利用两能级原子与腔场相互作用实现纠缠压缩态的纠缠浓缩

根据大失谐条件下原子-腔场相互作用的特点,讨论了一个制备纠缠压缩态的方法,提出了一个利用两能级原子与腔场相互作用实现纠缠压缩态纠缠浓缩的方案。在这个方案中,两束具有相同振幅但有着 相位差的压缩光 和 构成的纠缠态光场被用来作为量子信道。通过利用两能级原子与腔场的相互作用以及两模正交态测量实现了这个纠缠浓缩的过程。结果表明：对于纠缠压缩态,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部分纠缠态中提取出最大纠缠态。     

Calculation of Entanglement Entropy for Continuous-Variable Entangled State Based on General Two-Mode Boson Exponential Quadratic Operator in Fock Space

We obtain an explicit formula to calculate the entanglement entropy of bipartite entangled state of general two-mode boson exponential quadratic operator with continuous variables in Fock space. The simplicity and generality of our formula are shown by some examples.     

Teleportation of N-Particle Entangled GHZ State via Entanglement Swapping

In this scheme, N non-maximally entangled particle pairs are used as quantum channel to teleport an unknown N-particle entangled GHZ state via entanglement swapping. In order to realize this teleportation, the sender Alice operates Bell-state measurement on particles belonging to herself. Then she informs the results to the receiver Bob through classical communication. According to the results, Bob operates corresponding transformation to reconstruct the initial state. The advantage of this scheme is that it needs only one common unitary matrix for Alice‘s different results, which has a more general meaning. As a special case, teleporting an unknown three-particle entangled GHZ state is proposed.     

Teleportation of N-Particle Entangled GHZ State via Entanglement Swapping

In this scheme, N non-maximally entangled particle pairs are used as quantum channel to teleport an unknown N-particle entangled GHZ state via entanglement swapping. In order to realize this teleportation, the sender Alice operates Bell-state measurement on particles belonging to herself. Then she informs the results to the receiver Bob through classical communication. According to the results, Bob operates corresponding transformation to reconstruct the initial state. The advantage of this scheme is that it needs only one common unitary matrix for Alice＇s different results, which has a more general meaning. As a special case, teleporting an unknown three-particle entangled GHZ state is proposed.     

Thermal Entangled Quantum Refrigerator Working with Three-Qubit Heisenberg XX Model

An entangled quantum refrigerator working with a three-qubit one-dimensional isotropic Heisenberg XX model in a constant external magnetic field is constructed in this paper. Based on the quantum first law of thermodynamics, the expressions for several basic thermodynamic quantities such as the heat transferred, the net work and the coefficient of performance are derived. Moreover, the influence of the thermal entanglement on the basic thermodynamic
quantities is investigated. Several interesting features of the variation of the basic thermodynamic quantities with the thermal entanglement in zero and nonzero magnetic field are obtained.     

Detection of Tripartite Genuine Entanglement by Two Bipartite Entangled States

There are practical motivations to construct genuine tripartite entangled states based on the collective use of two bipartite entangled states. Here, the case that the states are two‐qubit Werner states is considered. The intervals of parameters of two‐qubit Werner states are revealed such that the tripartite state is genuinely entangled. Furthermore, we also investigate the lower bound of genuine multipartite entanglement concurrence for tripartite qudit states. Several examples are given to show the effectiveness of the lower bound.     

增光子二模纠缠相干态的纠缠特性及其通过腔量子电动力学的制备

分析了增光子二模纠缠相干态的纠缠特性,得到共生纠缠度的解析表示式.结果表明:增光子二模纠缠相干态的共生纠缠度与叠加态的相位有非常灵敏的关系.提出了一种制备增光子相干态和增光子二模纠缠相干态的方法,其制备过程为首先把增光子相干态转化为相干态与真空态一种特殊的叠加态(叠加系数与相干态振幅有关),再通过位于高Q腔内的原子与经典激光场的相互作用,从而实现增光子相干态的制备.通过一个飞行原子先后与两个光腔中光场相互作用可以实现增光子二模纠缠相干态的制备.     

Entanglement of Para-Bose Entangled Coherent States and Probabilistic Teleportation

We study the entanglement of the para-Bose entangled coherent states by adopting the entanglement of formation and propose a scheme of probabilistic teleportation via para-Bose entangled coherent states. It is found that the mean fidelity of the scheme increases with the decrease of the para-Bose parameter ho in the case of non-maximally entangled para-Bose entangled coherent states.     

增光子二模纠缠相干态的纠缠特性及其通过腔量子电动力学的制备

分析了增光子二模纠缠相干态的纠缠特性,得到共生纠缠度的解析表示式.结果表明:增光子二模纠缠相干态的共生纠缠度与叠加态的相位有非常灵敏的关系.提出了一种制备增光子相干态和增光子二模纠缠相干态的方法,其制备过程为首先把增光子相干态转化为相干态与真空态一种特殊的叠加态(叠加系数与相干态振幅有关),再通过位于高Q腔内的原子与经典激光场的相互作用,从而实现增光子相干态的制备.通过一个飞行原子先后与两个光腔中光场相互作用可以实现增光子二模纠缠相干态的制备.     

