Schemes for Splitting Quantum Information with Four-Particle Genuine Entangled States

We propose two schemes for splitting single- and two-qubit states by using four-particle genuine entangled state as the quantum channel. After the sender performs Bell-basis （or three-partite GHZ- basis） measurements on her particles, and the cooperators operate single-particle measurements on their particles, the state receiver can reconstruct the original state of the sender by applying the appropriate unitary operation. In particular, in the scheme for splitting two-qubit state, the receiver needs to introduce an auxiliary particle and carries out a C-NOT operation.

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 eachentangled state to him.Secondly,Alice encodes secret information by performing the unitary transformations on herparticles and transmits them to Bob.Finally,Bob performs the joint measurements on his particles to decode the secretinformation.The two-step security test guarantees the security of communication.

Deterministic Joint Remote Preparation of Arbitrary Four-Particle Genuine Entangled State

A novel deterministic joint remote preparation scheme of arbitrary four-particle genuine entangled state from one sender to either of two receivers is proposed. Two three-particle Green-Horne-Zeilinger （GHZ） states and one four-particle GHZ state are used as the quantum channel. The presented scheme is realized through orthogonal projective mea-surement of the Hadamard transferred basis and recovery operation Ulijk）. Some useful and general measurement bases have been con-structed. The classical communication cost of the presented scheme is also calculated. Our analysis confirms the feasibility and validity of the proposed method, and shows that it has a 100% probability of success in preparation of the target quantum state.

Preparation of Genuinely Entangled Six-Atom State via Cavity Quantum Electrodynamics

A cavity quantum electrodynamics scheme for preparing a genuinely entangled state [A. Borras, et al., J. Phys. A 40 （2007） 13407] on six two-level atoms is proposed. In the scheme, the atom-cavity detuning is much bigger than the atom-cavity coupling strength and the necessary preparation time is much shorter than the Rydberg-atom lifespan. Hence the scheme has two distinct features, i.e., insensitive to the cavity decay and the atom radiation.

Genuine entanglement under squeezed generalized amplitude damping channels with memory

We study genuine entanglement among three qubits undergoing a noisy process that includes dissipation, squeezing,and decoherence. We obtain a general solution and analyze the asymptotic quantum states. We find that most of these asymptotic states can be genuinely entangled depending upon the parameters of the channel, memory parameter, and the parameters of the initial states. We study Greenberger–Horne–Zeilinger(GHZ) states and W states, mixed with white noise,and determine the conditions for them to be genuinely entangled at infinity. We find that for these mixtures, it is possible to start with a bi-separable state(with a specific mixture of white noise) and end with genuine entangled states. However, the memory parameter μ must be very high. We find that in contrast to the two-qubit case, none of the three-qubit asymptotic states for n → ∞ are genuinely entangled.

Measures of genuine multipartite entanglement for graph states

Graph states are special multipartite entangled states that have been proven useful in a variety of quantum information tasks. We address the issue of characterizing and quantifying the genuine multipartite entanglement of graph states up to eight qubits. The entanglement measures used are the geometric measure, the relative entropy of entanglement, and the logarithmic robustness, have been proved to be equal for the genuine entanglement of a graph state. We provide upper and lower bounds as well as an iterative algorithm to determine the genuine multipartite entanglement.

Perfect teleportation of an arbitrary three-qubit state with the highly entangled six-qubit genuine state

The perfect teleportation of an arbitrary three-qubit state with the highly entangled six-qubit genuine state introduced by Borras et al.(J.Phys.A: Math.Theor.40 (2007) 13407) is studied.Some appropriate measuring bases the sender can take and the corresponding unitary operations the receiver should execute in terms of the sender’s measurement outcome are explicitly given.The flexibility between the measurement difficulty and the reconstruction difficulty is shown.Moreover,discussions and comparisons between our scheme and the recent incomplete scheme (Choudhury et al,J.Phys.A: Math.Theor.42 (2009) 115303) are made.

Quantum Private Comparison of Equal Information Based on Highly Entangled Six-Qubit Genuine State

Using the highly entangled six-qubit genuine state we present a quantum private comparison(QPC)protocol, which enables two users to compare the equality of two bits of their secrets in every round comparison with the assistance of a semi-honest third party(TP). The proposed protocol needs neither unitary operations nor quantum entanglement swapping technology, both of which may consume expensive quantum devices. Single particle measurements and Bell-basis measurements, which are easy to implement with current technologies, are employed by two users and TP in the proposed protocol, respectively. The proposed protocol can withstand all kinds of outside attacks and participant attacks. Moreover, none of information about the two users' private secrets and the comparison result is leaked out to TP.

Generation of a Genuine Six-Atom Entangled State in Cavity QED

We propose a potential scheme to generate a genuine six-atom entangled state [J. Phys. A 42 (2009) 415301] by using atoms in cavity QED system, where the atoms interact simultaneously with the highly detuned single-mode cavity and the strong classical driving field. Thus our approach is insensitive to both the cavity decay and thermal field.

