Characterization of bipartite states using a single homodyne detector
  We suggest a scheme to reconstruct the covariance matrix of a two-mode state using a single homodyne detector plus a polarizing beam splitter and a polarization rotator. It can be used to fully characterize bipartite Gaussian states and to extract relevant informations on generic states. 
Virginia D'Auria, Alberto Porzio, and Salvatore Solimeno, Stefano   Olivares, Matteo G.A. Paris