Contents I. Introduction
Quantum Key Distribution (QKD) constitutes a promising solution for ensuring secure communication by leveraging the fundamental principles of quantum mechanics to exchange cryptographic keys, offering unparalleled security [1]. Recent advances in QKD research have focused on developing practical and efficient QKD systems that can be integrated into existing telecommunications infrastructure. One of the first field experiments has been demonstrated in Tokyo QKD network in 2010 [2], where the supported applications included secure video conferencing and an interface to secure mobile phone devices while South Korean Telecom deployed, in 2016, a Discrete-Variable (DV)-QKD system to fortify its Long-Term Evolution (LTE) network in Sejong City in South Korea [3]. Moving towards larger-scale QKD networks, the field operation of a 46-node quantum metropolitan area network has been recently demonstrated in city of Hefei, showing the potential of QKD technology to support service encryption in large-scale networks [4]. Dynamic QKD networking providing end-to-end quantum secured 5G services has also been demonstrated in Bristol [5], verifying the capability of QKD nodes to support inter-domain services in a fully virtualized network. Aside from the above fully operational QKD networks, British Telecom (BT) labs have recently reported an impressive collaboration between QKD and Post-Quantum Cryptography (PQC) technologies which allow the creation of 5G network slices with different encryption requirements [6]. Toshiba and BT labs have recently demonstrated a field trial for Industry 4.0 applications [7], showing the seamless integration of a QKD network into a smart manufacturing environment pursued in the 5G and beyond connectivity. Encryption services for quantum-safe 5G networks have been also considered within Madrid QCI which hosts QKD links in a multi-node physical infrastructure [8].
