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Characterization of four-qubit states via Bell inequalities
Hui Zhao, Xing-Hua Zhang, Shao-Ming Fei and Zhi-Xi Wang
A set of Bell inequalities classifying the quantum entanglement of four-qubit states is presented. These inequalities involve only two measurement settings per observer and can characterize fully separable, bi-separable and tri-separable quantum states. In addition, a quadratic inequality of the Bell operators for four-qubit systems is derived.