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.