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Nonlinear Improvement of Qubit-qudit Entanglement Witnesses
Shu-Qian Shen, Jin-Min Liang, Ming Li, Juan Yu and Shao-Ming Fei
The entanglement witness is an important and experimentally applicable tool for entanglement detection. In this paper, we provide a strictly nonlinear improvement of any entanglement witness for $2\otimes d$ quantum systems. Compared with any existing entanglement witness, the improved separability criterion only needs two more measurements on local observables. Detailed examples are employed to illustrate the efficiency of the nonlinear improvement for general, optimal and non-decomposable entanglement witnesses.