Selective Atom-Cavity Interaction Scheme for Quantum Controlled-NOT Gate Using Four-Level Atoms in Cavity QED System

We propose a scheme for realization a quantum Controlled-NOT gate operation using two four-level atoms through a selective atom cavity interaction in cavity quantum electrodynamics system. In our protocol, the quantum information is encoded on the stable ground states of the two atoms. During the interaction between atoms and single-mode vacuum cavity-field, the atomic spontaneous emission is negligible as the large atom-cavity detuning effectively suppresses the spontaneous decay of the atoms. The influences of the dissipation and the deviation of interaction time on fidelity and corresponding success probability of the quantum Controlled-NOT gate and the experimental feasibility of our proposal are also discussed.     

Secure Quantum Dialogue Protocol Based On Four-Qubit Cluster State

In this paper, a quantum dialogue protocol is proposed based on four-qubit Cluster state, which constructed a new quantum channel. By using Bell measurements and the corresponding unitary operation, two users can exchange their messages simultaneously and directly. And two security cheques are adopted to ensure its transmission security against the several well-known attacks from an outside eavesdropper. The protocol can avoid the information leakage, and it is simple and feasible with current technique.     

Quantum Dialogue Without Information Leakage Using a Single Quantum Entangled State

At present, a lot of quantum dialogue protocols have the problem of information leakage, especially the ones merely using a single quantum state as the quantum resource. In this paper, the author successfully puts forward a novel kind of information leakage resistant quantum dialogue protocol merely using a single quantum entangled state. This kind of quantum dialogue protocol uses the measurement correlation property of a single quantum entangled state to prevent the information leakage problem. Its Bell state version is illustrated in detail at first in this paper, then it is generalized to the cases of three-particle, four-particle and five-particle quantum entangled states. Different from those previous information leakage resistant quantum dialogue protocols, the proposed protocol needs neither the auxiliary quantum state nor the entanglement swapping technology of quantum state.     

Quantum Secure Dialogue with Quantum Encryption

How to solve the information leakage problem has become the research focus of quantum dialogue. In this paper, in order to overcome the information leakage problem in quantum dialogue, a novel approach for sharing the initial quantum state privately between communicators, i.e., quantum encryption sharing, is proposed by utilizing the idea of quantum encryption. The proposed protocol uses EPR pairs as the private quantum key to encrypt and decrypt the traveling photons, which can be repeatedly used after rotation. Due to quantum encryption sharing, the public announcement on the state of the initial quantum state is omitted, thus the information leakage problem is overcome.The information-theoretical efficiency of the proposed protocol is nearly 100%, much higher than previous information leakage resistant quantum dialogue protocols. Moreover, the proposed protocol only needs single-photon measurements and nearly uses single photons as quantum resource so that it is convenient to implement in practice.     

Quantum Secure Dialogue with Quantum Encryption

How to solve the information leakage problem has become the research focus of quantum dialogue. In this paper, in order to overcome the information leakage problem in quantum dialogue, a novel approach for sharing the initial quantum state privately between communicators, i.e., quantum encryption sharing, is proposed by utilizing the idea of quantum encryption. The proposed protocol uses EPR pairs as the private quantum key to encrypt and decrypt the traveling photons, which can be repeatedly used after rotation. Due to quantum encryption sharing, the public announcement on the state of the initial quantum state is omitted, thus the information leakage problem is overcome. The information-theoretical efficiency of the proposed protocol is nearly 100%, much higher than previous information leakage resistant quantum dialogue protocols. Moreover, the proposed protocol only needs single-photon measurements and nearly uses single photons as quantum resource so that it is convenient to implement in practice.     

Quantum Logic Gates and Cluster States with Four-level Atoms in Cavity QED

We propose a model to implement the two-qubit quantum logic gates, i.e., the quantum phase gate and the Controlled-NOT gate, and generate the atomic qubits cluster states with a large detuned interaction between four-level atoms and a single-mode cavity field. In the presented protocol, the quantum information is encoded on the stable ground states of the atoms, and the effect of decoherence from atomic spontaneous emission is negligible. In addition, the interaction between atoms and the cavity is large detuned, and the cavity is only virtually excited. Therefore, the scheme is insensitive to the cavity decay. The experimental feasibility of our proposal is also discussed.     

Secure Quantum Dialogue Protocol Based on W States Without Information Leakage

A quantum dialogue protocol is proposed based on triple particle W states. Each particle is transferred only once in the entire communication, which reduces the risk of eavesdropping and improves the security of the protocol. The protocol can resist various attacks. The efficiency of this protocol can be up to 80 % without information leakage.     

