Two-qubit states: separable but quantum-correlated states have nonzero discord
Werner State ρ(p)
Concurrence (entanglement): 0.00
Quantum Discord: 0.00
Mutual Information I(A:B): 0.00
Classical Correlation: 0.00
Quantum Discord D(A|B) = I(A:B) − J(A:B) captures quantum correlations beyond entanglement. Separable states (Concurrence=0) can have D>0.
D = S(B) − S(AB) + min_Π S(A|Π_B)
Werner state: entangled iff p > 1/3. Discord nonzero for p > 0.