Four-tangle for pure states
S. Shelly Sharma, Naresh Kumar Sharma · Physical Review A · 2010
A novel approach to construct invariants that detect entanglement is presented. The method is based on the Peres separability criterion and Sylvester's criterion. An expression for four-tangle is obtained by examining the negativity fonts present in a four-way partial transpose under local unitary operations. An alternative derivation of three-tangle is also given.