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     

双模最小关联混合态作为量子信道实现量子隐形传态的保真度

基于Braunstein和Kimble提出的B-K方案以双模最小关联混合态作为量子信道实施对未知量子态的隐形传送，并以传送相干态为例进行了研究.结果表明：双模最小关联混合态作为一种广义的Einstein-Podolsky-Rosen型纠缠态在实现量子隐形传态中能很好地担当量子信道的角色，在纠缠度和压缩度选择适当的条件下被传送未知量子态的保真度可以达到1.这是比双模压缩真空态更优越的量子信道. 关键词： 量子隐形传态 双模最小关联混合态 保真度     

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.     

隐形传送单模压缩态保真度的优化

基于Braunstein与Kimble的连续变量量子隐形传态方案，通过调节输出端位移因子可以优化单模压缩相干态和单模压缩真空态量子隐形传态的保真度；分析了单模压缩态的压缩参数对保真度的影响。     

隐形传送单光子数态保真度的优化

基于Braunstein与Kimble的连续变量量子隐形传态方案,利用双模压缩真空态作为纠缠通道,通过调节输出端位移因子可以优化单光子数态量子隐形传态的保真度。     

单模压缩真空态的量子隐性传态及其保真度的研究

文章基于Braustain和Kimble方案以双模最小关联混态作为量子信道实施对单模压缩真空态的量子隐性传态.研究发现,以混态纠缠态作为量子通道实行量子隐性传态得到输出量子态保真度较小.但是通过利用调解输出端位移因子的保真度的优化方案,我们发现可以在一定的参数范围内可以实现对具有压缩效应的量子态的高保真传送,在一定条件下甚至可以实现保真度为1的量子态的隐性传递.     

关于单模最小关联混态的量子隐性传态及其保真度的研究

基于Braunstein和Kimble方案以双模压缩真空态作为量子信道实施对单模最小关联混态量子隐性传态的可行性进行了研究.我们发现,单模最小关联混态在一定参数范围内呈现出压缩效应这种非经典性质,利用双模压缩真空态作为量子通道可以高保真的传递没有压缩效应的单模最小关联混态,但对呈现压缩效应的单模最小关联混态进行量子隐性传送时得到输出态的保真度较低.而且发现通过调节输出端位移因子的方法不能实现对单模最小关联混态保真度的优化.     

用一个纠缠态实现多粒子纠缠态的量子隐形传送

提出分别在二维和高维系统中利用一个纠缠态作量子通道实现M粒子纠缠态的量子隐形传送方案. 该方案有多个接收者,通过控制引进辅助粒子数,可以任意调节传送后的纠缠态在各接收者之间的粒子数分布, 且成功传送的概率为1. 关键词： 量子隐形传态 纠缠态 量子通道     

利用双模压缩真空态实现量子态的远程传输

借助于双模压缩真空态在EPR纠缠态表象中的表示，研究了用双模压缩真空态作为量子通道 实现任意的单模和双模量子态的远程传输. 关键词： 量子隐形传态 EPR纠缠态 压缩真空态     

囚禁离子非线性J-C模型量子态保真度

用全量子理论研究驻波激光场与囚禁离子相互作用系统中量子态保真度,详细讨论离子质心在驻波激光场中位置及离子初始状态对保真度的影响.结果表明:随着囚禁离子从远离驻波激光场波节处向波节处移动,量子态保真度振荡频率越来越高,振荡幅度几乎不变,且保真度到达第一个极小值所用时间越来越短,但不会出现信息完全失真;随着囚禁离子处于基态概率增加,量子态保真度振荡频率几乎不变,振荡幅度越来越小,也不会出现信息完全失真;在信息储存或传递过程中,囚禁离子量子态失真比系统和驻波场量子态失真小.     

Fidelity between Gaussian mixed states with quantum state quadrature variances

In this paper, from the original definition of fidelity in a pure state, we first give a well-defined expansion fidelity between two Gaussian mixed states. It is related to the variances of output and input states in quantum information processing. It is convenient to quantify the quantum teleportation(quantum clone) experiment since the variances of the input(output) state are measurable. Furthermore, we also give a conclusion that the fidelity of a pure input state is smaller than the fidelity of a mixed input state in the same quantum information processing.     

