Quantum Correlations
Von Neumann entropy S(ρ):-
Entanglement E (concurrence):-
Mutual information I(A:B):-
Quantum discord D(A|B):-
Classical corr J(A|B):-
PPT criterion:-
Discord (Ollivier-Zurek 2001):
D = I(A:B) − J(A|B)
Zero only for fully classical states. Discord > 0 even for separable states.
Hierarchy: I(A:B) ≥ E ≥ 0
Discord can exceed entanglement in mixed states.