Secure communication using coherent states
  We demonstrate that secure communication using coherent states is possible. The optimal eavesdropping strategy for an M-ry ciphering scheme shows that the minimum probability of error in a measurement for bit determination can be made arbitrarily close to the pure guessing value P_e=1/2. This ciphering scheme can be optically amplified without degrading the security level. New avenues are open to secure communications at high speeds in fiber-optic or free-space channels. 
Geraldo A. Barbosa, Eric Corndorf, Prem Kumar, and Horace P. Yuen, G.   Mauro D'Ariano, Matteo G. A. Paris, and Paolo Perinotti