Improving the maximum transmission distance of continuous-variable   quantum key distribution using a noiseless amplifier
  We show that the maximum transmission distance of continuous-variable quantum key distribution in presence of a Gaussian noisy lossy channel can be arbitrarily increased using a linear noiseless amplifier. We explicitly consider a protocol using amplitude and phase modulated coherent states with reverse reconciliation. We find that a noiseless amplifier with amplitude gain g can increase the maximum admissible losses by a factor 1/g^2. 
R\'emi Blandino, Anthony Leverrier, Marco Barbieri, Jean Etesse,   Philippe Grangier and Rosa Tualle-Brouri
quant-ph