单光子纠缠态的纠缠转移和量子隐形传态

使用光学分束器和单光子源，利用单光子态和真空态制备出了纠缠单光子态.利用光学分束器作用和单光子探测，实现了三个通讯伙伴之间的纠缠转移.提出了一个关于纠缠单光子态的量子隐形传态方案.在这个方案中，被传送的是一个未知的单光子纠缠态.通讯双方使用的量子信道是两个单光子纠缠态.通过使用分束器作用和对输出态进行光子测量以及在经典信息的帮助下，纠缠转移和量子隐形传态的过程被完成.     

单光子纠缠态的纠缠浓缩(英文)

通过分析光学分束器对单光子态的作用特点,描述了一个利用单光子态和真空态制备纠缠单光子态的方法;提出了一个实现单光子纠缠态纠缠浓缩的方案。在这个方案中,两个单光子部分纠缠态被用来作为量子信道,通过利用光学分束器作用和单光子探测器探测完成了这个纠缠浓缩的过程。结果表明,对于单光子纠缠态,利用这种方法总有一定的几率可以从部分纠缠纯态中提纯出最大纠缠态。     

Entanglement concentration and teleportation of multipartite entangled states in an ion trap

We propose an effective scheme for the entanglement concentration of a four-particle state via entanglement swapping in an ion trap. Taking the maximally entangled state after concentration as a quantum channel, we can faithfully and determinatively teleport quantum entangled states from Alice to Bob without the joint Bell-state measurement. In the process of constructing the quantum channel, we adopt entanglement swapping to avoid the decrease of entanglement during the distribution of particles. Thus our scheme provides a new prospect for quantum teleportation over a longer distance. Furthermore, the success probability of our scheme is 1.0.     

Teleportation of N-particle entangled W state via entanglement swapping

A scheme for teleporting an unknown N-particle entangled W state is proposed via entanglement swapping. In this scheme, N maximally entangled particle pairs are used as quantum channel. As a special case, the teleportation of an unknown four-particle entangled W state is studied.     

Probabilistic Teleportation of Three-Atom State via Five-Atom Cluster State

A scheme for probabilistic teleportation of an unknown three-atom entangled state via a five-atom non-maximally entangled cluster state as quantum channel is proposed. In this scheme, the sender performs two Bell state and a single-atom measurements on the atoms, the receiver can reconstruct the original state with a certain probability by introducing an auxiliary atom and operating appropriate unitary transformations and controlled-not (C-not) operations according to the sender Alice's measurement results. As a result, the probability of successful teleportation is determined by the smallest two of the coefficients'absolute values of the cluster state. The considerable advantage of our scheme is that we employ a non-maximally entangled cluster state as quantum channel in the scheme, which can greatly reduce the amount of entanglement resources and need less classical bits. If we employ a maximally entangled cluster state as quantum channel, the probabilistic teleportation scheme becomes usual teleportation, the successful probability being 100%.     

单光子纠缠态并发度的直接测量

通过分析光学分束器对单光子态的作用关系,提出了一个利用分束器和光子数探测器的单光子纠缠的直接测量方案.方案中用到单光子与空间模纠缠及其两个备份,并让它们通过一个50:50的分束器.选用并发度为纠缠度量,其可由单光子探测器的探测概率直接获得.此方案不需复杂的量子态层析方法,同时只用到在量子信息处理中常用的光学器件,增强了方案在实验上实现的可行性.     

电子自旋辅助实现光子偏振态的量子纠缠浓缩

量子纠缠浓缩可以将非最大的纠缠态转变为最大纠缠态,提高量子通信的安全性.本文基于圆偏振光和量子点-腔系统的相互作用,用一个单光子作为连接远距离纠缠光子对的桥梁,在理想条件下实现了光子偏振纠缠态的浓缩.计算结果显示,这个纠缠浓缩方案在考虑耦合强度和腔泄漏的情况下也可以保持较高的保真度,而且不需要知道部分纠缠态的初始信息,也不必重复执行纠缠浓缩过程.这不仅提高了量子纠缠浓缩的安全性,也有助于通过消耗最少的量子资源来实现高效的量子信息处理.     