Efficient Three-Party Quantum Dialogue Protocol Based on the Continuous Variable GHZ States

Based on the continuous variable GHZ entangled states, an efficient three-party quantum dialogue protocol is devised, where each legitimate communication party could simultaneously deduce the secret information of the other two parties with perfect efficiency. The security is guaranteed by the correlation of the continuous variable GHZ entangled states and the randomly selected decoy states. Furthermore, the three-party quantum dialogue protocol is directly generalized to an N-party quantum dialogue protocol by using the n-tuple continuous variable GHZ entangled states.     

Efficient quantum private comparison protocol utilizing single photons and rotational encryption

As a branch of quantum secure multiparty computation, quantum private comparison is applied frequently in many fields, such as secret elections, private voting, and identification. A quantum private comparison protocol with higher efficiency and easier implementation is proposed in this paper. The private secrets are encoded as single polarized photons and then encrypted with a homomorphic rotational encryption method. Relying on this method and the circular transmission mode, we implement the multiplexing of photons, raising the efficiency of our protocol to 100%. Our protocol is easy to realize since only single photons, unitary operation, and single-particle measurement are introduced. Meanwhile, the analysis shows that our protocol is also correct and secure.     

Semi-quantum Dialogue Based on Single Photons

In this paper, we propose two semi-quantum dialogue (SQD) protocols by using single photons as the quantum carriers, where one requires the classical party to possess the measurement capability and the other does not have this requirement. The security toward active attacks from an outside Eve in the first SQD protocol is guaranteed by the complete robustness of present semi-quantum key distribution (SQKD) protocols, the classical one-time pad encryption, the classical party’s randomization operation and the decoy photon technology. The information leakage problem of the first SQD protocol is overcome by the classical party’ classical basis measurements on the single photons carrying messages which makes him share their initial states with the quantum party. The security toward active attacks from Eve in the second SQD protocol is guaranteed by the classical party’s randomization operation, the complete robustness of present SQKD protocol and the classical one-time pad encryption. The information leakage problem of the second SQD protocol is overcome by the quantum party’ classical basis measurements on each two adjacent single photons carrying messages which makes her share their initial states with the classical party. Compared with the traditional information leakage resistant QD protocols, the advantage of the proposed SQD protocols lies in that they only require one party to have quantum capabilities. Compared with the existing SQD protocol, the advantage of the proposed SQD protocols lies in that they only employ single photons rather than two-photon entangled states as the quantum carriers. The proposed SQD protocols can be implemented with present quantum technologies.     

Analyzing and Revising Quantum Dialogue Without Information Leakage Based on the Entanglement Swapping Between any Two Bell States and the Shared Secret Bell State

Information leakage in quantum dialogue (QD) or bidirectional quantum secure direct communication (BQSDC) was found ten years ago, but enough attention was not paid and even wrong conclusions were drawn. It is indeed necessary to emphasize the importance. Here, we find information leakage exists in the QD protocol based on entanglement swapping between any two Bell states and the shared secret Bell state. To be specific, half of the interchanged information is leaked out unconsciously. This is not allowed in a truly secure QD protocol. Afterward, this QD protocol is improved to the one without information leakage. Compared with the original one, there are some obvious advantages in the improved version.

     

Eavesdropping on the quantum dialogue protocol in lossy channel

We present an improved eavesdropping scheme on the quantum dialogue protocol in lossy channel,which is based on the strategies of W’ojcik [Phys.Rev.Lett.90 157901 (2003)] and ZML [Phys.Lett.A 333 46 (2004)] attack schemes.We show that our attack scheme doubles the domain of Eve’s eavesdropping and Eve can gain more information of the communication with less risk of being detected.Finally,a possible improvement for the dialogue protocol security is proposed.     

集体噪声信道上带身份认证的无信息泄露的量子对话协议

在集体噪声条件下提出三个带身份认证的量子对话协议,两个量子对话协议分别用于抵抗集体消相干噪声和集体旋转噪声,另一个用于同时抵抗这两种集体噪声.通信双方通过广义幺正变换将自己的秘密信息编码到量子态中;并根据自己的秘密信息和携带秘密信息的粒子的初末两量子态,便可推知对方的秘密信息实现量子对话.协议的效率、安全性和无信息泄露等性能分析表明了协议的有效性.     

