Efficient quantum dialogue using entangled states and entanglement swapping without information leakage

We propose a novel quantum dialogue protocol by using the generalized Bell states and entanglement swapping. In the protocol, a sequence of ordered two-qutrit entangled states acts as quantum information channel for exchanging secret messages directly and simultaneously. Besides, a secret key string is shared between the communicants to overcome information leakage. Different from those previous information leakage-resistant quantum dialogue protocols, the particles, composed of one of each pair of entangled states, are transmitted only one time in the proposed protocol. Security analysis shows that our protocol can overcome information leakage and resist several well-known attacks. Moreover, the efficiency of our scheme is acceptable.     

Schemes generating entangled states and entanglement swapping between photons and three-level atoms inside optical cavities for quantum communication

We propose quantum information processing schemes based on cavity quantum electrodynamics (QED) for quantum communication. First, to generate entangled states (Bell and Greenberger–Horne–Zeilinger [GHZ] states) between flying photons and three-level atoms inside optical cavities, we utilize a controlled phase flip (CPF) gate that can be implemented via cavity QED). Subsequently, we present an entanglement swapping scheme that can be realized using single-qubit measurements and CPF gates via optical cavities. These schemes can be directly applied to construct an entanglement channel for a communication system between two users. Consequently, it is possible for the trust center, having quantum nodes, to accomplish the linked channel (entanglement channel) between the two separate long-distance users via the distribution of Bell states and entanglement swapping. Furthermore, in our schemes, the main physical component is the CPF gate between the photons and the three-level atoms in cavity QED, which is feasible in practice. Thus, our schemes can be experimentally realized with current technology.     

Fault tolerant quantum key distributions using entanglement swapping of GHZ states over collective-noise channels

This work proposes two fault tolerant quantum key distribution (QKD) protocols. Each of which is robust under one kind of collective noises: collective-dephasing noise and collective-rotation noise, respectively. Due to the use of the entanglement swapping of Greenberger–Horne–Zeilinger (GHZ) state as well as the decoy logical qubits, the new protocols provide the best qubit efficiency among the existing fault tolerant QKD protocols over the same collective-noise channel. The receiver simply performs two Bell measurements to obtain the raw key. Moreover, the proposed protocols are free from several well-known attacks and can also be secure over a lossy channel.     

Two authenticated quantum dialogue protocols based on three-particle entangled states

In this paper, we propose two authenticated quantum dialogue protocols based on three-particle entangled states, which are both completely secure and more efficient. The first controlled quantum dialogue protocol with authentication is creatively proposed, which is secure under not only some famous external attacks but also internal attacks, for example, the dishonest controller’s attack. This protocol has a slightly increasing efficiency and less qubit cost compared to previous protocols. Besides, we present the second authenticated quantum dialogue protocol, which has a high efficiency with 80% by integrating dense coding. This protocol can also resist various well-known attacks.     

Controlled quantum dialogue using cluster states

This paper presents a new controlled quantum dialogue (CQD) protocol based on the cluster entangled states. The security analyses indicate that the proposed scheme is secure under not only various well-known attacks but also the collusive attack, where the participants may collude to communicate without the controller’s permission. Compared to a previous CQD scheme, which is also robust against the conspiracy attack, the proposed protocol is more efficient in both the qubit efficiency and the hardware requirement.     

基于高维纠缠交换的无酉操作确定性安全量子通信

在分析高维Bell态纠缠交换基本性质的基础上,提出不需要任何酉操作、具有通用性和一般性的高维确定性安全量子通信方案.利用高维Bell测量的结果,发送方和接收方分别进行模加、减运算即可编码、解码信息.构造了两组互补的基,并根据其互补性质,提出了检测高维量子信道是否安全的方法.详细分析了几种常用攻击策略,并计算了这些攻击所引起的错误率,进而推导出通信双方需设定的错误率阈值的上界.     

Deterministic secure quantum communication without unitary operation based on high-dimensional entanglement swapping

By analysis of the basic properties of entanglement swapping of high-dimensional Bell states,a universal and general deterministic secure quantum communication(DSQC)protocol is proposed,in which unitary operation is not required.By making use of the results of high-dimensional Bell measurement,the sender and the receiver can encode and decode the message respectively by performing the modular addition and subtraction.Two mutually complementary bases are constructed;and according to the property of mutual complement,a method for checking security of the high-dimensional quantum channel is put forward.Some common attack strategies are analyzed,and the corresponding error rates are calculated.Then the upper bound of the threshold of error rate is deduced.     

Relativistic entanglement in single-particle quantum states using non-linear entanglement witnesses

In this study, the spin-momentum correlation of one massive spin- ${\frac{1}{2}}$ and spin-1 particle states, which are made based on the projection of a relativistic spin operator into timelike direction is investigated. It is shown that by using Non-Linear entanglement witnesses (NLEWs), the effect of Lorentz transformation would decrease both the amount and the region of entanglement.     

Protection of quantum Fisher information in entangled states via classical driving

Quantum entanglement can offer a quadratic enhancement in the precision of parameter estimation. We here study the protection of quantum Fisher information (QFI) of the phase parameter in entangled-atom states within the framework of independently dissipative environments and driven individually by classical fields. It is shown that the QFI of the phase parameter can be protected effectively only when the classical fields that drive all atoms are suitably strong, and if one of them vanishes or is very weak, then the ability of protection loses, no matter how strong the other driving fields are. We also study the evolution of fidelity of the entangled state itself and find that though the protections of QFI and quantum states are two different notions, the method can also be used to protect quantum states effectively when the driving fields are suitably strong.     

