Mixedness of the N-qubit states with exchange symmetry  

作　　者：胡明亮 惠小强 

机构地区：[1]Department of Applied Mathematics and Applied Physics,Xi’an Institute of Posts and Telecommunications

出　　处：《Chinese Physics B》2008年第10期3559-3564,共6页中国物理B（英文版）

基　　金：Project supported by the National Natural Science Foundation of China (Grant No 10547008);Specialized Research Program of Education Bureau of Shaanxi Province (Grant No 08JK434);the Youth Foundation of Xi’an Institute of Posts and Telecommunications (Grant No ZL2008-11)

摘　　要：The mixedness of the N-qubit quantum states with exchange symmetry has been studied, and the results show that the linear entropy of the single qubit reduced density matrix （RDM）, which can describe the mixedness, is completely determined by the expectation values 〈Sz〉 and 〈S±〉 for both the pure and the mixed states. The mixedness of the pure states can be used to describe the bipartite entanglement, as an example we have calculated the mixedness of the Dicke state and the spin squeezed Kitagawa-Ueda state. For the mixed states, we determine the mixedness properties of both the ground states and the thermal states in mean-field clusters of spin-1/2 particles interacting via the anisotropy Heisenberg XXZ interaction, and found for the ferromagnetic case （J 〈 0）, the mixedness will approximate to the pairwise entanglement when the anisotropic parameter △ 〉 △c.The mixedness of the N-qubit quantum states with exchange symmetry has been studied, and the results show that the linear entropy of the single qubit reduced density matrix （RDM）, which can describe the mixedness, is completely determined by the expectation values 〈Sz〉 and 〈S±〉 for both the pure and the mixed states. The mixedness of the pure states can be used to describe the bipartite entanglement, as an example we have calculated the mixedness of the Dicke state and the spin squeezed Kitagawa-Ueda state. For the mixed states, we determine the mixedness properties of both the ground states and the thermal states in mean-field clusters of spin-1/2 particles interacting via the anisotropy Heisenberg XXZ interaction, and found for the ferromagnetic case （J 〈 0）, the mixedness will approximate to the pairwise entanglement when the anisotropic parameter △ 〉 △c.

关 键 词：mixedness linear entropy symmetric quantum state 

分 类 号：O413.1[理学—理论物理]