噪声环境下基于两体纠缠态的远程态制备

本文研究了量子噪声对分别以Einstein-Podolsky-Rosen （EPR）态和两体部分纠缠态作为量子信道来远程制备单比特态的量子过程的影响. 通过求解Lindblad形式的主方程,得到量子信道随时间的演化,采用迹距离来度量不同噪声情况下输出态与初态的接近程度. 研究表明,作用在z方向的噪声对远程态制备的影响最弱,而同时作用在x,y,z方向的噪声对远程态制备的影响最强. 关键词： 远程态制备 迹距离 纠缠态 噪声信道     

利用纠缠交换在理想和非理想条件下的远程态制备(英文)

提出了利用纠缠交换技术实现一个纠缠态的远程制备.考虑在量子信道没有遭受噪声影响的条件下,利用一对两粒子纠缠态作为量子信道去实现远程态制备.此外我们考察了噪声存在时的远程态的制备,研究显示不同类型的量子噪声对远程态制备过程的保真度的影响不同.对一个确定量子态,我们考察了消相干效应对其远程制备的影响.     

一种低经典通信消耗的量子远程态制备方案

设计了一组新的量子远程态制备步骤,在发送方对手中的粒子完成测量后,接收方采用该步骤可以有效降低远程态制备的经典通信消耗-给出一种利用部分纠缠的三粒子Greenberger-Horne-Zeilinger(GHZ)态和部分纠缠的二粒子态作信道,远程制备一个三粒子GHZ态的方案,以此方案为例具体说明上述方法的运用步骤并给出了该方法的适用范围-结果表明,运用该方法后只需消耗1bit经典信息即可远程制备一个三粒子GHZ态- 关键词： 远程态制备 经典通信消耗 三粒子Greenberger-Horne-Zeilinger态 量子信道     

利用单个三粒子最大GHZ态或两个EPR态隐形传送任意三粒子GHZ态

提出利用单个三粒子最大Greenberger-Horne-Zeilinger (GHZ)态或两个Einstein-Podolsky-Rosen (EPR)态作为量子信道确定性隐形传送任意三粒子GHZ态的两个方案，并将方案推广至隐形传送任意n(n≥4)粒子GHZ态的情况.讨论了量子信道受噪声影响时隐形传态的保真度.研究发现，当作为量子信道的单个三粒子最大GHZ态受到噪声影响时，隐形传态的保真度仅与量子信道的纠缠度有关，而当作为量子信道的两个EPR态受到噪声影响时，隐形传态的保真度不仅与量子信道的纠缠度有关，还与待传送态的纠缠度有关.所提出的方案具有节省量子信道纠缠资源的特点. 关键词： 隐形传态 三粒子Greenberger-Horne-Zeilinger态 量子逻辑门 保真度     

用三粒子纠缠态作量子信道远程操纵单比特旋转

提出用三粒子纠缠态作量子信道远程操纵单比特旋转的理论方案。首先，我们利用最大纠缠的GHZ态的性质远程操纵单比特旋转，其保真度和成功几率均为1。 我们还提出了两个用部分纠缠的GHZ态作量子信道实现保真度为1的远程操纵单比特旋转的方案。这些方案的特点是，两地之间还存在一第三者，他作为监控方参与量子远程操纵过程，特别地，当量子信道为部分纠缠态时，他能矫正被非理想量子信道致畸的量子态。除了GHZ型态外，我们还证明了W型态亦可用作量子信道远程操纵单比特旋转，但后者的成功几率总是小于前者。     

利用广义Bell态信道联合远程制备一个任意三量子比特态

研究了一个联合远程制备任意三量子比特态的方案。该方案利用广义的Bell态作为量子信道,两个发送者分别选择合适的测量基进行测量,然后利用经典信道把测量结果传送出去,接收者根据测量结果对自己手中的粒子采取适当的幺正操作,然后引入辅助粒子并进行选择性测量,就能概率性的得到想要制备的量子态。研究结果表明:利用不同形式的广义Bell态信道成功实现联合远程制备一个任意三量子比特态的概率是一样的,当量子信道处于最大纠缠态时,可以得到最大的成功概率。     

利用两个纠缠对隐形传送三原子W态

提出利用两个Einstein-Podolsky-Rosen(EPR)态作为量子信道隐形传送任意三原子W态的方案,并将该方案推广至隐形传送任意N（N 4）原子W态. 研究了实施方案的两种方法,给出了完成隐形传态的一种新思路：解纠缠—隐形传送—重构纠缠.讨论了量子信道受噪声影响时隐形传态的保真度. 结果表明,当作为量子信道的两个最大纠缠态受到噪声影响时,隐形传态的保真度不仅与量子信道的纠缠度有关,还与待传送态中某一子系统的共生纠缠度有关. 所提出的方案具有操作简便,节省量子信道纠缠资源的特点.     

