Abstract
We present a criterion that determines whether a fermionic state is a convex combination of pure Gaussian states. This criterion is complete and characterizes the set of convex-Gaussian states from the inside. If a state passes a program it is a convex-Gaussian state and any convex-Gaussian state can be approximated with arbitrary precision by states passing the criterion. The criterion is presented in the form of a sequence of solvable semidefinite programs. It is also complementary to the one developed by de Melo, Ćwikliński, and Terhal, which aims at characterizing the set of convex-Gaussian states from the outside. Here we present an explicit proof that criterion by de Melo et al. is complete by estimating a distance between an -extendible state, a state that passes the criterion, to the set of convex-Gaussian states.
- Received 9 October 2014
DOI:https://doi.org/10.1103/PhysRevA.90.062329
©2014 American Physical Society