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We propose an authenticated quantum dialogue protocol, which is based on a shared private quantum entangled channel. In this protocol, the EPR pairs are randomly prepared in one of the four Bell states for communication. By performing four Pauli operations on the shared EPR pairs to encode their shared authentication key and secret message, two legitimate users can implement mutual identity authentication and quantum dialogue without the help from the third party authenticator. Furthermore, due to the EPR pairs which are used for secure communication are utilized to implement authentication and the whole authentication process is included in the direct secure communication process, it does not require additional particles to realize authentication in this protocol. The updated authentication key provides the counterparts with a new authentication key for the next authentication and direct communication. Compared with other secure communication with authentication protocols, this one is more secure and efficient owing to the combination of authentication and direct communication. Security analysis shows that it is secure against the eavesdropping attack, the impersonation attack and the man-in-the-middle (MITM) attack. [ABSTRACT FROM AUTHOR]

Recently, Hwang et al. (Eur. Phys. J. D 61:785, ) and Yuan et al. (Int. J. Theor. Phys. 50:2403, ) have proposed two efficient protocols of secure quantum communication using 3-qubit and 4-qubit symmetric W state respectively. These two dense coding based protocols are generalized and their efficiencies are considerably improved. Simple bounds on the qubit efficiency of deterministic secure quantum communication (DSQC) and quantum secure direct communication (QSDC) protocols are obtained and it is shown that dense coding is not essential for designing of maximally efficient DSQC and QSDC protocols. This fact is used to design maximally efficient protocols of DSQC and QSDC using 3-qubit and 4-qubit W states. [ABSTRACT FROM AUTHOR]

A quantum secure direct communication protocol with authentication using only two nonorthogonal states is presented. In the protocol, a one-way hash function is utilized for two-way authentication and two one-particle unitary operations are used for encoding. Moreover, it has been shown that this protocol is secure against some common attacks. [ABSTRACT FROM AUTHOR]

A novel quantum secure direct communication scheme based on four-qubit cluster states is proposed. In this scheme, the quantum channel between the sender Alice and the receiver Bob consists of an ordered sequence of cluster states which are prepared by Alice. After ensuring the security of quantum channel, Alice prepares the encoded Bell-state sequence, and performs Bell-basis measurements on the qubits at hand. Then Alice tells the measured results to Bob, and Bob also performs Bell-basis measurements on his own qubits. Finally Bob can get the secret information through the analysis of their measured results. In our scheme, the qubits carrying the secret message do not need to be transmitted in public channel. We show this scheme is determinate and secure. [ABSTRACT FROM AUTHOR]

We propose an efficient scheme for generation of three-atom singlet state in a bimodal cavity based on quantum Zeno dynamics and the large detuning condition. The influence of decoherence induced by cavity decay and atomic spontaneous emission is also discussed by numerical calculation. The advantages of the scheme are that the initial input states of atoms are not entangled and the fidelity is insensitive to cavity decay and atomic spontaneous emission due to no exciting the cavity fields during the whole evolution and the large detuning condition. [ABSTRACT FROM AUTHOR]

In this paper, a quantum private comparison protocol with Bell states is proposed. In the protocol, two participants can determine the relationship between their secret inputs in size, with the assistance of a semi-trusted third party. The presented protocol can ensure fairness, correctness, and security. Meanwhile, all the particles undergo only a one-way trip, which improves the efficiency and security of the communication. Furthermore, only Bell states are exploited in the implementation of the protocol, and two participants are just required having the ability to perform single particle operations, which make the presented protocol more feasible in technique. [ABSTRACT FROM AUTHOR]

Recently, Ge and Liu (Chin. Phys. Lett. 24(10):2727-2729, ) proposed a quantum secure direct communication (QSDC) protocol using a decoherence-free subspace (DFS) against collective-dephasing noise. Users of their protocol can directly recover the secret message after quantum transmission without transmission of any additional classical information except for the eavesdropping check. This study points out a pitfall in Ge and Liu's scheme, in which an eavesdropper can deliberately modify the message without being detected. Furthermore, an enhanced scheme is proposed to avoid the modification attack and to improve the qubit efficiency from 8.3 % to 12.5 %. [ABSTRACT FROM AUTHOR]

