Entanglement fidelity of channel adaptive quantum codes

We study the performances of quantum channel adaptive [4,1] code transmitting in a joint amplitude damping and dephasing channel, the [6,2] code transmitting in an amplitude damping channel by combining the encoding, noise process, and decoding as one effective channel. We explicitly obtain the entanglement fidelities. The recovery operators of the [6,2] code are given. The performance is nearly optimal compared with that of the optimal method of semidefinite programming.     

The separability of two-mode Gaussian state under amplification and symmetric damping

The performances of a two-mode Gaussian state under parametric amplification, symmetric amplitude damping and thermal noise are studied. The time-dependent complex correlation matrix of the state in evolution is given. The separability of the final two-mode Gaussian state is examined under symmetric amplification and asymmetric amplification separately.     

Perturbation theory of von Neumann entropy

In quantum information theory, von Neumann entropy plays an important role; it is related to quantum channel capacities. Only for a few states can one obtain their entropies. In a continuous variable system, numeric evaluation of entropy is not easy due to infinite dimensions. We develop the perturbation theory for systematically calculating von Neumann entropy of a non-degenerate system as well as a degenerate system.     

单模费米热噪声信道量子容量的估计

从量子信道的算符求和表象出发,对单模费米系统量子信道进行了参数化.参数化的结果得到另一类费米热噪声量子信道.给出了两类费米热噪声量子信道上相干信息的最大值,以估计信道的量子容量. 关键词： 量子容量 相干信息 费米热噪声信道     

多进制量子图态纠缠的确定

图态是可以与数学上的图对应起来的多组分纠缠态,图的顶点在此扮演多进制量子位而连线则表示两个多进制量子位之间的相互作用．图态在量子纠错码、多体量子计算和单向量子计算中起重要作用．本文系统研究多进制图态纠缠,使用迭代计算等方法计算了局域幺正变换和图同构下不等价的所有9点图以下的三进制图态的纠缠及一部分四进制和五进制图态的纠缠,纠缠测度可以是几何纠缠、相对熵纠缠和鲁棒性纠缠．我们对计算结果进行了分类,并分析了所得到的最近分离态．     

Relative Entropy of Entanglement of a Kind of Two-Qubit Entangled States

We strictly prove that some block diagonalizable two-qubit entangled state with six non-zero elements reaches its quantum relative entropy entanglement by a separable state having the same matrix structure. The entangled state comprises local filtering result state as a special case.     

量子热噪声信道在纠缠辅助下的容量

研究了量子纠缠辅助下输入功率受限时的单模热辐射噪声信道传输经典信息的容量问题，和带有放大或衰减的单模热噪声信道的相应问题。对热噪声信道，表明了容量在输入信号为热噪声信号时达到，压缩态无助于达到信道容量CE；对带有放大或衰减的单模热噪声信道，说明了容量同样在输入为热噪声态时达到。     

基于量子相干性的四体贝尔不等式构建

贝尔不等式在定域性和实在性的双重假设下,对于被分隔的粒子同时被测量时其结果的可能关联程度建立了一个严格的限制,违反贝尔不等式确保量子态存在纠缠.本文利用量子相干性的l1和相对熵测度构建了四体量子贝尔不等式,发现一般实系数Greenberger-Horne-Zeilinger纯态和簇纯态总是违反四体相对熵相干性测度贝尔不等式,因此违反四体相对熵相干性测度贝尔不等式的这些态是纠缠态.     

The entanglement of several graph states

We exactly evaluate the entanglement of a six vertex and a nine vertex graph states which correspond to non ??two-colorable?? graphs. to non ??two-colorable?? graphs. The upper bound of entanglement for five vertex ring graph state is improved to 2. is improved to 2.9275, less than the upper bound determined by local operations and classical communication. communication. An upper bound of entanglement is proposed based on the definition of graph state. state.     

量子高斯态的纠缠原因分析

量子纠缠是实现量子计算和量子通信的关键因素,纠缠是量子信息论中的一种资源.量子高斯态是最重要的量子连续变量态,关于量子高斯态的纠缠条件,纠缠度量等已有许多研究.