利用两个纠缠对隐形传送任意三原子W态

提出利用两个Einstein-Podolsky-Rosen(EPR)态作为量子信道隐形传送任意三原子W态的方案,并将该方案推广至隐形传送任意N(N≥4)原子W态.研究了实施方案的两种方法,给出了完成隐形传态的一种新思路:解纠缠-隐形传送-重构纠缠.讨论了量子信道受噪声影响时隐形传态的保真度.结果表明,当作为量子信道的两个最大纠缠态受到噪声影响时,隐形传态的保真度不仅与量子信道的纠缠度有关,还与待传送态中某一子系统的共生纠缠度有关.所提出的方案具有操作简便,节省量子信道纠缠资源的特点.     

量子纠缠态的普适远程克隆

提出一种任意两粒子纠缠态1→2普适远程克隆方案. 此方案仅需一个特殊的四粒子纠缠态作为量子信道, 就可使处于空间不同位置的两个接收者分别以5/6的保真度得到任意输入态的近似拷贝, 该保真度远高于已有方案中的保真度. 将方案推广到任意两粒子纠缠态1→N(N>2)普适远程克隆的情况, 可使处于不同地点的N个接收者分别以(2N+1)/(3N)的保真度得到输入态的近似拷贝. 另外, 提出一种以上述单个特殊四粒子纠缠态作为量子信道, 在多目标量子比特受控非门和 关键词： 量子纠缠态 普适远程克隆 保真度     

连续变量Einstein-Podolsky-Rosen纠缠态光场在光纤信道中分发时纠缠的鲁棒性

Einstein-Podolsky-Rosen纠缠态光场是实现基于光纤的连续变量量子信息处理的重要量子光源,其在光纤信道分发时会与信道相互作用发生解纠缠,影响量子信息处理的性能.本文利用部分转置正定判据分析了Einstein-Podolsky-Rosen纠缠态光场在单通道和双通道光纤信道分发方案中,其初始态的关联正交分量对称性、模式对称性、纯度和光纤信道额外噪声对传输距离、纠缠态光场的纠缠特性及鲁棒性的影响.在单通道和双通道方案中,光纤信道的额外噪声都会引起纠缠态光场的解纠缠,随着噪声的增大,传输距离迅速减小.要保持Einstein-Podolsky-Rosen纠缠态光场在光纤损耗信道中的纠缠鲁棒性,双通道方案比单通道方案对初始态的关联正交分量对称性和纯度方面的要求更为苛刻.而且单光纤噪声通道分发方案对模式对称性参数不敏感,模式对称性参数变化不会引起解纠缠,也不影响最大传输距离和纠缠鲁棒性特征;在双光纤噪声通道分发时,模式不对称参数降低会减小最大传输距离,并出现纠缠突然死亡.     

Trace Distance of Remote State Preparation Through Noisy Channels

In this paper, we study remote state preparation (RSP) by w state through noisy channels. The trace distance is used to describe how close the original state is to the output state. Studies show the trace distance is a function of decohenrence rates and angles of the state to be prepared. At the same time, we investigate the influence of different types of noises on the trace distance and find the various types of noises have different degrees of influence on the trace distance for a definite qubit. We also study changes of the trace distance against polar and azimuthal angles.     

Remote Preparation of an Entangled State in Nonideal Conditions

In this paper, the theoretical investigation of remote preparation of an entangledstate is studied in nonideal conditions. Our studies include two parts. In the first part, we consider the remote state preparation （RSP） of an entangled state through two equally noisy quantum channel states, namely, a mixture of Bell states. Studies show there is a particular mixed-state channel for which all pure entangled states remain entangled after this inexact RSP. In the second part, we suppose that noises which quantum channels suffer from can be expressed as the Lindblad operators. The master equation of the system can be expressed in the Lindblad form. Through solving the master equation, we calculate the fidelity as a function of decoherence rates and parameters of the state to be prepared. For a given entangled state, we investigate the influence of different types of noises on the fidelity.     

Remote Preparation of an Entangled State in Nonideal Conditions

In this paper, the theoretical investigation of remote preparation of an entangled state is studied in nonideal conditions. Our studies include two parts. In the first part, we consider the remote state preparation (RSP) of an entangled state through two equally noisy quantum channel states, namely, a mixture of Bell states. Studies show there is a particular mixed-state channel for which all pure entangled states remain entangled after this inexact RSP. In the second part, we suppose that noises which quantum channels suffer from can be expressed as the Lindblad operators.The master equation of the system can be expressed in the Lindblad form. Through solving the master equation, we calculate the fidelity as a function of decoherence rates and parameters of the state to be prepared. For a given entangled state, we investigate the influenceof different types of noises on the fidelity.     

