Quantum Discord

D(A:B) = I(A:B) − J(A:B) — quantum beyond entanglement

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Mutual Info I(A:B)

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Entanglement E(ρ)

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Discord D(A:B)

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Classical J(A:B)

State type

Param p: 0.60

Noise ε: 0.10

Discord = total correlations − classical correlations; non-zero for many separable states.
Werner states: entangled for p>1/3, discord non-zero for p>0.
Discord captures all quantum correlations — resource for quantum computation without entanglement.