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Spin squeezing inequalities and entanglement of $N$ qubit states

J. Korbicz·J. I. Cirac·M. Lewenstein
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Abstract

We derive spin squeezing inequalities that generalize the concept of the spin squeezing parameter and provide necessary and sufficient conditions for genuine 2-, or 3- qubit entanglement for symmetric states, and sufficient condition for general states of $N$ qubits. Our inequalities have a clear physical interpretation as entanglement witnesses, can be relatively easy measured, and are given by complex, but {\it elementary} expressions.

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J. Korbicz, J. I. Cirac, M. Lewenstein. 2005-09-14. Spin squeezing inequalities and entanglement of $N$ qubit states. https://doi.org/10.1103/physrevlett.95.120502

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