Multipartite Entanglement of a Two-Separable State
Stefan Gerke, Jan Sperling, W. Vogel, Yin Cai, Jonathan Roslund, Nicolas Treps, Claude Fabre · Physical Review Letters · 2016
We consider a six-partite, continuous-variable quantum state that we have effectively generated by the parametric down-conversion of a femtosecond frequency comb. We show that, though this state is two-separable, i.e., it does not exhibit "genuine entanglement," it is undoubtedly multipartite entangled. The consideration of not only the entanglement of individual mode decompositions, but also of combinations of those, solves the puzzle and exemplifies the importance of studying different categories of multipartite entanglement.