基于高维两粒子纠缠态的超密编码方案

基于通信双方预先共享d维二粒子最大纠缠态非定域相关性,信息发送方Bob只需要向信息接收者Alice传送一个粒子,就可以传送logd22比特经典信息,为保护信息的安全,方案采用诱骗光子技术,安全性等价于改进后的原始量子密钥分配方案（Bennett-Brassard 1984,BB84）.本文讨论了基于高维纯纠缠态超密编码方案.即通过引入一个附加量子比特,信息接收方对手中的纠缠粒子和附加粒子在执行相应的幺正演化,可以获取dαk2logd2+logd2（αk=minαj,j∈0,L,d－1）比特经典信息.通信双方采用诱骗光子技术确保量子信道的安全建立.与其他方案相比,该方案具有通信效率较高、实用性较强的优点.     

基于高维两粒子纠缠态的超密编码方案

基于通信双方预先共享d维二粒子最大纠缠态非定域相关性,信息发送方Bob只需要向信息接收者Alice传送一个粒子,就可以传送log22比特经典信息,为保护信息的安全,方案采用诱骗光子技术,安全性等价于改进后的原始量子密钥分配方案(Bennett-Brassard 1984,BB84).本文讨论了基于高维纯纠缠态超密编码方...     

基于五离子最大纠缠态的优化隐形传态和超密集编码

我们提出了一个制备五离子最大纠缠态的方案,并利用该纠缠态实现任意两量子比特的隐形传送和超密集编码。超密集编码的信息容量满足Holevo bound,这意味着通过发送三个量子比特可以传送五个经典比特的信息。     

利用Raman相互作用传送两比特的未知原子态

实现量子态的隐形传送,尤其是多比特量子态的隐形传送在量子信息领域中有非常重要的作用。本文提出了一种隐形传送两比特未知原子态方案。在此方案中,用一个三粒子纠缠态作为量子信道,传送两比特未知原子态。     

利用拉曼型的Jaynes-Cummings模型传送两比特的未知原子态

实现量子态的隐形传送、尤其是多比特量子态的隐形传送在量子信息领域中有非常重要的作用，提出了一种隐形传送两比特未知原子态的方案，在此方案中，用两个两粒子纠缠态代替一个三粒子纠缠态作为量子信道，而且此方案可推广到隐形传送N比特的未知原子态。     

分离状态下的有效纠缠分配

提出采用两个量子比特（四维空间的qudit）作为分离的中间媒介实现高效的纠缠分发方案.首先,两个中间媒介量子比特与两个不同站点的量子比特(定义为a和b)形成四个量子比特非锁定束缚纠缠态,也称为Smolin态.然后,对两个附属量子比特在贝尔基矢上进行联合投影测量,测量结果传送给a和b,基于测量结果,量子比特a和b将可以转换为EPR纠缠态.在整个过程,两个附属量子比特始终与量子比特a和b保持分离.该方案提供了一种利用分离态实现最大纠缠态分发的高效方法,并且给出了公式来描述和理解该过程.     

基于腔QED的隐形传送四比特团簇类态方案

本文提出了一个基于腔QED的隐形传送四比特团簇类态方案,在该方案中选用两个GHZ纠缠对作为量子通道,通过对原子和腔场的大失谐作用以及外加强经典场的辅助,可以制备纠缠的量子通道,完成联合的三粒子测量,成功地实现隐形传送四比特团簇类态。结果还表明,此方案不受腔场退相干和热场的影响.     

基于(2m+1)粒子纠缠态的任意m粒子态量子可控离物传态(英文)

提出了一个基于高维2m+1粒子纠缠态的任意m粒子态量子可控离物传态方案,发送方Alice对需传送的未知态量子系统和手中的纠缠粒子执行m个广义Bell基测量,控制方执行广义X基测量,依据预先共享量子纠缠态非定域相关性,接收方对手中的粒子执行相应的幺正操作就可以重建原来未知量子态.与其他方案相比,方案减少了任意高维多粒子态可控离物传送所需传送粒子数.我们进一步讨论了基于纯纠缠信道的概率量子可控离物传态方案,通过与发送方和控制方合作,接收方只需对手中的纠缠粒子和引入的附加粒子执行联合幺正演化和投影测量,就可以在他的粒子上概率的重建原来的未知量子态,最后,方案计算讨论了基于纯纠缠态量子可控离物传态成功概率与信道纠缠度之间的关系.     

纠缠辅助下三方通信复杂度问题及其量子线路的研究

我们设计了一个实现纠缠辅助下计算特定布尔函数的三方通信复杂度问题的量子线路,该问题中输入变量分布在通信三方。计算分析表明如果通信三方没有分享纠缠态,需要四比特经典通信才能完成计算任务。有纠缠辅助下,仅通过三比特经典通信能够以一定概率完成任务,成功概率与纠缠态的具体形式有关,当选择合适的纠缠态时,成功概率最高可达100%。     

远程态制备和远程态测量用核磁共振实验实现

量子隐形传态利用一最大的纠缠通道,经过局域操作和经典通讯(LOCC),将任意一未知量子态从发送者(Alice)传送到远处的接收者(Bob),消耗一个纠缠比特(ebit)和两个经典比特(bit),即1ebit+2cbit*1qubit.     

