Separability of rank two quantum states on multiple quantum spaces
  Explicit sufficient and necessary conditions for separability of $N$-dimensional rank two multiparty quantum mixed states are presented. A nonseparability inequality is also given, for the case where one of the eigenvectors corresponding to nonzero eigenvalues of the density matrix is maximally entangled. 
Shao-Ming Fei, Xiu-Hong Gao, Xiao-Hong Wang, Zhi-Xi Wang and Ke Wu