弱测量对四个量子比特量子态的保护

廖湘萍等(Chin.Phys.B 23 020304,2014)指出弱测量和弱测量反转操作可以保护三个量子比特的纠缠,提高保真度.本文将弱测量方法推广至四个量子比特的情况,研究了几种典型四个量子比特量子态的演化.结果表明:在振幅阻尼通道中,弱测量方法能够有效地提高系统量子态的保真度.分析了影响量子态保真度的各种因素,对比了不同量子态的演化特征,划分了量子态保真度提高的敏感区域.最后,对弱测量方法抑制量子态衰减的内在机制做了合理的物理解释.     

Controlled Implementation of Non-local CNOT Operation Using Three-Qubit Entanglement

We investigate the controlled implementation of a non-local CNOT operation using a three-qubit entangled state. Firstly, we show how the non-local CNOT operation can be implemented with unit fidelity and unit probability by using a maximally entangled GHZ state as controlled quantum channel. Then, we put forward two schemes for conclusively implementing the non-local operation with unit fidelity by employing a partially entangled pure GHZ state as quantum channel. The feature of these schemes is that a third side is included, who may participate the process of quantum non-local implementation as a supervisor. Furthermore, when the quantum channel is partially entangled, the third one can rectify the state distorted by imperfect quantum channel. In addition to the GHZ class state, the W class state can also be used to implement the same non-local operation probabilistically. The probability of successful implementation using the W class state is always less than that using the GHZ class state.     

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。     

基于电磁诱导透明机制的压缩光场量子存储

光场的量子存储不仅是构建量子计算机的重要基础,而且是实现量子中继和远距离量子通信的核心部分.由于存在不可避免的光学损耗,光学参量放大器产生的压缩真空态光场将变为压缩热态光场,不再是最小不确定态.因此,压缩热态光场的量子存储是实现量子互联网的关键.在原子系综中利用电磁诱导透明机制能够实现量子态在光场正交分量和原子自旋波之间的相互映射,即受控量子存储.本文根据量子存储的保真度边界,研究了实现压缩热态光场量子存储的条件.量子存储的保真度边界是通过经典手段能够达到的最大保真度,当保真度大于该边界时,就实现了量子存储.通过数值计算分析了不同情况下压缩热态光场的量子存储保真度边界,以及存储保真度随存储效率的变化关系,得到了实现量子存储的条件,为连续变量量子存储实验设计提供了直接参考.     

Entanglement fidelity of the standard quantum teleportation channel

We consider the standard quantum teleportation protocol where a general bipartite state is used as entanglement resource. We use the entanglement fidelity to describe how well the standard quantum teleportation channel transmits quantum entanglement and give a simple expression for the entanglement fidelity when it is averaged on all input states.     

Applications of quantum cloning

Quantum Cloning Machines (QCMs) allow for the copying of information, within the limits imposed by quantum mechanics. These devices are particularly interesting in the high-gain regime, i.e., when one input qubit generates a state of many output qubits. In this regime, they allow for the study of certain aspects of the quantum to classical transition. The understanding of these aspects is the root of the two recent applications that we will review in this paper: the first one is the Quantum Cloning Radiometer, a device which is able to produce an absolute measure of spectral radiance. This device exploits the fact that in the quantum regime information can be copied with only finite fidelity, whereas when a state becomes macroscopic, this fidelity gradually increases to 1. Measuring the fidelity of the cloning operation then allows to precisely determine the absolute spectral radiance of the input optical source. We will then discuss whether a Quantum Cloning Machine could be used to produce a state visible by the naked human eye, and the possibility of a Bell Experiment with humans playing the role of detectors.     

Realistic teleportation of coherent states using squeezed vacuum states

This paper presents a realistic scheme for the teleportation of coherent states in which a two-mode squeezed vacuum state serves as the quantum channel and the position-sum and momentum-difference of two local modes serve as the measuring observables. The average fidelity of the teleportation of coherent states is derived for finite squeezing parameters and it turns out that fidelity greater than 1/2 cannot be achieved by using a classical channel alone and the probability distribution of the measurement result is a Gaussian distribution around the unknown parameter of the input coherent state with a width given by the squeezing parameter.     

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.