Critical points of the linear entropy for pure L-qubit states

Abstract

We present a substancially improved version of the method proposed in Sawicki et al (2012, 2014) for finding critical points of the linear entropy for L-qubit system. The new approach is based on the corespondance between momentum maps for abelian and non-abelian groups, as described in Kirwan (1984). The proposed method can be implemented numerically much easier than the previous one.