Secret key capacity of the thermal-loss channel: Improving the lower   bound
  We consider the secret key capacity of the thermal loss channel, which is modeled by a beam splitter mixing an input signal mode with an environmental thermal mode. This capacity is the maximum value of secret bits that two remote parties can generate by means of the most general adaptive protocols assisted by unlimited and two-way classical communication. To date, only upper and lower bounds are known. The present work improves the lower bound by resorting to Gaussian protocols based on suitable trusted-noise detectors. 
Carlo Ottaviani, Riccardo Laurenza, Thomas P. W. Cope, Gaetana   Spedalieri, Samuel L. Braunstein, Stefano Pirandola
quant-ph