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.

Robustness of Genuine Tripartite Entanglement under Collective Dephasing

We study the robustness of genuine multipartite entanglement for a system of three qubits under collective dephasing. Using a computable entanglement monotone for multipartite systems, we find that almost every state is quite robust under this type of decoherence. We analyze random states and weighted graph states at infinity and find all of them to be 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.

Generating genuine multipartite entanglement via XY-interaction and via projective measurements

We have studied the generation of multipartite entangled states for the superconducting phase qubits. The experiments performed in this direction have the capacity to generate several specific multipartite entangled states for three and four qubits. Our studies are also important as we have used a computable measure of genuine multipartite entanglement whereas all previous studies analyzed certain probability amplitudes. As a comparison, we have reviewed the generation of multipartite entangled states via von Neumann projective measurements.

Construction of Complete Orthogonal Genuine Multipartite Entanglement State

With the development of quantum information processing, multipartite entanglement measures are needed in many cases. However, there are still no complete orthogonal genuine multipartite entanglement(GME) bases available as Bell states to bipartite systems. To achieve this goal, we find a method to construct complete orthogonal GME states, and we exclude many equivalent states by leveraging the group theory. We also provide the case of a 3-order 3-dimensional Hilbert space as an example and study the application of general results in the dense coding scheme as an application. Moreover, we discuss some open questions and believe that this work will enlighten extensive studies in this field.

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.

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.

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.

Experimental verification of genuine multipartite entanglement without shared reference frames

Quantum entanglement is an essential resource for quantum information processing, either for quantum communication or for quantum computation. The multi- partite case of entanglement, especially the so called gen- uine multipartite entanglement, has significant importance for multipartite quantum information protocols. Thus, it is a natural requirement to experimentally verify multipartite quantum entanglement when performing many quantum int^rmation tasks. However, this is often technically chal- lenging due to the difficulty of building a shared reference lYame among all involved parties, especially when these parties are distant l^om each other. In this paper, we experimentally verify the genuine tripartite entanglement of a three-photon Greenberger-Horne-Zeilinger state without shared reference frames. A high probability 0.79 of successfully verifying the genuine tripartite entanglement is achieved when no reference frame is shared. In the case of sharing only one common axis, an even higher success probability of 0.91 is achieved.

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.

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.

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.

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%.