Retrieving the covariance matrix of an unknown two-mode Gaussian state by means of a reference twin beam

• A method for revealing the covariance matrix of a general two-mode Gaussian state is suggested.
• Twin beams are used as a reference.
• The method uses three beam splitters and four detectors measuring in coincidence.

A method for revealing the covariance matrix of an unknown two-mode Gaussian state is given based on the interference with a reference twin beam whose covariance matrix is known. In the method, first- and second-order cross-correlation intensity moments are determined varying the overall phase of the reference twin beam.