Controlled Quantum Secure Direct Communication by?Using Four Particle Cluster States

We present a controlled quantum secure direct communication protocol by using cluster states via swapping quantum entanglement and local unitary operation. In the present scheme, the sender transmit the secret message to the receiver directly and the secret message can only be recovered by the receiver under the permission of the controller.     

Quantum state sharing of an arbitrary m-qudit state with two-qudit entanglements and generalized Bell-state measurements

A scheme for quantum state sharing of an arbitrary m-qudit state is proposed with two-qudit entanglements and generalized Bell-state (GBS) measurements. In this scheme, the sender Alice should perform m two-particle GBS measurements on her 2m qudits, and the controllers also take GBS measurements on their qudits and transfer their quantum information to the receiver with entanglement swapping if the agents cooperate. We discuss two topological structures for this quantum state sharing scheme, a dispersive one and a circular one. The former is better at the aspect of security than the latter as it requires the number of the agents who should cooperate for recovering the quantum secret larger than the other one.     

Large-capability quantum key distribution with entangled qutrits

A secure quantum key distribution protocol is proposed to distribute the three-dimensional secret message in a two-way quantum channel based on the entanglement of two-qutrit quantum system. The present protocol has an advantage over transmitting directly the secret message with large capacity since the distributed message has been imposed on nonorthogonal two-qutrit-entangled states by the sender using the superdense coding via local unitary operations. The security is ensured by the entanglement of the two-qutrit quantum system and the secure transmission of the traveling-particle sequence in the lossless and noiseless channel.     

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.     

Multiparty Quantum Secret Sharing of Quantum States Using Entanglement States

A multi-partite-controlled quantum secret sharing scheme using several non-orthogonal entanglement states is presented with unconditional security. In this scheme, the participants share the secret quantum state by exchanging the secret polarization angles of the disordered travel particles. The security of the secret quantum state is also guaranteed by the non-orthogonal multi-partite-controlled entanglement states, the participants＇ secret polarizations, and the disorder of the travelling particles. Moreover, the present scheme is secure against the particle-number splitting attack and the intercept-and-resend attack. It may be still secure even if the distributed quantum state is embedded in a not-so-weak coherent-state pulse.     

Generalized quantum state sharing of the arbitrary two particles state

This paper has proposed a generalized quantum state sharing protocol of an arbitrary two-particle state using non-maximally GHZ states and generalized Bell state measurement.The sender Alice performs two-particle generalized Bell state measurements on her two particles in the state sharing process and the controller takes measurements on his particles and transfers the quantum information to the receiver with entanglement swapping by the cooperation of the other agents.It is found that the use of nonmaximally entangled state in quantum state sharing has enabled the secure sharing of the quantum state.     

一种基于纠缠态的量子中继通信系统

提出了一种基于纠缠态的量子中继通信系统,该系统应用纠缠为基本资源.纠缠为量子隐形传态和绝对安全的量子通信提供了保证.量子中继器用来延长高纠缠度的纠缠光子对的纠缠距离,利用纠缠交换和纠缠纯化在系统的发信者与受信者之间建立光子对的纠缠.应用量子隐形传态的原理传输量子信息.系统分析表明,量子通信系统的吞吐率随着通信双方成功建立纠缠的概率增大而显著增加,量子信号的传输距离取决于量子中继节点的级数.     

基于纠缠交换和团簇态实现二粒子任意态的可控隐形传态

提出一个对二粒子任意态的可控隐形传态方案,利用四粒子团簇态作为量子信道,用EPR态实现控制.首先,发送者向控制者提出申请,控制者再对其拥有的2个粒子做Bell基测量,并把结果通知发送者,实现纠缠交换.然后,发送者对自己手中的四个粒子做适当的幺正变换,接着进行纽曼测量,并把结果通知接受者.接受者根据发送者的测量结果,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二粒子任意态.方案成功的概率为100%.     

Quantum key distribution by comparing Bell states

We propose a quantum key distribution (QKD) scheme based on entanglement swapping. In this scheme, the methods to form secret keys are so interesting. By comparing initial Bell state and outcome of entanglement swapping, the secret keys between Alice and Bob are generated involuntarily.     

Controlled deterministic secure quantum communication using five-qubit entangled states and two-step security test

A five-qubit entangled state is constructed with the four-qubit genuine entangled state. As one of its applications, a controlled deterministic secure quantum communication scheme is proposed. Firstly, the supervisor prepares the five-qubit entangled state and distributes uniformly the four qubits to two users and keeps the rest one for control function. Then the receiver can perform jointly projective measurement on the encoded qubits from the sender to decrypt the secret information. The two-step security test ensures the security of the communication. Moreover, quantum dense coding is applied to enhance the capacity of quantum channel. The communication is realized under the control of the supervisor.     

