%0 Journal Article
%T Separability and entanglement in 2xN composite quantum systems
%A M. Lewenstein
%A J. I. Cirac
%A S. Karnas
%J Physics
%D 1999
%I arXiv
%X We show that all density operators of 2$\times N$--dimensional quantum systems that remain invariant after partial transposition with respect to the first system are separable. Based on this criterion, we derive a sufficient separability condition for general density operators in such quantum systems. We also give a simple proof of the separability criterion in $2\times 2$--dimensional systems [A. Peres, Phys. Rev. Lett {\bf 77}, 1413 (1996)]
%U http://arxiv.org/abs/quant-ph/9903012v1