Quantifying entanglement of a two-qubit system via measurable and invariant moments of its partially transposed density matrix

@article{Bartkiewicz2015QuantifyingEO,
  title={Quantifying entanglement of a two-qubit system via measurable and invariant moments of its partially transposed density matrix},
  author={Karol Bartkiewicz and Jivr'i Beran and Karel Lemr and Michal Norek and Adam Miranowicz},
  journal={Physical Review A},
  year={2015},
  volume={91},
  pages={022323}
}
We describe a direct method to determine the negativity of an arbitrary two-qubit state in experiments. The method is derived by analyzing the relation between the purity, negativity, and a universal entanglement witness for two-qubit entanglement. We show how the negativity of a two-qubit state can be calculated from just three experimentally accessible moments of the partially transposed density matrix of a two-photon state. Moreover, we show that the negativity can be given as a function of… 

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