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The quantum network is an indispensable step toward multiuser and wide-area information interchange in the course of the development of quantum technology. When designing and deploying a quantum network, availability, robustness, flexibility, and expenditure need to be considered in a balanced way. In this article, we propose a network connected through optical switches, QNUS, that requires only terminals in the number of nodes in a quantum network, which is a great saving of resources. [ABSTRACT FROM AUTHOR]

Cooperative communication is starting to attract substantial research attention in quantum information theory. However, given a specific network, it is still unknown whether quantum cooperative communication can be successfully performed. In this paper, we investigate network coding for quantum cooperative multicast (QCM) over the classic butterfly network. A very reasonable definition of QCM is first introduced. It not only perfectly focuses on the basic idea of quantum cooperative communication, but also wonderfully reflects the characteristic of classical multicast over a specific network structure. Next, we design QCM protocol for two-level systems and generalize the protocol into d-dimensional Hilbert space. It is shown that our protocols have significant advantages in terms of resource cost and compatibility with classical multicast. Besides, the success probability, which only depends on the coefficients of the initial quantum states, is carefully analyzed. In particular if the source nodes choose the quantum equatorial states, success probability can reach 1. [ABSTRACT FROM AUTHOR]

A new security protocol for quantum sealed-bid auction is proposed to resist the collusion attack from some malicious bidders. The most significant feature of this protocol is that bidders prepare their particles with secret order in post-confirmation for encoding bids. In addition, a new theorem and its proof are given based on the theory of combinatorial mathematics, which can be used as evaluation criteria for the collusion attack. It is shown that the new protocol is immune to the collusion attack and meets the demand for a secure auction. Compared with those previous protocols, the security, efficiency and availability of the proposed protocol are largely improved. [ABSTRACT FROM AUTHOR]

As a promising branch of quantum information hiding, Quantum steganography aims to transmit secret messages covertly in public quantum channels. But due to environment noise and decoherence, quantum states easily decay and change. Therefore, it is very meaningful to make a quantum information hiding protocol apply to quantum noisy channels. In this paper, we make the further research on a quantum steganography protocol for quantum noisy channels. The paper proved that the protocol can apply to transmit secret message covertly in quantum noisy channels, and explicity showed quantum steganography protocol. In the protocol, without publishing the cover data, legal receivers can extract the secret message with a certain probability, which make the protocol have a good secrecy. Moreover, our protocol owns the independent security, and can be used in general quantum communications. The communication, which happen in our protocol, do not need entangled states, so our protocol can be used without the limitation of entanglement resource. More importantly, the protocol apply to quantum noisy channels, and can be used widely in the future quantum communication. [ABSTRACT FROM AUTHOR]

In this paper, a class of protocols for quantum private comparison is investigated. The main feature is that the symmetry of quantum states is utilized. First of all, we design a new protocol for quantum private comparison via the $$\chi $$ -type state as a special example. Then, through the in-deep research and analysis on the quantum carrier, it is found that lots of quantum states with the symmetrical characteristic can be utilized to perform the protocol successfully. It is an attractive advantage in the practical application. What is more, two players are only required to be equipped with the unitary operation machines. It means that our protocols can easily be realized and have a broad scope of application. Finally, the analyses on the protocols' security, which are mainly ensured by the symmetry of quantum states and the property of the decoy state, are given in detail. [ABSTRACT FROM AUTHOR]

In this paper, a novel scheme is investigated for quantum teleportation (QT) and quantum state sharing (QSTS). The generalized seven-qubit Brown state | B7〉 is used as information carrier. Firstly, for an arbitrary single-qubit state, we perfectly present a QT protocol and three QSTS ones, which is among three participants via | B7〉. Then we make an overall comparison among three QSTS protocols and present an almost even distribution principle of particles. Secondly, for two- and three-qubit cases, based on the almost even distribution principle we design several QT and QSTS protocols. Finally, we mainly consider our scheme’s security against dishonest participant attacks. Furthermore, for an arbitrary N-qubit state, there is a conjecture that QT and QSTS can be designed by using the generalized (2 N+1)-qubit Brown state | B2N+1〉 in Eq. (3) ( N≥2) in theoretical aspects. [ABSTRACT FROM AUTHOR]

The quantum no-cloning theorem and no-deleting theorem may be the most important quantum features for quantum communications or quantum computations. In this paper, we concentrate typical properties of random quantum evolution. We obtain that universal random evolutions change the generic unknown pure states into their orthogonal states approximately. Moreover, typical random evolutions distort the von Neumann entropy with constants. These results are extended to mixed states with a stronger orthogonal preparation ability. These typical characters are very important for quantum information retrieving or various quantum tasks. [ABSTRACT FROM AUTHOR]

