Figure 1

Determination of Gram matrix via conditional overlapping in the case of two polarization-entangled photon pairs. Each source produces a pair of photons in a general mixed-polarization state ${\rho }_{AB}$. The statistics of pairs of clicks is collected on the left-hand side after two elements are measured. On the right side the H-O-M interference is performed. The square of the Gram matrix element equals the probability of the pair of clicks multiplied by that of the double click on the right. The extra boxes with the primed arguments of the rotations $R({\theta }^{\prime },{\varphi }^{\prime })$ represent the measurements in a basis complementary to the original basis associated with the rotations $R(\theta ,\varphi )$ (see main text). The Hermitian conjugate at the rotations correspond to the dualism of Schrödinger and Heisenberg pictures.Reuse & Permissions

Figure 2

Separability of the generalized Werner state of two qubits. Below the red dashed line (representing ${\alpha }_T$) this state is separable. Above the green line (representing ${\alpha }_C$) our criteria (22) based on the mixed-state collectibility detect its entanglement.Reuse & Permissions