Product vectors in the ranges of multi-partite states with positive   partial transposes and permanents of matrices
  In this paper, we consider a system of homogeneous algebraic equations in complex variables and their conjugates, which arise naturally from the range criterion for separability of PPT states. We examine systematically these equations to get sufficient conditions for the existence of nontrivial solutions. This gives us possible upper bounds of ranks of PPT entangled edge states and their partial transposes. We will focus on the multi-partite cases which are much more delicate than the bi-partite cases. We use the notion of permanents of matrices as well as techniques from algebraic geometry through the discussion. 
Young-Hoon Kiem, Seung-Hyeok Kye and Joohan Na
quant-ph math-ph math.MP