Canonical Form and Separability of PPT States on Multiple Quantum Spaces
  By using the "subtracting projectors" method in proving the separability of PPT states on multiple quantum spaces, we derive a canonical form of PPT states in ${\Cb}^{K_1} \otimes {\Cb}^{K_2} \otimes ... \otimes {\Cb}^{K_m} \otimes {\Cb}^N$ composite quantum systems with rank $N$, from which a sufficient separability condition for these states is presented. 
Xiao-Hong Wang and Shao-Ming Fei