Constraints on the mixing of states on bipartite quantum systems
  We give necessary conditions for the mixing problem in bipartite case, which are independent of eigenvalues and based on algebraic-geometric invariants of the bipartite states. One implication of our results is that for some special bipartite mixed states, only special mixed states in a measure zero set can be used to mix to get them. The results indicate for many physical problems on composite quantum systems the description based on majorization of eigenvalues is not sufficient 
Hao Chen