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Spin squeezing criterion with local unitary invariance

A. R. Usha Devi·Xiaoguang Wang·Barry C Sanders
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Abstract

We propose a new spin squeezing criterion for arbitrary multi-qubit states that is invariant under local unitary operations. We find that, for arbitrary pure two-qubit states, spin squeezing is equivalent to entanglement, and multi-qubit states are entangled if this new spin squeezing parameter is less than 1.

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A. R. Usha Devi, Xiaoguang Wang, Barry C Sanders. 2003-06-30. Spin squeezing criterion with local unitary invariance. https://doi.org/10.1023/b%3Aqinp.0000004125.12489.f4

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