Error Tolerance in Constructing Cluster States

We consider the problem often encountered in constructing large cluster states, that is, the σx measurements in the depolarizing noise, and present a regulation to calculate the error propagation and the accumulation. Rohde et al. first pointed out the question [Phys. Rev. A 75 （2007） 010302（R）]. A quantitative analysis is given on the disadvantage influence of the probabilistic gate and noisy environment on the construction of two-dimensional （213） scalable cluster states. Positivity of partial transpose criteria is used to predict whether the final state is distillable or not. A critical value on the error tolerance in constructing cluster states is determined, which could be used as a test-bed for successful construction of scalable 2D cluster states. Furthermore, our quantitative analysis would also be helpful to find optimal approach to suppress the noise accumulation.     

制备三量子位和四量子位核磁共振等效纯态

基于时间平均法,给出了在同核系统中制备三量子位和四量子位核磁共振等效纯态的方案.利用Λn(not)门,本文的方案大大减少了制备等效纯态所需的操作次数在三同核系统中制备三量子位核磁共振等效纯态只需三次操作,在四同核系统中制备四量子位核磁共振等效纯态只需五次操作.然后在一个链状耦合的同核系统中实验制备三量子位核磁共振等效纯态,验证了本文的方案;并且给出了四量子位方案的模拟结果谱图.     

量子纯态的纠缠度

纠缠态在量子计算和量子通讯中起着重要作用.考虑了量子纯态在时间反演变换下的行为以及相应的密度矩阵在Hilbert-Schmidt空间中的表示,并由此对纠缠度给出较为直观的几何解释. 关键词：     

A symmetric geometric measure and the dynamics of quantum discord

A symmetric measure of quantum correlation based on the Hilbert-Schmidt distance is presented in this paper. For two-qubit states, we considerably simplify the optimization procedure so that numerical evaluation can be performed efficiently. Analytical expressions for the quantum correlation are attained for some special states. We further investigate the dynamics of quantum correlation of the system qubits in the presence of independent dissipative environments. Several nontrivial aspects are demonstrated. We find that the quantum correlation can increase even if the system state is suffering from dissipative noise. Sudden changes occur, even twice, in the time evolution of quantum correlation. There exists a certain correspondence between the evolution of quantum correlation in the systems and that in the environments, and the quantum correlation in the systems will be transferred into the environments completely and asymptotically.     

关于量子基态的一种解法

通过一个积分变换,量子系统的能量本征值问题可转化为求解非线性的Riccati方程,由它可以容易地求出基态能量及相应的波函数,讨论了此方法与通常的因子化方法的关系并以各种常见的系统作为显示此方法优越性的示范。 关键词：     

Bell Theorem without Inequality for Some Generalized GHZ and W States

Bell＇s theorem without inequalities is applied for some general Greenberger-Horn-Zeilinger （GHZ） states and W states and a wide range of such states can exhibit all-versus-nothing conflict between local realism and quantum theory. The case of standard GHZ state is contained in our proposal. For some generalized GHZ states more intensive violation on local realism is manifested.     

Correlations Existing in Three-Qubit Product States

Analytic results of the relationship between local noncommutativity and non-violations of Svetlichny inequalities for three-qubit separable states are obtained. It is shown that the converse trade-off relations presented by Seevinck and Uffinck [Phys. Rev. A 2007 76 042105] do not always hold for three-qubit states, and that there exists some correlation even though the state is the simple product state.     

制备三量子位和四量子位核磁共振等效纯态

基于时间平均法,给出了在同核系统中制备三量子位和四量子位核磁共振等效纯态的方案.利用Λn(not)门,本文的方案大大减少了制备等效纯态所需的操作次数:在三同核系统中制备三量子位核磁共振等效纯态只需三次操作,在四同核系统中制备四量子位核磁共振等效纯态只需五次操作.然后在一个链状耦合的同核系统中实验制备三量子位核磁共振等效纯态,验证了本文的方案 并且给出了四量子位方案的模拟结果谱图     

混合纠缠态的几何描述

给出了Hilbert-Schmidt(H-S)空间中密度矩阵的向量表示,建立了完整的H-S空间中的度规 ,由此将混合纠缠态的判据纳入到直观的几何图像中,讨论了最大混合态附近可分离态的紧 致邻域,得到了关于该邻域体积测度的更强的结果. 关键词： 纠缠 混合态 Hilbert-Schmidt空间