Long-distance quantum teleportation assisted with free-space entanglement distribution

Faithful long-distance quantum teleportation necessitates prior entanglement distribution between two communicated locations. The particle carrying on the unknown quantum information is then combined with one particle of the entangled states for Bell-state measurements, which leads to a transfer of the original quantum information onto the other particle of the entangled states. However in most of the implemented teleportation experiments nowadays, the Bell-state measurements are performed even before successful distribution of entanglement. This leads to an instant collapse of the quantum state for the transmitted particle, which is actually a single-particle transmission thereafter. Thus the true distance for quantum teleportation is, in fact, only in a level of meters. In the present experiment we design a novel scheme which has overcome this limit by utilizing fiber as quantum memory. A complete quantum teleportation is achieved upon successful entanglement distribution over 967 meters in public free space. Active feed-forward control techniques are developed for real-time transfer of quantum information. The overall experimental fidelities for teleported states are better than 89.6%, which signify high-quality teleportation.     

Teleportation of a three—particle entangled W state

We have investigated the problem of teleporting a three-particle entangled W state and we propose a scheme based on entanglement spapping to complete the teleportation.We also put forward a scheme for the teleportation of a general W state by using nonmaximally entangled quantum channels.The probability of success of the latter scheme is obtained.     

Thermal entanglement and teleportation of a thermally mixed entangled state of a Heisenberg chain through a Werner state

The thermal entanglement and teleportation of a thermally mixed entangled state of a two-qubit Heisenberg XXX chain under the Dzyaloshinski Moriya （DM） anisotropic antisymmetric interaction through a noisy quantum channel given by a Werner state is investigated. The dependences of the thermal entanglement of the teleported state on the DM coupling constant, the temperature and the entanglement of tbe noisy quantum channel are studied }n detail for both the ferromagnetic and the antiferromagnetic cases. The result shows that a minimum entanglement of the noisy quantum channel must be provided in order to realize the entanglement teleportation. The values of fidelity of the teleported state are also studied for these two cases. It is found that under certain conditions, we can transfer an initial state with a better fidelity than that for any classical communication protocol.     

三粒子纠缠相干态的隐形传态

提出了一个利用一个两粒子最大纠缠相干态和一个三粒子纠缠相干态作为量子信道进行三粒子纠缠相干态隐形传态的方案.该方案只需线性光学操作和双模光子数测量.计算结果表明,应用本方案的设置,隐形传态成功的概率与所用的相干态的平均光子数有关,反映了纠缠相干态的非正交特性.     

Quantum Teleportation Through a Two-Qubit Heisenberg XXZ Chain

We consider a two-qubit Heisenberg XXZ chain as a resource for quantum teleportation via the standard teleportation protocol To. The effects of anisotropic on teleportation fidelity and entanglement are studied in detail. We find anisotropic not only improves the criticM temperature Tc and criticM magnetic field Bc, beyond which quantum teleportation is inferior to classicM communication protocol, but also enhances the fidelity for fixed magnetic field B and temperature T. For entanglement teleportation, the effects of magnetic field on average fidelity and output entanglement are studied.     

Short-Distance Teleportation of an Arbitrary Two-Qubit State Via a Bell State

We propose a scheme for teleportation of an arbitrary two-qubit state by using a Bell state as the quantum channel working together with an auxiliary qubit. Our scheme needs less entanglement resource, but at the cost of shortening teleportation distance. This is because that in order to successfully recover the teleported state, both sender and receiver need to implement quantum-gate operations on the shared auxiliary qubit. So, the auxiliary qubit must be close to both sender and receiver. Otherwise, the sender and receiver cannot carry out quantum-gate operations on it. Thus, our scheme is invalid for long-distance teleportation. But for short-distance teleportation, our scheme is an optimal choice because it requires less entanglement resource. From a practical point of view, our scheme is very promising for application in quantum teleportation on chip.

     

连续变量量子离物传态的实验研究

利用单个Ⅱ类相位匹配OPA产生的双模压缩态实现连续变量压缩纠缠态，完成了连续变量量 子离物传态. Ⅱ类相位匹配OPA参量反放大过程可以实现正交振幅反关联、正交位相关联的 压缩纠缠态，这不同于一般运转于阈值以下的OPO产生的正交振幅关联、正交位相反关联的 压缩纠缠态，可以采用直接平衡测量的方法完成Bell态测量. 利用双KTP补偿非线性过程的 离散效应，获得了最大压缩大于2dB的双模压缩纠缠态，实现保真度06，考虑到探测效率 实际保真度为057. 这种方案简化了测量方法与纠缠光源产生装置，有利于进行量子通信 的实验研究与应用. 同时，讨论了探测过程中的一些非理想因素. 关键词： 量子离物传态 压缩纠缠态 Bell态测量     

Standard Teleportation of One-Qubit State and Partial Teleportation of Two-Qubit State via X-States

In this article,we derive the explicit entanglement and fidelity expressions for a larger class of two-qubit states,namely,a seven-parameter family of so called X-states.The analytical expressions of the entanglement,the output entanglement and the average fidelity are obtained for this general model by using the concept of concurrence and average fidelity.We study the relations between quantum entanglement,the output entanglement,and the average fidelity for standard teleportation of one-qubit and partial teleportation of two-qubit state.We discover that the average fidelity and entanglement is not a simple dependence relation.The higher entangled system is helpful for teleportation.     