In this paper, we show that some special mixed quantum resource experience the same property of pure entanglement such as Bell state for quantum teleportation. It is shown that one mixed state and three bits of classical communication cost can be used to teleport one unknown qubit compared with two bits via pure resources. The schemes are easily implement with model physical techniques. Moreover, these resources are also optimal and typical for faithfully remotely prepare an arbitrary qubit, two-qubit and three-qubit states with mixed quantum resources. Our schemes are completed as same as those with pure quantum entanglement resources except only 1 bit additional classical communication cost required. The success probability is independent of the form of the mixed resources. [ABSTRACT FROM AUTHOR]

The critical merits acquired from quantum computation require running in parallel, which cannot be benefited from previous multi-level extensions and are exact our purposes. In this paper, with qutrit subsystems the general quantum computation further reduces into qutrit gates or its controlled operations. This extension plays parallizable and integrable with same construction independent of the qutrit numbers. The qutrit swapping as its basic operations for controlling can be integrated into quantum computers with present physical techniques. Our generalizations are free of elevating the system spaces, and feasible for the universal computation. [ABSTRACT FROM AUTHOR]

Quantum steganography that utilizes the quantum mechanical effect to achieve the purpose of information hiding is a popular topic of quantum information. Recently, El Allati et al. proposed a new quantum steganography using the GHZ4 state. Since all of the 8 groups of unitary transformations used in the secret message encoding rule change the GHZ4 state into 6 instead of 8 different quantum states when the global phase is not considered, we point out that a 2-bit instead of a 3-bit secret message can be encoded by one group of the given unitary transformations. To encode a 3-bit secret message by performing a group of unitary transformations on the GHZ4 state, we give another 8 groups of unitary transformations that can change the GHZ4 state into 8 different quantum states. Due to the symmetry of the GHZ4 state, all the possible 16 groups of unitary transformations change the GHZ4 state into 8 different quantum states, so the improved protocol achieves a high efficiency. [ABSTRACT FROM AUTHOR]

The main superiority of the quantum remote preparation over quantum teleportation lies the classical resource saving. This situation may be changed from the following constructions. Our purpose in this paper is to find some special differences between these two quantum tasks besides the classical resource costs. Some novel schemes show that the first one is useful to simultaneously broadcast arbitrary quantum states, while the second one cannot because of the quantum no-cloning theorem. Moreover, these broadcast schemes may be adapted to satisfying the different receivers' requirements or distributing the classical information, which are important in various quantum applications such as the quantum secret distribution or the quantum network communication. [ABSTRACT FROM AUTHOR]

The cryptanalysis about enhancement on the quantum blind signature based on two-state vector formalism is further researched. A special attack strategy is put forward. In this strategy, the dishonest signer Bob only need make two measurements in the Z-basis. It is shown that he can illegally reveal 25 % of the secret key and message of the blind signature requester. [ABSTRACT FROM AUTHOR]

In this paper, several new protocols for the controlled remote state preparation (CRSP) by using the Brown state as the quantum channel are proposed. Firstly, we propose a CRSP protocol of an arbitrary two qubit state. Then, the CRSP protocol of an arbitrary three qubit state, which has rarely been considered by the previous papers, is investigated. The coefficients of the prepared states can be not only real, but also complex. To design these protocols, some useful and general measurement bases are constructed, which can greatly reduce the restrictions for the coefficients of the prepared states. The security analysis is provided in detail. Moreover, receiver's all recovery operations are summarized into a concise formula. [ABSTRACT FROM AUTHOR]

In this paper, we make a study on how to efficiently transmit an arbitrary two-qubit pure state to remote receiver via non-maximal entangled quantum channel. As a special case, in the first section we present a controlled-joint remote state preparation scheme based on maximally entangled channel. By some local convertible projective measurement bases, two message carriers and one controller can help the receiver Charlie reconstruct the desired state with success probability p=100 %. Then, we extend it to the case of non-maximally entangled channel. Utilizing positive operator-valued measure (POVM) measurement instead of projective measurement, the controller can assist the two senders to fulfill the task. Compared with some previous schemes, our protocol will succeed with a higher probability. And success or failure will only depend on the controller's measurement outcome, but has nothing to do with two senders' measurement results. [ABSTRACT FROM AUTHOR]

In this paper, we propose one quantum signature scheme with a weak arbitrator to sign classical messages. This scheme can preserve the merits in the original arbitrated scheme with some entanglement resources, and provide a higher efficiency in transmission and reduction the complexity of implementation. The arbitrator is costless and only involved in the disagreement case. [ABSTRACT FROM AUTHOR]

