  Quantum properties are soon subject to decoherence once the quantum system
interacts with the classical environment. In this paper we experimentally test
how propagation losses, in a Gaussian channel, affect the bi-partite Gaussian
entangled state generated by a sub-threshold type-II optical parametric
oscillator (OPO). Experimental results are discussed in terms of different
quantum markers, as teleportation fidelity, quantum discord and mutual
information, and continuous variables (CV) entanglement criteria. To analyse
state properties we have retrieved the composite system covariance matrix by a
single homodyne detector. We experimentally found that, even in presence of a
strong decoherence, the generated state never disentangles and keeps breaking
the quantum limit for the discord. This result proves that the class of CV
entangled states discussed in this paper would allow, in principle, to realize
quantum teleportation over an infinitely long Gaussian channel.
