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arXiv:1406.4954

Indecomposability of entanglement witnesses constructed from any permutations

Xiaofei Qi, Jinchuan Hou

Published Jun 19, 2014• 0 citations
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Abstract

Let $n\geq 2$ and $Φ_{n,t,π}: M_n({\mathbb C}) \rightarrow M_n({\mathbb C})$ be a linear map defined by $Φ_{n,t,π}(A)=(n-t)\sum_{i=1}^nE_{ii}AE_{ii}+t\sum_{i=1}^nE_{i,π(i)}AE_{i,π(i)}^†-A$, where $0\leq t\leq n$, $E_{ij}$s are the matrix units and $π$ is a non-identity permutation of $(1,2,\cdots,n)$. Denote by $\{{ F}_s: s=1,2\ldots, k\}$ the set of all minimal cycles of $π$ and $l(π)=\max\{\# { F}_s: s=1,2,\ldots,k\}$ the length of $π$. It is shown that the Hermitian matrix $W_{n,t,π}$ induced by $Φ_{n,t,π}$ is an indecomposable entanglement witness if and only if $π^2\not={\rm id}$ (the identity permutation) and $0

DOI
10.48550/arxiv.1406.4954

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We give an affirmative answer to the question posed by Yang et al. on the existence of indecomposable 2-positive linear maps from M3(C)\mathcal{M}_3(\mathbb{C})M3​(C) to M4(C)\mathcal{M}_4(\mathbb{C})M4​(C). In this study, we construct an explicit class of linear maps in B(M3(C),M4(C))\mathcal{B}(\mathcal{M}_3(\mathbb{C}), \mathcal{M}_4(\mathbb{C}))B(M3​(C),M4​(C)) that are positive, yet fail to be completely positive or completely copositive. Furthermore, we demonstrate that the associated Choi matrices of these maps serve as entanglement witnesses.