Results of the NATO project: Analysis, design, and implementation of an end-to-end QKD link

This manuscript discusses the most relevant aspects of the practical implementation of a long-range Quantum Key Distribution (QKD) link with trusted nodes, achieving the highest possible secret key rate generation within the security and system-level constraints. To this purpose, the implementation of an end-to-end QKD system is described, including implementation aspects from the physical transmission of photon states through a standard telecommunications grade optical fiber, to consideration of quantum metrology and information reconciliation protocols based on forward error correction codes. In addition, since there are circumstances when a fiber optical link may not be available, we will also discuss the problems involved with the implementation of a Free Space Optics (FSO) QKD link. The manuscript also discusses the problem of information reconciliation in CV-QKD scenarios (both on fiber and FSO links), based on an Unequal Error Protection (UEP) reverse reconciliation scheme.