Improve the Maximum Transmission Distance of Four-State Continuous   Variable Quantum Key Distribution by using a Noiseless Linear Amplifier
  A modified four-state CVQKD protocol is proposed to increase the maximum transmission distance and tolerable excess noise in the presence of Gaussian lossy and noisy channel by using a noiseless linear amplifier (NLA). A NLA with amplitude gain g can increase the maximum admission losses by 20log(g) dB. 
Bingjie Xu, Chunming Tang, Hui Chen, Wenzheng Zhang, and Fuchen Zhu
quant-ph