Quantum Secure Direct Communication Using Six-Particle Maximally Entangled States and Teleportation

The sender shares six-particle maximally entangled states as quantum channel with the receiver. If the quantum channel is secure, the sender performs projective measurements and tells the measurement outcome to the receiver. The receiver performs the unitary transformations and makes projective measurements on his particles to obtain the secret information. Using teleportation, the transmission of three-qubit secret information can be completed in each quantum channel     

Quantum secure direct communication by entangled qutrits and entanglement swapping

A protocol for quantum secure direct communication by using entangled qutrits and swapping quantum entanglement is proposed. In this protocol, a set of ordered two-qutrit entangled states is used as quantum information channels for sending secret messages directly. During the process of transmission of particles, the transmitted particles do not carry any secret messages and are transmitted only one time. The protocol has higher source capacity than protocols using usual two-dimensional Bell-basis states as quantum channel. The security is ensured by the unitary operations randomly performed on all checking groups before the particle sequence is transmitted and the application of entanglement swapping.     

Controlled Secure Direct Communication with Seven-Qubit Entangled States

In this paper, a new controlled secure direct communication protocol based on a maximally seven-qubit entangled state is proposed. the outcomes of measurement is performed by the sender and the controller, the receiver can obtain different secret messages in a deterministic way with unit successful probability.In this scheme,by using entanglement swapping, no qubits carrying secret messages are transmitted.Therefore, the protocol is completely secure.     

Cryptanalysis and improvement of a DSQC using four-particle entangled state and entanglement swapping

The security of a deterministic secure quantum communication using four-particle genuine entangled state and entanglement swapping [X.M. Xiu, H.K. Dong, L. Dong, Y.J. Cao, F. Chi, Opt. Commun. 282 (2009) 2457] is analyzed. It is shown that an eavesdropper can entangle an ancilla without introducing any error in the security test utilizing a speciality of the four-particle genuine entangled state. Moreover, the eavesdropper can distill a quarter of the secret information from her entangled ancilla. Finally, a simple improvement to resist this attack is proposed.     

A Cooperative Quantum Anonymous Transmission with Hybrid Entanglement Swapping

Motivated by hybrid entanglement swapping, a cooperative protocol for quantum anonymous transmission is proposed. In the protocol, three pairs of hybrid-entangled photons are deployed in the small-scale quantum network, where a photon is traveling from one random participant to another. After performing by entanglement swapping among all participants, the anonymous transmission system is established in a cooperative way. Analysis shows that the proposed scheme achieves the secure anonymity for both sender and receiver. In addition, it can transmit quantum message with high efficiency.     

Efficient high-capacity quantum secret sharing with two-photon entanglement

An efficient high-capacity quantum secret sharing scheme is proposed following some ideas in quantum dense coding with two-photon entanglement. The message sender, Alice prepares and measures the two-photon entangled states, and the two agents, Bob and Charlie code their information on their photons with four local unitary operations, which makes this scheme more convenient for the agents than others. This scheme has a high intrinsic efficiency for qubits and a high capacity.     

Quantum Key Distribution against Trojan Horse Attacks

Realistic experimental apparatus of quantum cryptography are imperfect, which may be utilized by a potential eavesdropper to eavesdrop on the communication. We show that quantum communication may be improved with quantum teleportation and entanglement swapping, which is robustly secure against the most general Trojan horse attacks. Our scheme is not an improvement of the communication apparatus, but the improvement of quantum communication protocol itself. We show that our modified schemes may be implemented with current technology.     

量子比特的普适远程翻转和克隆

提出一种把量子隐形传态、最佳普适量子比特翻转和最佳普适量子克隆三者结合起来的量子比特普适远程翻转和克隆方案.当发送者和处于不同地点的三个接收者共享一个特定的四粒子纠缠态作为量子信道时,通过发送者的Bell基测量、经典通信和各个接收者的局域幺正变换,一个接收者能够以2/3的最佳保真度得到一份原未知量子比特的正交补态,另外两个接收者能够分别以5/6的最佳保真度得到原未知量子比特的一份拷贝.此方案用较少的量子纠缠资源同时完成了未知量子比特的普适远程翻转和克隆,且其保真度分别达到了最佳.实现此方案的关键在于构造出发送者和接收者共享的特定四粒子纠缠态作为量子信道,分析了此特殊四粒子态内在的纠缠结构.     

Controlled quantum secure direct communication using a non-symmetric quantum channel with quantum superdense coding

We present a controlled quantum secure direct communication protocol that uses a 2-dimensional Greenberger–Horne–Zeilinger (GHZ) entangled state and a 3-dimensional Bell-basis state and employs the high-dimensional quantum superdense coding, local collective unitary operations and entanglement swapping. The proposed protocol is secure and of high source capacity. It can effectively protect the communication against a destroying-travel-qubit-type attack. With this protocol, the information transmission is greatly increased. This protocol can also be modified, so that it can be used in a multi-party control system.     

Multiparty controlled quantum secure direct communication using Greenberger-Horne-Zeilinger state

Based on the idea of dense coding of three-photon entangled state and qubit transmission in blocks, we present a multiparty controlled quantum secret direct communication scheme by using Greenberger-Horne-Zeilinger state. In the present scheme, the sender transmits three bits of secret message to the receiver directly and the secret message can only be recovered by the receiver under the permission of all the controllers. All three-photon entangled states are used to transmit the secret message except those chosen for eavesdropping check and the present scheme has a high source capacity because Greenberger-Horne-Zeilinger state forms a large Hilbert space.