Probabilistic teleportation of an unknown N-atom state using a two-atom nonmaximally entangled state in cavity QED

We present a scheme for realizing probabilistic teleportation of an unknown N-atom state via cavity QED. This scheme requires only a nonmaximally entangled pair to be used as a quantum channel, so the requirement of entanglement is reduced. In addition, our scheme does not involve the Bell-state measurement and is insensitive to the cavity decay, which is important from the experimental point of view. If the quantum channel is a two-atom maximally entangled state, teleportation of an unknown N-atom state can be realized by a simpler scheme via cavity QED.     

纠缠相干态的纠缠浓缩

利用线性光学元器件对光场量子态进行操纵,可以实现远程的量子纠缠调控和量子通讯.通过分析光学分束器对相干态光场的作用,发现当初始光场态是两个两部分纠缠态的直乘时,让其中的两模通过光学分束器作用后再对其进行光子计数,另外两模将会塌缩到新的纠缠态.基于这个特点,提出了一个实现部分纠缠相干态纠缠浓缩的方案.在这个方案中,两个部分纠缠相干态被用来作为量子信道,通过光学分束器作用后对光场进行光子数探测时,如果测量到光场的两模分别处于奇光子数态和零光子数态,则光场另外的两模将塌缩到最大纠缠态,从而完成纠缠浓缩的过程.计算结果表明,对于纠缠相干态,无论其初始的纠缠是多么微弱,利用这种方法总有一定的几率可以从中提纯出最大纠缠态.     

Effect of excess noise on continuous variable entanglement sudden death and Gaussian quantum discord

A symmetric two-mode Gaussian entangled state is used to investigate the effect of excess noise on entanglement sudden death and Gaussian quantum discord with continuous variables. The results show that the excess noise in the channel can lead to entanglement sudden death of a symmetric two-mode Gaussian entangled state, while Gaussian quantum discord never vanishes. As a practical application, the security of a quantum key distribution （QKD） scheme based on a symmetric two-mode Gaussian entangled state against collective Gaussian attacks is analyzed. The calculation results show that the secret key cannot be distilled when entanglement vanishes and only quantum discord exists in such a QKD scheme.     

Entanglement swapping of continuous variable using squeezed vacuum states

We present a realistic scheme for the entanglement swapping of continuous variable, in which a two-mode squeezed vacuum state serves as a quantum channel. The position sum and momentum difference of two local modes are measured. By taking the input entangled state also as a two-mode squeezed vacuum state, we investigate the average fidelity and the von Neumann entropy of the output state. The results show that the perfect teleportation can be achieved by increasing the squeezing of the quantum channel and that any nonzero squeezing in both the quantum channel and the input entangled state is sufficient to swap the entanglement.     

Quantum key distribution without the transfer of a quantum state as a whole through a communication channel

An example of quantum key distribution on an entangled single photon and in vacuum states is given. In this scheme, the single-photon quantum state is never transferred as a whole through a communication channel.     

Probabilistic Teleportation of Three-Qubit Entangled State via Five-qubit Cluster State

A scheme for probabilistic teleportation of an unknown three-qubit entangled state via a five-qubit non-maximally entangled cluster state as quantum channel is proposed. In this scheme, the sender performs two Bell state and a single-qubit measurements on the qubits, the receiver can reconstruct the original state with a certain probability by making appropriate unitary transformations and controlled-not (C-not) operations. As a result, the probability of successful teleportation is determined by the smallest two of the coefficients’ absolute values of the cluster state. The considerable advantage of our scheme is that we employ a non-maximally entangled cluster state as quantum channel in the scheme, which can greatly reduce the amount of entanglement resources and need less classical bits.     

Efficient Joint Remote Preparation of an Arbitrary m-qudit State with Partially Entangled States

We present an efficient scheme for multiparty joint remote preparation of an arbitrary m-qudit state by using partially entangled states as the quantum channel. One of the senders first performs a collective unitary transformation on his entangled particles and the auxiliary qubit, and then he performs a Z-basis measurement on the auxiliary qubit for transforming the partially entangled quantum channel into the two types of multi-particle entangled states. In the first case, the quantum channel shared by all the senders and the receiver is the target channel. In the second case, the quantum channel transforms into another partially entangled state which is the resource for the quantum channel transformation in the next round. Compared with other protocols, our scheme has advantage of having high success probability for joint remote preparation of an arbitrary m-qudit state via partially entangled states.     

