Continuous variable noise-free states in correlated quantum noisy   channels
  We explicitly compute the evolution of the density operator of a two-mode electromagnetic field when the influence of the thermal fluctuation of the vacuum is common for both modes. From this result, we give an example in which the bundle of quantum noisy channels turns out to be noiseless for the special type of signal states due to the correlation. 
Tohya Hiroshima, Osamu Hirota