基于非对称量子通道受控QOT量子投票协议

提出一种量子投票协议, 协议基于非对称量子通道受控量子局域幺正操作隐形传输(quantum operation teleportation, QOT). 由公正机构CA提供的零知识证明的量子身份认证, 保证选民身份认证的匿名性. 计票机构Bob制造高维Greenberger-Horne-Zeilinger 纠缠态建立一个高维量子通信信道. 选民对低维的量子选票进行局域幺正操作的量子投票, 是通过非对称基的测量和监票机构Charlie的辅助测量隐形传输的. Bob在Charlie帮助下可以通过幺正操作结果得到投票结果. 与其他一般的QOT量子投票协议相比, 该协议利用量子信息与传输的量子信道不同维, 使单粒子信息不能被窃取、防止伪造.选举过程由于有Charlie的监督, 使得投票公正和不可抵赖.由于量子局域幺正操作隐形传输的成功概率是1, 使量子投票的可靠性得以保证. 关键词： 量子投票 高维GHZ纠缠态 非对称基测量 量子操作隐形传输     

Information Leakage in Quantum Dialogue by Using Non-Symmetric Quantum Channel

In this paper [Commun. Theor. Phys. 53(2010) 648], Zhan et al. proposed a quantum dialogue protocol by using non-symmetric quantum channel. We study the security of the protocol and find that it has the drawback of information leakage. That is, Zhan et al.'s protocol is proved to be insecure by us.     

Quantum secure direct dialogue using Einstein-Podolsky-Rosen pairs

A two-step quantum secure direct dialogue protocol using Einstein-Podolsky-Rosen(EPR)pair block is proposed.In the protocol,the dialogue messages are encoded on series of qubits and sent through a quantum channel directly.The security of the protocol is assured by its connection to the two-step quantum secure direct communication protocol,which has been proved secure.This protocol has several advantages.It is a direct communication protocol that does not require a separate classical communication for the ciphertext.It has high capacity as two bits of secret messages can be transmitted by an EPR pair.As a dialogue protocol,the two parties can speak to each other either simultaneously or sequentially.     

Efficient Quantum Dialogue by Using the Two-Qutrit Entangled States Without Information Leakage

A quantum dialogue protocol, based on the two-qutrit entangled states is proposed in this paper. In this protocol, the security of communication is ensured by the secret transmitting order of qutrits. Two legitimate users can directly transmit their secret messages by generalized Bell-basis measurement and classical communication. The efficiency of our scheme is high, which can reach to 100 %. Besides, the protocol is not only feasible in practice but also can discard the drawback “information leakage” or “classical correlation”.     

Efficient and Secure Authenticated Quantum Dialogue Protocols over Collective-Noise Channels

Based on the deterministic secure quantum communication,we present a novel quantum dialogue protocol without information leakage over the collective noise channel.The logical qubits and four-qubit decoherence-free states are introduced for resisting against collective-dephasing noise,collective-rotation noise and all kinds of unitary collective noise,respectively.Compared with the existing similar protocols,the analyses on security and information-theoretical efficiency show that the proposed protocol is more secure and efficient.     

A New Secure Quantum Key Expansion Scheme

A new quantum key expansion scheme is proposed. The protocol of quantum key expansion proposed by Hwang is analyzed and the eavesdropping scheme is presented. We found that the using of the basis sequence shared by communicating parties is the weakness of the protocol. Hence we propose a ‘purification attack’ for the eavesdropper to steal partial information of the raw key and the new key between communicating parties. In view of this defect, we propose a new protocol of quantum key expansion, where the shared key is encrypted into a sequence of unitary operators which can be used securely against the presented attack.     

Bidirectional Quantum Controlled Teleportation of Three-Qubit State by Using GHZ States

In this paper, we present a scheme of bidirectional quantum controlled teleportation of three-qubit state by using GHZ states. Alice transmits an unknown three-qubit entangled state to Bob, and Bob transmit an unknown three-qubit entangled state to Alice via the control of the supervisor Charlie. In order to facilitate the implementation in the experimental environment, the preparation method of quantum channel is given. This scheme is based on that three-qubit entangled state are transformed into two-qubit entangled state and single qubit superposition state by using Toffoli Gate and Controlled-NOT operation, receivers can by introducing the appropriate unitary transformation and auxiliary particles to reconstruct the initial state. Finally, this paper is implemented a scheme of bidirectional quantum controlled teleportation of more than two qubits via the control of the supervisor Charlie.