耦合系数对Tavis-Cummings模型中三体纠缠态纠缠量的影响

研究了两个全同二能级原子与单模场相互作用的Tavis-Cummings模型中的量子纠缠.在两原子初始时处于基态,光场处于单光子状态下,得出体系状态演化为近似W纠缠态.结果表明:两原子耦合量越大,三体纠缠态中两两纠缠量和三体纠缠量越小,其中两原子间纠缠量和三体纠缠量减小的程度更大,并且三体纠缠态中两两纠缠量和三体纠缠量的振荡周期也相应减小.     

未知EPR态及其正交态的概率复制

纠缠态在量子计算和量子信息中起着十分重要的作用。利用部分纠缠态作为资源提出了一种方案,根据该方案,能够以某些概率成功地复制出未知的EPR(Einstein Podolsky Rosen)态和它的正交态,使得通信双方都能够获得要传送的EPR态。方案的第一步是采用部分纠缠态作为量子信道去实现EPR态的隐形传态。根据量子不可克隆定理,输入态在发送方受到破坏。方案的第二步通过引入一个辅助量子位,发送者Alice在态的配制者Victor的帮助下,将以联合概率成功地获得未知EPR态和它的正交态。从而实现了量子态的重建。     

连续变量量子纠缠态的非对称量子克隆

该文讨论了连续变量量子纠缠态非对称克隆过程,从理论上讨论了在Local e-cloner方案中,入射和出射分束器的反射率可变情况下的纠缠态克隆,并利用纠缠不可分判据分析了所获得的非对称克隆纠缠态的纠缠特性.结果指出,克隆得到的两组纠缠态的纠缠特性不相同.     

利用四粒子纠缠态实现单粒子信息分裂

我们提出了一个在三者之间利用四粒子纠缠态作为量子通道实现对任意单粒子态的信息分裂的方案.在我们的方案中,两个接收方之间有且只有在对方提供合作的情况下才能全部获得这个原始信息,而且接收方彼此之间都有同等权限去获得该原始信息,他们获得原始信息的概率是一样的,均为1.     

Multi-Party Quantum Private Comparison Protocol Based on Entanglement Swapping of Bell Entangled States

Recently, Liu et al. proposed a two-party quantum private comparison (QPC) protocol using entanglement swapping of Bell entangled state (Commun. Theor. Phys. 57 (2012) 583). Subsequently, Liu et al. pointed out that in Liu et al.'s protocol, the TP can extract the two users' secret inputs without being detected by launching the Bell-basis measurement attack, and suggested the corresponding improvement to mend this loophole (Commun. Theor. Phys. 62 (2014) 210). In this paper, we first point out the information leakage problem toward TP existing in both of the above two protocols, and then suggest the corresponding improvement by using the one-way hash function to encrypt the two users' secret inputs. We further put forward the three-party QPC protocol also based on entanglement swapping of Bell entangled state, and then validate its output correctness and its security in detail. Finally, we generalize the three-party QPC protocol into the multi-party case, which can accomplish arbitrary pair's comparison of equality among K users within one execution.     

利用部分纠缠的特殊二粒子W态和部分纠缠的二粒子态传送二粒子纠缠态

提出了利用部分纠缠的特殊二粒子W态和部分纠缠的二粒子态组成量子信道,隐形传送一个二粒子纠缠态的方案。发送者进行两次Bell基测量,接受者先在{|0〉,|1〉}基下进行一次测量,然后实施一次控制—非操作,最后引进一个辅助粒子并进行一组适当的幺正变换操作,便可以一定的概率实现二粒子纠缠态的隐形传送。分析表明:当量子信道处于最大纠缠,即信道由一个特殊二粒子W态和一个Bell态组成时,本方案的传输概率达到2/3,传输效果介于完全由W态组成量子信道与完全由Bell态组成量子信道的方案之间。     

二粒子纠缠态受控传递的最佳量子通道

本文研究了如何在二粒子纠缠态的量子受控传递中选择最佳量子通道的问题。分别利用四粒子GHZ态和四粒子特殊"反关联GHZ态"作为量子通道,本文提出了二粒子反关联纠缠态的量子受控传递的两个方案。通过对比两个方案下接受者最后采取的幺正操作的具体矩阵形式,分析了待传量子纠缠态与量子通道的关系,指出了四粒子GHZ态和四粒子特殊"反关联GHZ态"分别是二粒子正关联和反关联纠缠态各自隐形传递应该选择的最佳的量子通道。     

Quantum Secure Direct Communication with Four-Particle Genuine Entangled State and Dense Coding

A quantum secure direct communication scheme using dense coding is proposed. At first, the sender (Alice) prepares four-particle genuine entangled states and shares them with the receiver (Bob) by sending two particles in each entangled state to him. Secondly, Alice encodes secret information by performing the unitarytransformations on her particles and transmits them to Bob. Finally, Bob performs the joint measurements on his particles to decode the secret information. The two-step security test guarantees the security of communication.