Gaussian Continuous-Variable Isotropic State.

Inspired by the definition of the non-Gaussian two-parametric continuous variable analogue of an isotropic state introduced by Mi\v{s}ta et al. [Phys. Rev. A, 65, 062315 (2002); arXiv:quant-ph/0112062], we propose a simple, but with respect to the correlation structure interesting example of a two-mode Gaussian analogue of an isotropic state. Unlike conventional isotropic states, which are defined as a convex combination of a thermal and an entangled density operator, our state is defined by a convex combination of the corresponding covariance matrices. This state is by construction Gaussian and can be understood as entangled pure state with additional Gaussian noise controlled by a mixing probability. Using various entanglement criteria and measures, we study the non-classical correlations contained in this state. Unlike the previously studied non-Gaussian isotropic state, the Gaussian state proposed here features a finite threshold in the parameter space where entanglement sets in.