Generation of six-partite continuous-variable entanglement using a nonlinear photonic crystal by frequency conversions

We theoretically show that six-partite continuous-variable entanglement can be generated by nonlinear optical processes conducted in a designed photonic crystal-like periodically poled lithium niobat (PPLN). The processes consist of a nonlinear parametric down-conversion and four sum-frequency processes. The characteristics of the six-partite entanglement among the six beams are analyzed both above and below the threshold by applying a sufficient inseparability criterion for multipartite continuous-variable entanglement. We investigated our proposal for a specific case of a PPLN optical superlattice with fixed light and material properties.