Testing of quantum key distribution system in urban fiber-optic communication lines

The features of working on real city lines of a complex of quantum cryptographic information protection equipment, developed by InfoTeCS in conjunction with Lomonosov Moscow State University. The system was tested both in stable external conditions and in the presence of a temperature gradient. It was noted that a temperature change from +25 to +18 °C caused a twofold increase in quantum errors and, consequently, a decrease in the secret key rate, but did not lead to a complete stop of secret key generation. According to test results direction of future work and ways to improve the quality of quantum key distribution system are developed.