Quantum key distribution

This thesis is indirectly related to the bachelor thesis Quantum key distribution over optical fiber infrastructure. Unlike the previous paper, the focus will be mainly on the practical application of the QKD (Quantum key distribution) system Clavis3. For this reason, physical phenomena related to practically used QKD protocols are briefly explained in the theoretical part. These are mostly based on phase coding. In particular, special attention is paid to the Coherent one-way protocol (COW) implemented in Clavis3 devices. This protocol is also compared with practical implementations of the BB84 protocol. Furthermore, the principles of other advanced QKD techniques are outlined and the phenomena in the optical fiber that may affect the quantum channel are discussed. A separate chapter is also devoted to standardization and topologies of QKD networks. Last but not least, the thesis addresses the topic of attacks against practical implementations of QKD protocols. In the practical part, measurements aimed at practical deployment of Clavis3 devices in a common communication network are performed. These include the possibility of combining a quantum channel into a single fiber together with classical channels using Wavelength-division multiplexing (WDM) and the analysis of the effect of Raman noise on the maximum communication distance. At the same time, the robustness of the system against polarization changes and fiber manipulation is verified. Finally, the performance of the system using three-state and four-state versions of the COW protocol is compared and the eavesdropping simulation module is tested