Two-qubit Werner states, corresponding to d = 2 above, can be written explicitly in matrix form as W A B ( p , 2 ) = p 6 ( 2 0 0 0 0 1 1 0 0 1 1 0 0 0 0 2 ) + ( 1 − − p ) 2 ( 0 0 0 0 0 1 − − 1 0 0 − − 1 1 0 0 0 0 0 ) = ( p 3 0 0 0 0 3 − − 2 p 6 − − 3 + 4 p 6 0 0 − − 3 + 4 p 6 3 − − 2 p 6 0 0 0 0 p 3 ) . Equivalently, these can be written as a convex combination of the totally mixed state with (the projection onto) a Bell state: W A B ( λ λ , 2 ) = λ λ | Ψ Ψ − − ⟩ ⟩ ⟨ ⟨ Ψ Ψ − − | + 1 − − λ λ 4 I A B , | Ψ Ψ − − ⟩ ⟩ ≡ ≡ 1 2 ( | 01 ⟩ ⟩ − − | 10 ⟩ ⟩ ) , where λ λ ∈ ∈ [ − − 1 / 3 , 1 ] (or, confining oneself to positive values, λ λ ∈ ∈ [ 0 , 1 ] ) is related to p by λ λ = ( 3 − − 4 p ) / 3 . Then, two-qubit Werner states are separable for λ λ ≤ ≤ 1 / 3 and entangled for λ λ > 1 / 3 .