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A Werner state〔 〕 is a -dimensional bipartite quantum state density matrix that is invariant under all unitary operators of the form . That is, it is a quantum state ''ρ'' that satisfies : for all unitary operators ''U'' acting on ''d''-dimensional Hilbert space. Every Werner state is a mixture of projectors onto the symmetric and antisymmetric subspaces, with the relative weight ''p''sym being the only parameter that defines the state. : where : are the projectors and : is the permutation operator that exchanges the two subsystems. Werner states are separable for ''p''sym ≥ and entangled for ''p''sym < . All entangled Werner states violate the PPT separability criterion, but for ''d'' ≥ 3 no Werner states violate the weaker reduction criterion. Werner states can be parametrized in different ways. One way of writing them is : where the new parameter ''α'' varies between −1 and 1 and relates to ''p''sym as : == Multipartite Werner states == Werner states can be generalized to the multipartite case.〔Eggeling ''et al.'' (2008)〕 An ''N''-party Werner state is a state that is invariant under for any unitary ''U'' on a single subsystem. The Werner state is no longer described by a single parameter, but by ''N''! − 1 parameters, and is a linear combination of the ''N''! different permutations on ''N'' systems. 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「Werner state」の詳細全文を読む スポンサード リンク
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