Efficient deterministic secure quantum communication protocols using multipartite entangled states

We propose two deterministic secure quantum communication protocols employing three-qubit GHZ-like states and five-qubit Brown states as quantum channels for secure transmission of information in units of two bits and three bits using multipartite teleportation schemes developed here. In these schemes, the sender’s capability in selecting quantum channels and the measuring bases leads to improved qubit efficiency of the protocols.     

基于Bell态纠缠交换的身份认证协议

提出了一种新的量子身份认证协议,该协议以Bell态为传输载体,利用Bell态纠缠交换和Bell基测量对通信用户进行身份认证。两个Bell态的传送过程中不需要做任何的幺正变换,只需要执行Bell基测量和按位异或运算就可以实现信息的传输。整个过程中,量子载体操作简单且容易实现。此外,也验证了此协议的正确性。     

A new method for quantifying entanglement of multipartite entangled states

We propose a new way for quantifying entanglement of multipartite entangled states which have a symmetrical structure and can be expressed as valence-bond-solid states. We put forward a new concept ‘unit.’ The entangled state can be decomposed into a series of units or be reconstructed by multiplying the units successively, which simplifies the analyses of multipartite entanglement greatly. We compute and add up the generalized concurrence of each unit to quantify the entanglement of the whole state. We verify that the new method coincides with concurrence for two-partite pure states. We prove that the new method is a good entanglement measure obeying the three necessary conditions for all good entanglement quantification methods. Based on the method, we compute the entanglement of multipartite GHZ, cluster and AKLT states.     

Generation of entangled coherent-squeezed states: their entanglement and nonclassical properties

In this paper, after a brief review on the coherent states and squeezed states, we introduce two classes of entangled coherent-squeezed states. Next, in order to generate the introduced entangled states, we present a theoretical scheme based on the resonant atom-field interaction. In the proposed model, a \(\varLambda \)-type three-level atom interacts with a two-mode quantized field in the presence of two strong classical fields. Then, we study the amount of entanglement of the generated entangled states using the concurrence and linear entropy. Moreover, we evaluate a few of their nonclassical properties such as photon statistics, second-order correlation function, and quadrature squeezing and establish their nonclassicality features.     

Cryptanalysis and improvement on two efficient remote user authentication scheme using smart cards

In 2002, Chien et al. proposed an efficient remote authentication scheme using smart cards, in which only few hashing operations are required. Later, Ku et al. gave an improved scheme to repair the security pitfalls found in Chien et al.'s scheme. Also Yoon et al. presented an enhancement on Ku et al.'s scheme. In this paper, we show that both Ku et al.'s scheme and Yoon et al.'s scheme are still vulnerable to the guessing attack, forgery attack and denial of service (DoS) attack. In addition, their schemes lack efficiency when users input wrong passwords. To remedy these flaws, this paper proposes an efficient improvement over Ku et al.'s and Yoon et al.'s schemes with more security. The computation cost, security, and efficiency of the improved scheme are embarking for the real application in the resource-limited environment.     

基于纠缠的量子密钥分配协议仿真

由于受物理资源和实验条件的限制,在经典计算机上对量子密钥分配（QKD）仿真,为研究者提供一种手段以便更好地掌握这类抽象协议。对以纠缠态为基础的E91协议的量子密钥分配过程进行仿真,重点对比分析了理想环境、有噪环境以及窃听环境下的仿真结果,并验证该量子密钥分配协议的安全性。     

Quantum private comparison protocol based on entanglement swapping of d-level Bell states

In this paper, we propose a quantum private comparison protocol based on entanglement swapping, where two distrustful parties can compare the values of their secrets with the help of a semi-trusted third party. The protocol can determine not only whether two secrets are equal, but also the size relationship between them. The two parties can deduce the comparison result based on the keys shared between them and the announcement of the third party. Others including the third party will learn nothing about the values of the secrets, as well as the comparison result. The security of our protocol is analyzed. Furthermore, all the particles can be reused in the same protocol model theoretically. So our protocol is efficient and feasible to expand in network service, which in turn gives a solution to the left problem in Lin et al. (Quantum Inf Process, doi:10.1007/s11128-012-0395-6, 2012).     

A quantum secure direct communication protocol using entangled modified spin coherent states

Quantum Information Processing - In this paper, a new direct quantum communication protocol based on a modified spin coherent state as decoy particles is to be depicted, before that both the scheme...     

任意二粒子纠缠态的受控量子通信

为了解决任意二量子通信问题,首先给出了五粒子和七粒子纠缠态的构造方法,并提供了它们的量子线路图。其次,以该五粒子纠缠态为量子信道,提出一个任意二粒子未知量子态的受控隐形传态协议。该协议在监察者Charlie的控制下,Alice进行四粒子投影测量和经典通信,Bob采用简单酉变换就能以100%的概率成功重构一个任意二粒子纠缠态。最后,利用七粒子纠缠态为量子信道,提出了任意二粒子纠缠态的联合受控远程制备方案。在此方案中,发送者Alice用自己掌握被制备态的部分信息构造测量基,发送者Bob采用前馈测量策略,接收者Diana在监控者Charlie的帮助下,通过简单幺正变换就能确定性地恢复原始态。     

Secure quantum report with authentication based on six-particle cluster state and entanglement swapping

A novel high-efficient secure quantum report with authentication based on six-particle cluster state and entanglement swapping is proposed.In our protocol,using N groups of six-particle cluster state,the legitimate users Bob and Charlie send their secret reports to their boss(Alice),who operates sixteen kinds of unitary operations after receiving the reports.Here,entanglement swapping of cluster states and maximum entanglement state measurement are employed by the communicators.It has been proved that our protocol has high level guarantees and honesty,and the scheme is secure not only against the intercept-and-resend attack but also against disturbance attack.