Implementation of Two Way Free Space Quantum Key Distribution
  We report an implementation over free space medium of a two way four states quantum key distribution (QKD) protocol namely the LM05. The fully automated setup demonstrated a secure key generation rate of 3.54 kbits per second and quantum bit error rate (QBER) of 3.34% at mean photon number ({\mu}) = 0.15. The maximum tolerable channel loss for secure key generation considering Photon Number Splitting (PNS) attack, was 5.68 [dB]. The result successfully demonstrated the feasibility of a two way QKD protocol implementation over free space medium. 
M. F. Abdul Khir, M. N. Mohd Zain, Suryadi, S. Saharudin, S. Shaari
quant-ph