Estimating the Degree of Entanglement of Unknown Gaussian States
  We give an introduction to Gaussian states and operations. A discussion of the entanglement properties of bipartite Gaussian states in terms of its covariance matrix follows. It is explained how entanglement can be witnessed using feasible measurements, e.g. homodyne measurements. We find that the outcome of such a measurements cannot only witness but also quantify entanglement. 
Janet Anders