Entanglement and Optimal Dense Coding in Spin Chain with an Arbitrary Magnetic Field

The entanglement and optimal dense coding at entangled states of a 1D Ising chain in the presence of an external magnetic field with an arbitrary direction, are investigated. The entanglement concurrence and the optimal dense coding capacity are calculated for different orientations of the magnetic field. It has been found that the direction of external magnetic field has effects on the entanglement concurrence and optimal dense coding capacity. In the case of antiferromagnet, the quantum phase transition occurs when an external magnetic field is parallel to Ising orientation. The concurrence increases when the angle between the direction of magnetic field and Ising orientation become smaller at ground state in certain parameter regimes, so does the optimal dense coding. The maximum moves toward the direction perpendicular to the Ising orientation in higher temperature. In contrast, the more concurrence and optimal dense coding can be produced only in the case of an external magnetic field perpendicular to Ising orientation at zero and low temperature for ferromagnetic case.     

Scheme for sharing classical information via tripartite entangled states

We investigate schemes for quantum secret sharing and quantum dense coding via tripartite entangled states. We present a scheme for sharing classical information via entanglement swapping using two tripartite entangled GHZ states. In order to throw light upon the security affairs of the quantum dense coding protocol, we also suggest a secure quantum dense coding scheme via W state by analogy with the theory of sharing information among involved users.     

Entanglement Purification of Noisy Two-Qutrit States Via Environment Measurement

Entanglement swapping combined with environment measurement is proposed to purify entanglement of two-qutrit entangled states subjected to the local individual amplitude damping channels. The resultant states of our scheme have much more entanglement even though entanglement swapping itself cannot purify entanglement. When the scheme is applied to dense coding, the dense coding capacity can be significantly improved.     

Remote State Preparation with Genuine Multipartite Entanglement

Enlightened by the work of Yeo and Chua [Phys. Rev. Lett. 96 （2006） 060502] for teleportation and dense coding with genuine multipartite entanglement, we present an explicit protocol for faithful remote state preparation in a real coefficient case by using the same four-particle entangled state which is not reducible to pair of Bell states. It is shown that any complex coefficient case can be changed to a real coefficient case. With this protocol, the state can play an analogous role to Einstein-Podolsky-Rosen pairs in the theory of multipartite entanglement.     

The fully entangled fraction as an inclusive measure of entanglement applications

Characterizing entanglement in all but the simplest case of a two qubit pure state is a hard problem, even understanding the relevant experimental quantities that are related to entanglement is difficult. It may not be necessary, however, to quantify the entanglement of a state in order to quantify the quantum information processing significance of a state. It is known that the fully entangled fraction has a direct relationship to the fidelity of teleportation maximized under the actions of local unitary operations. In the case of two qubits we point out that the fully entangled fraction can also be related to the fidelities, maximized under the actions of local unitary operations, of other important quantum information tasks such as dense coding, entanglement swapping and quantum cryptography in such a way as to provide an inclusive measure of these entanglement applications. For two qubit systems the fully entangled fraction has a simple known closed-form expression and we establish lower and upper bounds of this quantity with the concurrence. This approach is readily extendable to more complicated systems.     

Perfect quantum teleportation and dense coding protocols via the 2N-qubit W state

In this paper, we investigate perfect quantum teleportation and dense coding by using an 2N-qubit W state channel. In the quantum teleportation scheme, an unknown N-qubit entangled state can be perfectly teleported. One ebit of entanglement and two bits of classical communication are consumed in the teleportation process, just like when using the Bell state channel. While N+1 bits of classical information can be transmitted by only sending N particles in the dense coding protocol.     

Dense Coding with Multi-Atom Entanglement Channel in Cavity QED

Dense coding of multi-atom entangled states in cavity QED is studied. If the quantum channel is generalized GHZ states, dense coding can be directly realized in a simply way. As for the partially entangled pure states, we propose a feasible protocol for entanglement concentration, and the emciency of information transmitted is calculated. The schemes are insensitive to the cavity decay and the field state, due to the fact that the interaction here is a large-detuned one between atoms and the cavity.     

Experimental demonstration of tripartite entanglement and controlled dense coding for continuous variables

A tripartite entangled state of bright optical field is experimentally produced using an Einstein-Podolsky-Rosen entangled state for continuous variables and linear optics. The controlled dense coding among a sender, a receiver, and a controller is demonstrated by exploiting the tripartite entanglement. The obtained three-mode "position" correlation and relative "momentum" correlation between the sender and the receiver, and thus the improvements of the measured signal to noise ratios of amplitude and phase signals with respect to the shot noise limit are 3.28 and 3.18 dB, respectively. If the mean photon number n equals 11 the channel capacity can be controllably inverted between 2.91 and 3.14. When n is larger than 1.0 and 10.52, the channel capacity of the controlled dense coding is predicted to exceed the ideal single channel capacity of coherent and squeezed state light communication, respectively.     

Teleportation and dense coding with genuine multipartite entanglement

We present an explicit protocol E0 for faithfully teleporting an arbitrary two-qubit state via a genuine four-qubit entangled state. By construction, our four-partite state is not reducible to a pair of Bell states. Its properties are compared and contrasted with those of the four-party Greenberger-Horne-Zeilinger and W states. We also give a dense coding scheme D0 involving our state as a shared resource of entanglement. Both D0 and E0 indicate that our four-qubit state is a likely candidate for the genuine four-partite analogue to a Bell state.     

Controlled Dense Coding with Five-Qubit Cluster State

Two schemes, via entanglement concentration and with generalized measurement respectively, for controlled dense coding with a one-dimensional five-qubit cluster state are investigated. In this protocol, the supervisor (Cliff) can control the entanglement of the channel and the average amount of information transmitted from the sender (Alice) to the receiver (Bob) by adjusting the local measurement angle θ. It is shown that the results for the average amounts of information are unique from the different two schemes.