Simulation of the Ising model, memory for Bell states and generation of four-atom entangled states in cavity QED

A scheme is proposed to simulate the Ising model and preserve the maximum entangled states (Bell states) in cavity quantum electrodynamics (QED) driven by a classical field with large detuning. In the strong driving and large-detuning regime, the effective Hamiltonian of the system is the same as the standard Ising model, and the scheme can also make the initial four Bell states of two atoms at the maximum entanglement all the time. So it is a simple memory for the maximal entangled states. The system is insensitive to the cavity decay and the thermal field and more immune to decoherence. These advantages can warrant the experimental feasibility of the current scheme. Furthermore, the genuine four-atom entanglement may be acquired via two Bell states through one-step implementation on four two-level atoms in the strong-driven model, and when two Greenberger-Horne-Zeilinger (GHZ) states are prepared in our scheme, the entangled cluster state may be acquired easily. The success probability for the scheme is 1.

利用最大真纠缠六方态共享经典秘密信息

纠缠是一种重要的量子信息资源,Bell态、GHZ态等纠缠态被广泛用于量子秘密共享中。Borras等人发现的最大真六方纠缠态在任意的双方割之间具有最大的纠缠值,已经被证明可用于量子隐形传态,并表现良好的性质。通过分析Borras态的结构,利用广义Schmidt分解工具,构造了一个具体的量子秘密共享协议:事先在Alice和4个代理之间共享一个Borras纠缠态,Alice拥有其中2个qubit,代理们分别拥有它的1个qubit,则Alice可在代理间共享2bit经典信息。

基于七粒子纠缠态实现受控双向非对称隐形传态

基于一个真七粒子纠缠态,提出了两个新的双向非对称受控量子隐形传态方案.第一个方案实现一方传输一个单qubit态而另一方同时传输一个2-qubit态;第二个方案实现双方分别同时传输一个2-qubit态,其中一个是任意形式的2-qubit态,另一个是Schmidt形式的2-qubit态.方案中,参与者1和2分别对各自手中的粒子使用Bell基或GHZ基进行联合测量,并把测量结果发送给对方;而监督者使用X算子基对他的qubit进行单qubit测量,并把测量结果发送给两个参与者;之后参与者在自己的部分粒子上应用适当的酉算子运算就可以恢复出对方隐形传输的量子态.与其它方案相比,所提出方案通信效率较高,且所使用的真七粒子纠缠态制备线路简单,易于实现.

关于量子态的真多体非局域性的一些研究

基于真多体纠缠态的定义和性质,引入了量子态真多体非局域性的定义,讨论了真多体非局域量子态与真多体纠缠态的关系,给出了三类不能用来检测量子态真多体非局域性的测量集合.

以真六量子纠缠态为信道的双向受控远程态制备

研究了真六量子比特纠缠态在双向量子受控远程态制备中的一个新应用。在协议中,远程的两方在遥远的第三方控制下,能够同时地、确定地交换他们的量子态。如果没有控制者的允许,这种交换是不能成功的,而作为原始的非局域量子资源的一个真六量子比特纠缠态是预先被三方共享的。

基于6粒子纠缠态的未知单粒子态量子信息共享

以6粒子纠缠态为量子信道,提出了一个单粒子未知态的量子信息共享方案.首先信息发送者对手中的粒子进行Bell基测量和单粒子测量,接着合法双方的任意一方对自己拥有的粒子做一次单粒子测量,则另一方对自己拥有的粒子进行适当的幺正变换,就可以重建原始粒子态,从而实现了量子信息共享.该方案成功的概率为100%.

多体量子系统中量子可分态的分类

为了研究多体量子系统中量子态的可分性,利用Bell不等式给出了多体量子可分态的所有分类.这些不等式能分类22222量子系统中所有可能的k-可分量子态,包括全可分、双可分、三可分、四可分.利用推广的Bell算子和真纠缠分类,运用Cauchy-Schwarz不等式、线性规划等方法,给出了Bell算子平均值的绝对值上界,实现了多体可分态的分类.

基于5粒子纠缠态实现单粒子任意态的量子信息共享

通过对Brown等人介绍的5粒子纠缠态的新应用研究,利用5粒子纠缠态作为量子信道提出了一个单粒子任意态的信息共享方案.首先,发送者对自己拥有的粒子做一次4粒子von-Neumann联合测量.然后,控制者对其拥有的粒子做单粒子测量.接受者根据发送者和控制者的测量结果,对自己拥有的粒子做适当的幺正变换,就可以重建发送者的单粒子任意态.方案成功的概率为100%.

基于真9-qubit纠缠态实现受控双向量子隐形传态

最近,基于多方纠缠态的双向受控隐形传态受到广泛关注,多个基于五方纠缠态、六方纠缠态、七方纠缠态的双向受控隐形传态方案相继被提出.本文研究了真9-qubit纠缠态对于双向受控隐形传态的有用性,提出了两个基于真9-qubit纠缠态的双向受控隐形传态方案:一个方案实现一方传输未知的任意单qubit态而另一方传输未知的任意3-qubit态;另一个方案实现双方分别传输一个未知的任意2-qubit态.与其他基于多方纠缠态的方案相比,我们的方案其信道容量更大,一次能够双向共传输4个任意的qubit态,其通信效率也更高,而且使用的真9-qubit纠缠态易于通过Hadamard门以及受控非门等简单的量子门电路实现.

以真五粒子非最大纠缠态为信道的双向受控隐形传态

利用投影测量和正算子值测量,分别提出了以真五粒子非最大纠缠态为信道的双向受控隐形传态的两个协议。协议中,作为量子信道的真五粒子非最大纠缠态连接3个合法的参与者;在监督者Charlie的控制下,Alice以一定概率将任意未知单粒子A的态传给Bob,同时Bob也以一定概率将任意未知单粒子B的态传给Alice。这两个协议都是确定性双向隐形传态的推广。