Entropy and entanglement bounds for reduced density matrices of   fermionic states
  Unlike bosons, fermions always have a non-trivial entanglement. Intuitively, Slater determinantal states should be the least entangled states. To make this intuition precise we investigate entropy and entanglement of fermionic states and prove some extremal and near extremal properties of reduced density matrices of Slater determinantal states. 
Eric A. Carlen, Elliott H. Lieb, Robin Reuvers
math.OA quant-ph