High efficient scheme for remote state preparation with cavity QED

In this paper, a scheme is proposed for remote state preparation （RSP） with cavity quantum electrodynamics （QED）. In our scheme, two observers share two-atom nonmaximally entangled state as quantum channels and can realize remote preparation of state of an atom. We also propose a generalization for remote preparation of N-atom entangled state by （N＋1）-atom GHZ-like state （N ≥ 2）. By this scheme, one single-atom projective measurement is enough for the RSP of a qubit or N-atom entangled state, and the probability of success for RSP is unity. Furthermore, we have considered the case where observers use W-like state as quantum channels to realize RSP of a qubit. We compare our scheme with existing ones.     

Non-Markovian effect on remote state preparation

Memory effect of non-Markovian dynamics in open quantum systems is often believed to be beneficial for quantum information processing. In this work, we employ an experimentally controllable two-photon open system, with one photon experiencing a dephasing environment and the other being free from noise, to show that non-Markovian effect may also have a negative impact on quantum tasks such as remote state preparation: For a certain period of controlled time interval, stronger non-Markovian effect yields lower fidelity of remote state preparation, as opposed to the common wisdom that more information leads to better performance. As a comparison, a positive non-Markovian effect on the RSP fidelity with another typical non-Markovian noise is analyzed. Consequently, the observed dual character of non-Markovian effect will be of great importance in the field of open systems engineering.     

在四能级系统中实现单粒子及两粒子量子态的远程制备

本文提出两种协议来实现远程态制备.第一个方案描述基于两体最大纠缠信道,如何远程制备四能级系统中的任意单粒子量子态.然后由第一个方案概括出第二个方案,即在四能级系统中实现两粒子纠缠态的远程制备方案.在两种制备的过程中, 需要分别实施一个单粒子投影测量和一个两粒子投影测量.结果表明,两个方案都能以大于25%的几率忠信地实现.此外,对于两类特殊态,即赤道态和实数态,其成功概率大大提高至100%,此时我们几率的协议转变为决定性的协议.     

在四能级系统中实现单粒子及两粒子量子态的远程制备

本文提出两种协议来实现远程态制备.第一个方案描述基于两体最大纠缠信道,如何远程制备四能级系统中的任意单粒子量子态.然后由第一个方案概括出第二个方案,即在四能级系统中实现两粒子纠缠态的远程制备方案.在两种制备的过程中, 需要分别实施一个单粒子投影测量和一个两粒子投影测量.结果表明,两个方案都能以大于25%的几率忠信地实现.此外,对于两类特殊态,即赤道态和实数态,其成功概率大大提高至100%,此时我们几率的协议转变为决定性的协议.     

Remote state preparation of a photonic quantum state via quantum teleportation

We demonstrate an experimental realization of remote state preparation via the quantum teleportation algorithm, using an entangled photon pair in the polarization degree of freedom as the quantum resource. The input state is encoded on the path of one of the photons from the pair. The improved experimental scheme allows us to control the preparation and teleportation of a state over the entire Bloch sphere with a resolution of the degree of mixture given by the coherence length of the photon pair. Both the preparation of the input state and the implementation of the quantum gates are performed in a pair of chained displaced Sagnac interferometers, which contribute to the overall robustness of the setup. An average fidelity above 0.9 is obtained for the remote state preparation process. This scheme allows for a prepared state to be transmitted on every repetition of the experiment, thus giving an intrinsic success probability of 1.     

Deterministic joint remote preparation of an arbitrary two-qubit state in the presence of noise

Using two tripartite Greenberger-Horne-Zeilinger （GHZ） states as the shared channels, we investigate the noise effects on the deterministic joint remote preparation of an arbitrary two-qubit state. By unitary matrix decomposition procedure, we first construct the quantum logic circuit of the deterministic joint remote state preparation protocol. Then, we analytically derive the fidelity and the average fidelity for the deterministic joint remote preparation of an arbitrary two- qubit state and of four types of special two-qubit states under the influence of the Pauli noises. It is found that the fidelity depends on the noise types, the qubit-environment coupling strength, and the state to be remotely prepared. Moreover, even if the two GHZ channels are subject to the same environmental noises, the average fidelities for remotely preparing different two-qubit states display different time evolution behaviors. The remote preparation of the identical two-qubit states also shows that the average fidelities affected by different noisy environments exhibit different evolution actions.