In this paper, we propose a protocol for teleporting the photon polarization-entangled state from a sender to a receiver in terms of optical elements. We show that the quantum teleportation protocol can be successfully realized with a certain probability by using a W state as the quantum channel. This protocol is based on optical elements, which are feasible with existing experimental technology. [ABSTRACT FROM AUTHOR]

We presents a novel scheme for high-capacity three-party quantum secret sharing (QSS) with the hyperentanglement in both the polarization and the spatial-mode degrees of freedom of photon pairs. The boss Alice need only prepare a sequence of photon pairs and some decoy photons. Her two agents measure their photons received from the boss Alice with two bases by choosing two unsymmetrical probabilities. The present QSS scheme has a high capacity as each pair can carry 2 bits of information, several times as other QSS schemes. Moreover, our setups with linear optical elements show that our QSS scheme does not increase the difficulty of its implementation in experiment and it is feasible with current techniques. [ABSTRACT FROM AUTHOR]

Two novel single-photon deterministic secure quantum communication (DSQC) schemes with collective detection are proposed. One is a two-party DSQC, the other is a DSQC network. In these two schemes, only single-photon source and single-photon measurements are required, which makes the schemes more feasible with present techniques. Apart from this, a detection strategy called collective detection is utilized in our schemes, in which the detection is taken only once after the whole process of particle transmission. Such detection strategy improves the efficiencies of our protocols and also reduces the cost of realization as the message sender only need to perform unitary operations in the whole communication. What's more, the efficiencies of qubits and source capacity are both high since almost all the states can be used to transmit message except the ones used for eavesdropping check and each single photon can carry one bit of information. Finally, we prove the security of the our protocols by using the theorems on quantum operation discrimination. [ABSTRACT FROM AUTHOR]

We propose a novel entanglement concentration protocol (ECP) for nonlocal N-photon systems in a partially entangled pure W-class state, following some ideas in the work by Deng (Phys. Rev. A 85:022311, ). Our ECP resorts to an ancillary single photon and the projection measurement on it. Compared with other ECPs for W-class states, our ECP requires only one copy of the multipartite entangled system in a partially entangled W-class pure state, not two copies, which reduces the difficulty of its implementation largely. Moreover, it requires only one of the N parties in quantum communication to perform the local unitary operation for reconstructing the standard W state from the W-class state and it only resorts to linear optical elements for its implementation. All these advantages make our ECP more feasible than others in practical applications in quantum communication. [ABSTRACT FROM AUTHOR]

In this work we show that the generating N-photon Greenberger-Horne-Zeilinger entangled state protocol proposed by Xia et al. (Appl Phys Lett 92(1-3):021127, ) which can be realized by a simpler optical setup and with a higher success probability. The present protocol setup involves simple linear optical elements, N single-photon superposition states and conventional photon detectors. This makes the protocol more realizable in experiments. [ABSTRACT FROM AUTHOR]

Based on the genuine four-particle entangled state (Yeo and Chua in Phys. Rev. Lett. 96:060502, ) and the ping-pong protocol (Boström and Felbinger in Phys. Rev. Lett. 89:187902, ), an efficient quantum dialogue scheme is proposed. Since some subtle methods are employed, the information leakage doesn't exist in this scheme. There are two security-check processes in this scheme, one is accomplished by using the four-particle entanglement pairs and the other by using the d particles. [ABSTRACT FROM AUTHOR]

We propose explicit quantum circuits for implementing a positive operator valued measurement (POVM), by which a class of relatively general entanglement conversion can be realized determinately. Different from conventional method based on decomposition of unitary matrices, our implementation procedure involves decomposition of the evolution process from the initial state to the final state with quantum Toffoli gates. [ABSTRACT FROM AUTHOR]

