Abstract

We report on the development and long-term field testing of a free-space quantum key distribution (QKD) system based on phase–time encoding, adapted from a commercially available fiber-based platform (ViPNet QTS). The system was deployed over a 400 m urban atmospheric optical link between two buildings of Lomonosov Moscow State University, employing a multimode free-space Michelson interferometer for robust phase-state analysis under atmospheric turbulence. Stable secret key generation at rates of several hundred bits per minute with a quantum bit error rate of ~4.2% was achieved over multiple hours and repeated days, demonstrating autonomous operation and resilience to environmental fluctuations. Dispersion effects were found negligible, confirming the suitability of the multimode reception scheme. Ongoing efforts focus on achieving continuous daylight operation, critical for practical deployment. The results indicate that this minimally modified fiber-based platform provides a promising approach for urban free-space quantum communication networks.

Biography

Vladislav Tretiakov, 25, received his MSc with distinction from Moscow State University in 2024 and is currently a PhD student at the Faculty of Physics, MSU. He is a research associate at the Quantum Technology Centre, MSU, and has published 2 peer-reviewed articles while presenting his work at 6 international conferences in quantum communication and quantum cryptography.