In this paper, we further research the quantum private comparison protocol with the semi-honest participant, in which two parties can test the equality of their information without revealing the content to anyone. Considering both the success of protocol and the security of information, we first give a reasonable and significant description about the semi-honest model in quantum secure communications. Moreover, based on the feature of four-qubit cluster state which has the great robust against decoherence, we propose a new protocol for the quantum private comparison. Our protocol ingeniously utilizes the special symmetry of the four-qubit cluster state to enhance the efficiency of comparison. This new protocol is secure. The participants only know the result of comparison; cannot know each other's private information. TP cannot learn anything about the private information, even about the comparison result and the length of secret inputs. [ABSTRACT FROM AUTHOR]

Motivated by some previous joint remote preparation schemes, we first propose some quantum circuits and photon circuits that two senders jointly prepare an arbitrary one-qubit state to a remote receiver via GHZ state. Then, by constructing KAK decomposition of some transformation in SO(4), one quantum circuit is constructed for jointly preparing an arbitrary two-qubit state to the remote receiver. Furthermore, some deterministic schemes of jointly preparing one-qubit and two-qubit states are presented. Besides, the proposed schemes are extended to multi-sender and the partially entangled quantum resources. [ABSTRACT FROM AUTHOR]

Quantum one-way functions play a fundamental role in cryptography because of its necessity for the secure encryption schemes taking into account the quantum computer. In this paper our purpose is to establish a theoretical framework for a candidate of the quantum one-way functions and quantum trapdoor functions based on one-parameter unitary groups. The dynamics of parameterized unitary groups ensure the one-wayness and quantum undistinguishability in different levels, and the physical feasibility are derived from the simultaneous approximation of its infinitesimal generators. Moreover, these special functions are used to construct new cryptosystems-the quantum public-key cryptosystems for encrypting both the classical and quantum information. [ABSTRACT FROM AUTHOR]

Abstract: Our concern is to remotely prepare a four-particle entangled cluster-type state with high success probabilities. By constructing some useful measurement bases, two novel schemes via different entanglement resources as the quantum channel are designed: one is via an EPR pair and two three-particle GHZ states; the other is via two four-qubit GHZ states. It is shown that through four-particle projective measurements under the novel sets of mutually orthogonal basis vectors, the original state can be successfully prepared with the probabilities and 1, respectively. These schemes are extended to the non-maximally entangled quantum channel. Compared with the previous remote preparation proposal, the success probabilities of the proposed schemes are greatly improved. Furthermore, the classical communication costs of these schemes are calculated to determine the classical resources required. [Copyright &y& Elsevier]

Perfect teleportation and superdense coding are discussed via a special kind of W-state. It is shown that the state can be used for perfect teleportation of the state x|0〉⊗N + y|1〉⊗N. And the state can be utilized for superdense coding. Moreover, it is demonstrated that the sender can transmit N classical bits to the receiver by sending N − 1 qubits. [ABSTRACT FROM AUTHOR]

Utilizing W state, which is much more robust than GHZ state, we propose a protocol for three-party controlled quantum secure direct communication (QSDC). The feature of this protocol is that the sender encodes the secret message directly on a sequence of particle states and faithfully transmits them to an arbitrary one of two receivers without revealing any information to a potential eavesdropper. On the other hand, we construct the efficient quantum circuit to implement the QSDC by means of primitive operations in quantum computation. [ABSTRACT FROM AUTHOR]

Abstract: A protocol for three-party controlled quantum teleportation is discussed. It is shown that an unknown two-particle entanglement can be teleported to any one of two receivers via the only one three-particle W state. We summarize all different unitary transformations performed by the receiver with a concise formula. The quantum circuits for the generalized measurement described by positive operator-valued measure (POVM), which is utilized to probabilistically distinguish the two non-orthogonal states, are explicitly constructed by means of quantum Toffoli gates. The efficient quantum circuits for implementing the teleportation are also provided. [Copyright &y& Elsevier]

Abstract: In 2007, Wang et al. [M. Y. Wang and F. L. Yan, Chin. Phys. Lett. 24 (2007) 2486] proposed a three-party simultaneous quantum secure direct communication (3P-SQSDC) scheme with EPR pairs. Recently, Chong et al. [S. K. Chong and T. Hwang, Opt. Commun. OPTICS-15438 (2010(online))] proposed an enhancement on Wang et al.''s scheme. The communications in Chong et al.''s 3P-SQSDC can be paralleled and thus their scheme has higher efficiency. However, we find that both of the schemes have the information leakage, because the legitimate parties'' secret messages have a strong correlation. This kind of security loophole leads to the consequence that any eavesdropper (Eve) can directly conjecture some information about the secrets without any active attack. [Copyright &y& Elsevier]

Abstract: A multi-user quantum key distribution protocol [C.H. Hong et al., Opt. Commun. 283 (2010) 2644] was proposed, in which any two among n users of the system can communicate with each other, even though there is no direct quantum channel between them. Nevertheless, we show that the mediator Trent, who performs entanglement swapping in this protocol, has a way to eavesdrop on the communication between the two users without being detected. We also give an effective method to solve the security leak. [Copyright &y& Elsevier]