Finding decompositions of a class of separable states

TL;DR

This paper characterizes a specific class of separable quantum states with unique decompositions, providing an intrinsic description and a procedure to find these decompositions, which relate to quantum channels and separability criteria.

Contribution

It offers an intrinsic characterization and a constructive method for decomposing a class of separable states with independent image components, linking to facial structures and quantum channel types.

Findings

Decomposition with independent image components is unique.

States with rank matching a marginal rank are characterized.

The class includes states where PPT equals separability.

Abstract

By definition a separable state has the form \sum A_i \otimes B_i, where 0 \leq A_i, B_i for each i. In this paper we consider the class of states which admit such a decomposition with B_1, ..., B_p having independent images. We give a simple intrinsic characterization of this class of states, and starting with a density matrix in this class, describe a procedure to find such a decomposition with B_1, ..., B_p having independent images, and A_1, ..., A_p being distinct with unit trace. Such a decomposition is unique, and we relate this to the facial structure of the set of separable states. A special subclass of such separable states are those for which the rank of the matrix matches one marginal rank. Such states have arisen in previous studies of separability (e.g., they are known to be a class for which the PPT condition is equivalent to separability). The states investigated also include a class that corresponds (under the Choi-Jamio{\l}kowski isomorphism) to the quantum channels called quantum-classical and classical-quantum by Holevo.