Mohd Fared Abdul Khir,Mohd Fared Abdul KhirMazainun A. Mohd Zain,Mazainun A. Mohd ZainSuhairi Saharudin,Suhairi SaharudinSuryadi Soekardjo,Suryadi SoekardjoSahbudin Bin Haji Shaari2024-05-282024-05-28201218/1/2021Mohd Fared Abdul Khir, Mazainun A. Mohd Zain, Suhairi Saharudin, Suryadi Soekardjo, and Sahbudin Bin Haji Shaari "Implementation of two-way free space quantum key distribution," Optical Engineering 51(4), 045006 (9 April 2012). https://doi.org/10.1117/1.OE.51.4.0450060091-32862444-8https://doi.org/10.1117/1.OE.51.4.045006https://www.spiedigitallibrary.org/journals/optical-engineering/volume-51/issue-4/045006/Implementation-of-two-way-free-space-quantum-key-distribution/10.1117/1.OE.51.4.045006.short?SSO=1https://oarep.usim.edu.my/handle/123456789/4468We report an implementation of a two-way, four-state quantum key distribution (QKD) protocol (namely, the LM05 protocol) over a free space medium. A stable quantum bit error rate of 3.34% and maximum tolerable channel loss for secure key generation of 5.68 dB in the absence of a photon number splitting attack were recorded. The result strongly indicates the feasibility of a two-way QKD protocol implementation over a free space medium.en-USArticle17514