We investigate the separability of quantum states based on covariance matrices. Separability criteria are presented for multipartite states. The lower bound of concurrence proposed in Phys. Rev. A. 75, 052320 (2007) is improved by optimizing the local orthonormal observables.
@article{arxiv.0805.1632,
title = {Separability and Entanglement of Quantum States Based on Covariance Matrices},
author = {Ming Li and Shao-Ming Fei and Zhi-Xi Wang},
journal= {arXiv preprint arXiv:0805.1632},
year = {2009}
}