A class of Bell diagonal entanglement witnesses in ${\mathbb{C}}^4\otimes {\mathbb{C}}^4$: optimization and the spanning property

Abstract

Two classes of Bell diagonal indecomposable entanglement witnesses in ${\mathbb{C}}^4\otimes {\mathbb{C}}^4$ are considered. Within the first class, we find a generalization of the well-known Choi witness from ${\mathbb{C}}^3\otimes {\mathbb{C}}^3$, while the second one contains the reduction map. Interestingly, contrary to ${\mathbb{C}}^3\otimes {\mathbb{C}}^3$ case, the generalized Choi witnesses are no longer optimal. We perform an optimization procedure of finding spanning vectors, that eventually gives rise to optimal witnesses. Operators from the second class turn out to be optimal, however, without the spanning property. This analysis sheds a new light into the intricate structure of optimal entanglement witnesses.

arXiv comment15 pages, 1 figure

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• On the structure of mirrored operators obtained from optimal entanglement witnesses
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• A mirrored pair of optimal non-decomposable entanglement witnesses for two qudits does exist
• Mirrored Entanglement Witnesses for Multipartite and High-Dimensional Quantum Systems
• Detecting Entanglement by State Preparation and Local Measurements