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Questions tagged [werner-states]

For questions regarding well-known Werner States, which are states that are entangled but are still incapable of violating any Bell nonlocality inequality. This means that those states have an explicit local hidden variable model construction.

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How do two-way protocols allow to extract entanglement from states like Werner's?

As discussed in [Lo and Popescu 1999], it is always possible to distill entanglement from pure bipartite states using a one-way protocol. The gist of the idea, as I understand it, is Proposition 1 in ...
glS's user avatar
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1 vote
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Can we use a Werner state for quantum teleportation? [duplicate]

Some background: The quantum teleportation protocol requires first that Alice and Bob share an entangled state, say a Bell state $|\psi^{+}\rangle_{AB}$. There is another state $|\psi\rangle_{A'}$ to ...
Physkid's user avatar
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10 votes
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Are there separable $\rho$ that cannot be decomposed with less than $\operatorname{rank}(\rho)^2$ pure product states?

In What separable $\rho$ only admit separable pure decompositions with more than $\mathrm{rank}(\rho)$ terms?, examples were given of separable states $\rho$ with separable decompositions requiring ...
glS's user avatar
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4 votes
1 answer
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Is there a way to compute how many hidden variables are needed to describe a given local state?

Consider a bipartite state $\rho$ that is local. By local I mean here that there is a local hidden variable model explaining the correlations resulting from measuring $\rho$. In other words, $\rho$ ...
glS's user avatar
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4 votes
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How to show that Werner states produce correlations explainable via local hidden variable models?

Werner states can be written as $$\rho_W= p\frac{\Pi_+}{\binom{n+1}{2}} +(1-p)\frac{\Pi_-}{\binom{n}{2}}, $$ with $\Pi_\pm\equiv\frac12(I\pm\mathrm{SWAP})$ projectors onto the $\pm1$ eigenspaces of ...
glS's user avatar
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2 votes
1 answer
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How do I represent a Werner state in ket notation?

I want to represent Werner state in the form of ket vector notation. Is there a way in which I can represent it in vector form?
Ganesh M's user avatar
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8 votes
2 answers
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What is a separable decomposition for the Werner state?

Consider the two-qubit Werner state, defined as $$\rho_z = z |\Psi_-\rangle\!\langle \Psi_-| + \frac{1-z}{4}I, \quad |\Psi_-\rangle\equiv\frac{1}{\sqrt2}(|00\rangle-|11\rangle),$$ for $z\ge0$. Using ...
glS's user avatar
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