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In the case of systems composed of subsystems the classification of entangled states is richer than in the bipartite case. Indeed, in multipartite entanglement apart from fully separable states and fully entangled states, there also exists the notion of partially separable states.〔 (【引用サイトリンク】title=Multipartite entanglement )〕 == Full and partial separability == The definitions of fully separable and fully entangled multipartite states naturally generalizes that of separable and entangled states in the bipartite case, as follows.〔 Definition (-partite separability (-separability) of systems ): The state of subsystems with Hilbert space is fully separable if and only if it can be written in the form : Correspondingly, the state is fully entangled if it cannot be written in the above form. As in the bipartite case, the set of -separable states is ''convex'' and ''closed'' with respect to trace norm, and separability is preserved under -separable operations which are a straightforward generalization of the bipartite ones: :〔 As mentioned above, though, in the multipartite setting we also have different notions of partial separability.〔 Definition (with respect to partitions ): The state of subsystems is separable with respect to a given partition , where are disjoint subsets of the indices , if and only if it can be written :〔 Definition (): The state is semiseparable if and only if it is separable under all - partitions, .〔 Definition (entanglement ): An -particle system can have at most -particle entanglement if it is a mixture of all states such that each of them is separable with respect to some partition , where all sets of indices have cardinality .〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「multipartite entanglement」の詳細全文を読む スポンサード リンク
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