All degree six local unitary invariants of k qudits
  We give explicit index-free formulae for all the degree six (and also degree four and two) algebraically independent local unitary invariant polynomials for finite dimensional k-partite pure and mixed quantum states. We carry out this by the use of graph-technical methods, which provides illustrations for this abstract topic. 
Szil\'ard Szalay
quant-ph math-ph math.MP