Combinatorial laplacians and positivity under partial transpose

Roland Hildebrand, Stefano Mancini, Simone Severini

Density matrices of graphs are combinatorial laplacians normalized to have trace one (Braunstein \emph{et al.} \emph{Phys. Rev. A,} \textbf{73}:1, 012320 (2006)). If the vertices o…