远程制备双原子纠缠态

提出一种远程制备双原子纠缠态的方案,该方案基于两个原子与单模腔场的同时非共振相互作用.由于双粒子纠缠态比三粒子纠缠态容易制备,方案用两对双原子纠缠态作为量子通道.Alice 拥有的两个相同原子同时与一单模腔场非共振相互作用.Alice已知她要制备的纠缠态,她选择适当的相互作用时间、测量她所拥有的两个原子并通过经典通道通知Bob.Bob引入一个相同的辅助原子和一个单模腔场来实现方案.方案对腔场状态和腔损耗不敏感,基于当前的腔QED 技术,方案能在实验上实现.该方案有望在量子信息过程中有重要的应用价值.     

量子比特的普适远程翻转和克隆

提出一种把量子隐形传态、最佳普适量子比特翻转和最佳普适量子克隆三者结合起来的量子比特普适远程翻转和克隆方案.当发送者和处于不同地点的三个接收者共享一个特定的四粒子纠缠态作为量子信道时,通过发送者的Bell基测量、经典通信和各个接收者的局域幺正变换,一个接收者能够以2/3的最佳保真度得到一份原未知量子比特的正交补态,另外两个接收者能够分别以5/6的最佳保真度得到原未知量子比特的一份拷贝.此方案用较少的量子纠缠资源同时完成了未知量子比特的普适远程翻转和克隆,且其保真度分别达到了最佳.实现此方案的关键在于构造出发送者和接收者共享的特定四粒子纠缠态作为量子信道,分析了此特殊四粒子态内在的纠缠结构.     

Teleportation for an Ionic Entangled Internal State by Entanglement Swapping

We present an effective scheme to teleport an unknown ionic entangled internal state via trapped ions without joint Bell-state measurement. In the constructed quantum channel process, we adopt entanglement swapping to avoid decrease of entanglement during the distribution of particles. Thus our scheme provides new prospects for quantum teleportation over longer distance. The distinct advantages of our scheme are that our scheme is insensitive to heating of vibrational mode and can be generalized to teleport an N-ion electronic entangled GHZ class state. Furthermore, in our scheme the success probability can reach 1.     

Generation of the nonlocal quantum entanglement of three three-level particles by local operations

We propose a scheme to realize the nonlocal quantum entanglement of three three-level particles by using a three-particle entangled state of three levels as a quantum channel with the aid of some local unitary transformations. This scheme can be directly generalized to the nonlocal quantum entanglement of N three-level particles.     

Quantum state sharing of an arbitrary multiqubit state using nonmaximally entangled GHZ states

We explicitly present a scheme for quantum state sharing of an arbitrary multiqubit state using nonmaximally entangled GHZ states as the quantum channel and generalized Bell states as the measurement basis. The scheme succeeds only probabilistically with its total success probability depending on the degree of entanglement matching between the quantum channel and the generalized Bell states. Security of the scheme is guaranteed by the fact that attacks of an outside eavesdropper or/and an inside dishonest party will inevitably introduce detectable errors.     

Quantum multicast schemes of different quantum states via non-maximally entangled channels with multiparty involvement

Due to the unavoidable interaction between the quantum channel and its ambient environment, it is difficult to generate and maintain the maximally entanglement. Thus, the research on multiparty information transmission via non-maximally entangled channels is of academic value and general application. Here, we utilize the non-maximally entangled channels to implement two multiparty remote state preparation schemes for transmitting different quantum information from one sender to two receivers synchronously. The first scheme is adopted to transmit two different four-qubit cluster-type entangled states to two receivers with a certain probability. In order to improve success probabilities of such multicast remote state preparation using non-maximally entangled channels, we put forward the second scheme, which deals with the situation that is a synchronous transfer of an arbitrary single-qubit state and an arbitrary two-qubit state from one sender to two receivers. In particular, its success probability can reach 100% in principle, and independent of the entanglement degree of the shared non-maximally entangled channel. Notably, in the second scheme, the auxiliary particle is not required.