# Questions tagged [entanglement-witness]

In quantum information theory, an entanglement witness is a functional which distinguishes a specific entangled state from separable ones. (Wikipedia)

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### Finding a class $C$ of bipartite PPT states such that entanglement of $\rho \in C$ implies entanglement of $\rho + \rho^{\Gamma}$

Consider an entangled bipartite quantum state $\rho \in \mathcal{M}_d(\mathbb{C}) \otimes \mathcal{M}_{d'}(\mathbb{C})$ which is positive under partial transposition, i.e., $\rho^\Gamma \geq 0$. As ...
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### How to prove the following bosonic entanglement expression?

Based on the article given by J. L. Ball, I. Fuentes-Schuller, and F. P. Schuller, Phys. Lett. A 359, 550 (2006) had used the following expression of von-Neumann entropy \begin{equation} S = - \...
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### How are witness operators physically implemented?

Let's take an example of an entanglement witness of the form $W = | \phi \rangle \langle \phi | ^{T_2}$ where $| \phi \rangle$ is some pure entangled state. If I wanted to test some state $\rho$, I ...
I have a set of $16 \times 16$ two-qudit density matrices. I would like to study the bound-entanglement for this set, making use of entanglement witnesses for which explicit matrix representations are ...
One can make an entanglement witness by taking the partial transpose of any pure entangled state. Consider $|\phi \rangle$ as any pure entangled state. Then \$W = | \phi \rangle \langle \phi |^{T_2} ...