Homodyne characterization of continuous variable bipartite states

We suggest a scheme to reconstruct the covariance matrix of continuous variable two-mode states using a single homodyne detector and a few polarization elements. Our method can be used to fully characterize the bipartite Gaussian entangled states obtained at the output of a (nondegenerate) optical parametric amplifier driven below threshold, as well as to extract relevant informations on generic bipartite states made of two frequency degenerate but orthogonally polarized modes.