The security of data has never been more valuable. Today, cryptography is critical to the safe operation of digital infrastructures. However, yearly advances in quantum computing present new threats. Quantum Key Distribution (QKD) may provide the best protection, an approach designed to ensure privacy using quantum information encoded on photons. In theory, QKD is proven secure. In practice, QKD systems deviate from this theoretical behaviour due to implementation. Currently, QKD requires a separate dark fibre due to its susceptibility to classical channel effects (e.g. noise, Kerr non-linear interference, and scattering effects). Separating QKD from classical optical signals is costly and impractical, keeping QKD a niche product. Therefore, network providers seek quantum security to coexist with existing classical optical infrastructure. A better understanding of a quantum/classical optical channel is needed to develop improved channel coding, robust error-correcting schemes, digital signal processing, and optoelectronic components for the transceivers. In addition, a study on network topologies and integrating classical to quantum signals on implementation security is needed. The doctoral research network - QuNEST aims to gather diverse industrial and academic partners with strong scientific and technical expertise in QKD technology and optical communications to establish a new, innovative, multi-disciplinary, training network for doctoral researchers (DR). The high-level objective is to train experts to design, develop, and drive the future of quantum secure optical infrastructures. This doctoral network currently trains 11 Doctoral Candidates, leaning on the expertise of 17 partners: 6 universities, and 11 Industrial partners (i.e. 1 Simulation software provider, 2 Telecom operators, 2 SMEs and 6 hardware vendors). From 7 European countries, QuNEST provides a unique and timely opportunity to train students in quantum physics and optical communications
