKD can exploit multiple channels to exchange keys.