Matrix Tensor Product Approach to the Equivalence of Multipartite States   under Local Unitary Transformations
  The equivalence of multipartite quantum mixed states under local unitary transformations is studied. A criterion for the equivalence of non-degenerate mixed multipartite quantum states under local unitary transformations is presented. 
X.H. Gao, S. Alberverio, S.M. Fei, Z.X. Wang