Theoretical analysis of measurement-device-independent quantum key distribution systems integrated into fiber-optic communication lines using dense wavelength division multiplexing

Subject of study. The effect of noise resulting from spontaneous Raman scattering, four-wave mixing, and linear channel crosstalk on the performance of measurement-device-independent quantum key distribution systems with symmetric and asymmetric realizations is studied. Mathematical models of the measurement-device-independent quantum key distribution system and considered channel noise sources are presented. The secure key generation rate was calculated in all cases for assessment and subsequent analysis of the system performance. These results enabled the identification and presentation of the operation features of the measurement-device-independent quantum key distribution system upon its integration into existing fiber-optic communication networks using dense wavelength division multiplexing. Aim of the work. The performance of measurement-device-independent quantum key distribution systems integrated into fiber-optic communication lines using dense wavelength division multiplexing by means of numerical simulation is investigated. Method. An approach based on analysis of the Raman scattering cross section plot and allocation of the information channels of frequencies corresponding to areas located sideways to the pump wavelength was used to determine the optimal configurations of the allocation of quantum and information channels. A single-photon scheme in one symmetric and two asymmetric system realizations was considered for numerical simulations of the quantum key distribution system with an untrusted node. A security analysis was performed according to the Devetak–Winter bound that enables estimating the secure key generation rate in an asymptotic mode (for symmetric infinite sequences) in the presence of collective attacks in the quantum channel. Main results. It was confirmed that the implementation of measurement-device-independent quantum key distribution systems with equal paths of the sender and the receiver (i.e., symmetric) is optimal. The result deteriorated with an increase in the asymmetry parameter. If the quantum channel is within the C-band, the advantage of the symmetric realization was minimal, and it was almost indiscernible when the number of information channels was increased to 40. However, if the quantum channel was at the wavelength of 1310 nm (O band), the difference was significant. Moreover, allocation of the wavelength of 1310 nm to the quantum channel enables the longest distance of operation, and it weakly depends on the number of channels. Practical significance. For practical implementation of quantum key distribution systems, their integration into existing telecommunication infrastructure is of particular interest. This can be achieved through the simultaneous propagation of quantum and information channels in the fiber-optic communication lines by means of multiplexing, and in particular, dense wavelength division multiplexing. However, the power levels characteristic for quantum signals are significantly lower than those for information signals. Therefore, if the information and quantum channels propagate in the same fiber, the noise from the information channels significantly reduces the performance of the quantum key distribution systems. For this reason, the physical and mathematical description, analysis, and numerical simulation of the noise and its interaction with different quantum key distribution systems aimed at identifying the most effective integration method are crucial for the integration of quantum key distribution systems into existing telecommunication networks.