Quantum characterization of bipartite Gaussian states

TL;DR

This paper presents a robust, experimentally demonstrated method for fully characterizing bipartite Gaussian states using a single homodyne detector, enabling detailed analysis of quantum optical states for quantum information applications.

Contribution

The paper introduces a new reliable method for complete bipartite Gaussian state characterization with a single homodyne detector, including advanced Gaussianity tests and physical quantity retrieval.

Findings

Successful application to entangled CW beams from a sub-threshold optical parametric oscillator

Reliable reconstruction of covariance matrix and physical properties

Method includes Gaussianity tests and state analysis

Abstract

Gaussian bipartite states are basic tools for the realization of quantum information protocols with continuous variables. Their complete characterization is obtained by the reconstruction of the corresponding covariance matrix. Here we describe in details and experimentally demonstrate a robust and reliable method to fully characterize bipartite optical Gaussian states by means of a single homodyne detector. We have successfully applied our method to the bipartite states generated by a sub-threshold type-II optical parametric oscillator which produces a pair of thermal cross-polarized entangled CW frequency degenerate beams. The method provide a reliable reconstruction of the covariance matrix and allows to retrieve all the physical information about the state under investigation. These includes observable quantities, as energy and squeezing, as well as non observable ones as purity, entropy and entanglement. Our procedure also includes advanced tests for Gaussianity of the state and, overall, represents a powerful tool to study bipartite Gaussian state from the generation stage to the detection one.