We propose two schemes for quantum state sharing of single-qubit state by using three-qutrit and three-qudit entangled states as quantum channel, respectively. After the sender performs a non-symmetric basis measurement on her particles, and the controller operates a single-particle measurement on his particle, the state receiver can reconstruct the original state of the sender by applying the appropriate unitary operation. The analysis of the security in the schemes has been given. [ABSTRACT FROM AUTHOR]

novel high-capacity protocol for deterministic secure quantum communication with four-qubit symmetric W state is proposed. In the presented protocol, the secret messages can be encoded on the four-qubit symmetric W states by employing four two-particle unitary operations and directly decoded by utilizing the corresponding measurements in Bell basis or single particle basis. It has a high capacity as each W state can carry two bits of secret information, and has a high intrinsic efficiency because almost all the instances are useful. The security of this communication can be ensured by the decoy photon checking technique and the order rearrangement of particle pairs technique. Furthermore, this protocol is feasible with present-day technique. [ABSTRACT FROM AUTHOR]

The non-coherent attack on the ping-pong protocol with completely entangled pairs of three-dimensional quantum systems (qutrits) is analyzed. The expression for the amount of the eavesdropper's information as functions of attack detection probability is derived. It is shown that the security of the ping-pong protocol with pairs of qutrits is higher than the security of the protocol with pairs of qubits. It is also shown that with the use by legitimate users in a control mode of two mutually unbiased measuring bases, the ping-pong protocol with pairs of qutrits possesses only asymptotic security, as well as the protocol with entangled qubits. [ABSTRACT FROM AUTHOR]

We propose a linear optical protocol to generate Greenberger-Horne-Zeilinger (GHZ) state under control of a number of controllers in terms of optical elements. The proposed setup involves simple linear optical elements, ( N−1)-photon polarization entangled state, and conventional photon detectors. We show that the protocol can be successfully realized with a certain probability. [ABSTRACT FROM AUTHOR]

We investigate the influence of Kerr medium on atomic population probability and residual entanglement of the system which consists of cascade-type three-level atoms and a bimodal cavity field filled with Kerr medium. The results show that the period of residual entanglement is shortened and the value of residual entanglement is enhanced by appropriately adjusting the nonlinear Kerr constant. Furthermore, we also study the influence of Kerr medium on entanglement evolution of the two atoms, and find that it decreases the value of entanglement between two atoms. [ABSTRACT FROM AUTHOR]

A scheme for concentrating entanglement in two partially entangled Einstein-Podolsky-Rosen (EPR) pairs using repetitious resonant interactions of the atoms with a single-mode cavity field is proposed. A maximally entangled EPR pair can be deterministically extracted with the success probability of 1.0. In the scheme, the two logical states of a qubit are represented by the two lowest levels of an atom while a higher-energy intermediate level is used to facilitate the realization of the unitary operations, and all the operations required to realize deterministic entanglement concentration can be implemented in a reasonable amount of time before decoherence sets in. The scheme might be experimentally realizable with presently available cavity QED techniques and gives a realistic means to realize entanglement concentration deterministically. [ABSTRACT FROM AUTHOR]

We propose a quantum secure direct communication scheme based on non-orthogonal entangled pairs and local measurement. In this scheme, we use eight non-orthogonal entangled pairs to act as quantum channels. Due to the non-orthogonality of the quantum channels, the present protocol can availably prohibit from all kinds of valid eavesdropping and acquire a secure quantum channel. By local measurement, the sender acquires a secret random sequence. The process of encoding on the random sequence is identical to the one in one-time-pad. So the present protocol is secure. Even for a highly lossy channel, our scheme is also valid. The scheme is feasible with present-day techniques. [ABSTRACT FROM AUTHOR]

In this paper, a new set of functions called fractional-order Euler functions (FEFs) is constructed to obtain the solution of fractional integro-differential equations. The properties of the fractional-order Euler functions are utilized to construct the operational matrix of fractional integration. By using the matrix and the functions approximation, the fractional integro-differential equations are reduced to systems of algebraic equations. The convergence analysis of fractional-order Euler functions approximation is given. Illustrative examples are included to demonstrate the high precision and good performance of the new scheme. [ABSTRACT FROM AUTHOR]