振幅阻尼信道量子隐形传态保真度恢复机理

在振幅阻尼信道上进行量子隐形传态的过程中, 量子Bell纠缠态将发生退相干, 导致隐形传态质量下降甚至通信失败. 为克服该影响, 本文提出了一种Bell纠缠态补偿方法. 在估计振幅阻尼信道参数的基础上, 将对纠缠态的补偿分为纠缠退相干发生之前的预补偿以及 经历量子振幅阻尼信道之后的匹配补偿两部分. 前者在纠缠源处进行, 后者在两个量子通信 用户处进行, 预补偿及匹配补偿参数与信道特性参数相关. 纠缠补偿完成后, 再进行隐形传态. 理论推导与性能分析结果表明, 相比于不进行纠缠补偿及仅在发生退相干之后进行的纠缠补偿, 本方法能够获得更高的隐形传态保真度, 适当调整补偿参数, 可使保真度接近于1, 对克服纠缠 退相干带来的隐形传态质量下降问题具有一定的意义.     

Controlled Teleportation of Multi-qudit Quantum Information by Entanglement Swapping

In this paper, we present a scheme for teleporting multi-qudit quantum state, from the sender Alice to the receiver Charlie via many controllers Bobs, whose control parameters are obtained using entanglement swapping of maximally d-dimensional EPR pair. In our scheme, Yang＇s qutrit controlled teleportation protocol [Commun. Theor. Phys. 49 （2008） 338] based on Bell-state entanglement swapping is generalized to the qudit case. The scheme of multi-qudit owns the advantage of having higher code capacity and better security than that of multi-qutrit.     

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.     

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.     

由光分束器和起偏器混合产生的三模纠缠态表象

在三模Fock空间中,本文构建了一种新的三模连续变量纠缠态,它构成了一个新的量子力学表象.该态可以利用非对称光束分离器和起偏器实现.态的纠缠性通过获得其相应的施密特分解得以说明.作为该表象的一个重要应用,利用它实现了单粒子态的量子隐态传输,给出了相应的传输方案. 关键词： 三模连续纠缠态表象 有序算符内的积分技术 量子纠缠 量子隐态传输     

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.     

多光子纠缠实验新进展--五光子纠缠技术及终端开放的隐形传态实验

在实验上发展了多光子纠缠技术,利用已有的四光子纠缠技术结合新发展的单光子源技术,在世界上第一次实现了五光子纠缠．并在此基础上实现了新型的量子隐形传态——终端开放的隐形传态．实验结果在量子力学基础问题的检验、信息论、密码学和量子计算等重要应用方向上,都具有显著的意义和价值．实验方法将大大促进未来网络化量子通信、线性光学量子计算、量子力学基础检验等重要科学问题的研究。     

多跳噪声量子纠缠信道特性及最佳中继协议

在量子通信网络中, 最佳中继路径的计算与选择策略是影响网络性能的关键因素. 针对噪声背景下量子隐形传态网络中的中继路径选择问题, 本文首先研究了相位阻尼信道及振幅阻尼信道上的纠缠交换过程, 通过理论推导给出了两种多跳纠缠交换信道上的纠缠保真度与路径等效阻尼系数. 在此基础上提出以路径等效阻尼系数为准则的隐形传态网络最佳中继协议, 并给出了邻居发现、量子链路噪声参数测量、量子链路状态信息传递、中继路径计算与纠缠资源预留等工作的具体过程. 理论分析与性能仿真结果表明, 相比于现有的量子网络路径选择策略, 本文方法能获得更小的路径平均等效阻尼系数及更高的隐形传态保真度. 此外, 通过分析链路纠缠资源数量对协议性能的影响, 说明在进行量子通信网设计时, 可以根据网络的规模及用户的需求合理配置链路纠缠资源.     

基于GHZ纠缠态实现纯EPR对的双向量子隐形传态

提出了一种基于Greenberger-Horne-Zeilinger(GHZ)纠缠态进行纯EPR对双向隐形传态的方案.通过使用纠缠交换技术,通信双方Alice和Bob共享两对三粒子GHZ纠缠态来构建量子信道.方案中通过使用受控非门操作,单量子位测量以及适当的幺正操作,通信双方可以同时发送一个纯EPR对给对方.故相比仅可以传送单一量子态的方案更经济.     

Quantum logic networks for probabilistic teleportation

By eans of the primitive operations consisting of single-qubit gates.two-qubit controlled-not gates,Von Neuman measurement and classically controlled operations.,we construct efficient quantum logic networks for implementing probabilistic teleportation of a single qubit,a two-particle entangled state,and an N-particle entanglement.Based on the quantum networks,we show that after the partially entangled states are concentrated into maximal entanglement,the above three kinds of probabilistic teleportation are the same as the standard teleportation using the corresponding maximally entangled states as the quantum channels.     

基于W态的跨中心量子网络身份认证方案

利用量子隐形传态原理和量子纠缠交换技术,提出了基于W态的跨中心量子网络身份认证方案,实现了分布式量子通信网络中对客户的身份认证.该方案分为注册阶段和身份认证阶段,认证系统包括主服务器和客户端服务器.客户所有的操作都在客户端服务器上进行,不直接与主服务器进行通信.身份认证全部由服务器根据量子力学原理进行,保证了认证方案的安全性.最后,对该方案进行了安全性分析.     

单-双模组合压缩热态的纠缠性质及在量子隐形传态中的应用

基于单-双模组合压缩真空态一定范围内能够获得压缩增强的效果,引入单-双模组合压缩热态(DSMST),讨论其纠缠性质.利用Weyl编序算符在相似变换下的不变性,简洁方便地导出了DSMST的纠缠度-负对数值,并给出了当热效应存在时保持纠缠的条件.研究表明:与通常的双模压缩态相比,随着参数的增加,DSMST的纠缠度增加.作为DSMST的应用,利用其实现相干态的量子隐形传输.结果表明:不同于纠缠度随压缩参数增加,保真度获得改善是有条件的,该条件恰好就是一正交分量涨落出现压缩增强的参数区域.此外,解析推导了有效隐形传输保真度(1/2)的条件.