Quantum key distribution over a 2 km free-space channel with a high secure key rate

Abstract

Free-space quantum key distribution (QKD) provides crucial advantages, including mobility and deployment flexibility, for securing next-generation communication networks. However, practical free-space implementations face major challenges, such as muilti-photon vulnerabilities, spatial mode mismatch, and atmospheric turbulence-induced beam fluctuations. In this work, we experimentally demonstrate a free-space decoy-state BB84 QKD system operating at a 100 MHz repetition rate with a 2.5 ns pulse width over a 2 km outdoor channel. By employing an active beam-wander correction based on fast-steering mirrors (FSMs) and position sensitive detectors (PSDs) con?figuration, our system achieves a secure key rate of 164.8 kbps under a quantum bit error rate (QBER) of approximately 3.3 %. This demonstration provides a practical framework for deploying high-rate, long-distance free-space quantum communication in realistic turbulence environments.