Quantum Bidirectional Secure Direct Communication via Entanglement Swapping

In light of a quantum secure direct communication （QSDC） scheme using entanglement swapping [Chin. Phys. Lett. 22 （2005）18], by introducing additional local operations for encoding, we propose a bidirectional QSDC （BQSDC） protocol, in which two legitimate users can simultaneously exchange their respective messages. The rule for the users to retrieve his/her partner＇s messages is derived explicitly in the most general case. Eve＇s commonly used attack method has been discussed and can be detected with the security checking process.     

Quantum Secure Direct Intercommunication with Superdense Coding and Entanglement Swapping

A quantum secure direct intercommunication scheme is proposed to exchange directly the communicators' secret messages by making use of swapping entanglement of Bell states. It has great capacity to distribute the secret messages since these messages have been imposed on high-dimensional Bell states via the local unitary operations with superdense coding. The security is ensured by the secure transmission of the travel sequences and the application of entanglement swapping.     

Quantum Secure Direct Intercommunication with Superdense Coding and Entanglement Swapping

A quantum secure direct intercommunication scheme is proposed to exchange directly the communicators＇ secret messages by making ase of swapping entanglement of Bell states. It has great capacity to distribute the secret messages since these messages have been imposed on high-dimensional Bell states via the local unitary operations with superdense coding. The security is ensured by the secure transmission of the travel sequences and the application of entanglement swapping.     

Cooperative Quantum Two-Way Communications via Quantum Teleportation Based on Brown State with the Partial Entanglement Analysis

We demonstrate two explicit cooperative two-way quantum communications based on the Brown state in a forward-and-backward fashion. One realizes the duplex exchange of an arbitrary unknown state and a certain state between Alice and Bob with the aid of the trusty Charlie via the partial entanglement analysis. The other realizes the half-duplex exchange of arbitrary unknown states. Their securities are both guaranteed due to the fact that each participant either faithfully recovers the transmitted unknown states after performing some suitable unitary operations in a deterministic way or, in a case of any irregularity, generates no results. In addition, the present half-duplex cooperative quantum communication can be similarly extended for transmitting arbitrary unknown states via the two-way quantum teleportation based on the generalized Brown-like state in a probabilistic way.     

Secure Fiberoptic Communications

At the heart of our current information explosion is the communication network. Networks are now an intrinsic part of our daily activities, whether they are for Internet business transactions or military communications in Future Combat Systems. Protection of this communication infrastructure is a must.

In this article, we discuss two approaches for securing all-optical networks. The first is an optical encryption technique that denies the information to intruders. The second is an authentication scheme capable of detecting and identifying unauthorized users.     

Quantum Version of a Generalized Monty Hall Game and Its Possible Applications to Quantum Secure Communications

In this work, the authors propose a quantum version of a generalized Monty Hall game, that is, one in which the parameters of the game are left free and not fixed on its regular values. The developed quantum scheme is then used to study the expected payoff of the player, using both a separable and an entangled initial‐state. In the two cases, the classical mixed‐strategy payoff is recovered under certain conditions. Lastly, the authors extend the quantum scheme to include multiple independent players, and use this extension to sketch two possible application of the game mechanics to quantum networks, specifically, two validated, multi‐party, key‐distribution quantum protocols.     

Quantum Entanglement Oscillations

Quantum entanglement is shown to exist as a means of lowering ground state energy for multi-component systems. Symmetric and anti-symmetric system wavefunctions are thus simply due to the inter-particle potential and not to fundamental particle types: fermions and bosons. The paper shows that additionally to the cases known, bosons— apart from the condensate minimum, can exhibit an energy minimum type allowing entanglement oscillations. This fundamentally new case could conceivably be the origin of the conflicting properties observed in super-solidity: lower (fluid-like) rotational inertia (Kim and Chan in Nature 427:225, 2004; J. Low Temp. Phys. 138:859, 2005), higher (solid-like) shear modulus (Chan in Science 319:29, 2008).     

Entanglement of Formation for Quantum States

We investigate the entanglement of formation for a class of high-dimensional quantum mixed states. We present a kind of generalized concurrence for a class of high-dimensional quantum pure states such that the entanglement of formation is a monotonically increasing convex function of the generallzed concurrence, from the monotonicity and convexity the entanglement of formafion for a class of high-dimensional mixed states has been calculated analytically,     

Role of Covariance Correlation Tensor in Establishment of Criterion of Quantum Entanglement

This article discusses the role of covariance correlation tensor in the establishment of the criterion of quantum entanglement. It gives a simple example to show the powerfulness in the treatment of quantum dense coding, and illustrates the fact that this method also provides theoretical basis for establishing corresponding knotted pictures.     

Role of Covariance Correlation Tensor in Establishment of Criterion of Quantum Entanglement

This article discusses the role of covariance correlation tensor in the establishment of the criterion of quantum entanglement. It gives a simple example to show the powerfulness in the treatment of quantum dense coding,and illustrates the fact that this method also provides theoretical basis for establishing corresponding knotted pictures.     

Criterion for Genuine Multipartite Entanglement Quantum Channels

We introduce a character matrix for the N-qubit subsystem of a 2N-qubit state and show the criterion for genuine entanglement channel existing between two N-qubit subsystems in the state. The criterion allows us to check conveniently whether genuine quantum channels exist or not in the 2N-qubit state without calculating its N-qubit reduced density matrices.     

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 Entanglement in Concept Combinations

Research in the application of quantum structures to cognitive science confirms that these structures quite systematically appear in the dynamics of concepts and their combinations and quantum-based models faithfully represent experimental data of situations where classical approaches are problematical. In this paper, we analyze the data we collected in an experiment on a specific conceptual combination, showing that Bell’s inequalities are violated in the experiment. We present a new refined entanglement scheme to model these data within standard quantum theory rules, where ‘entangled measurements and entangled evolutions’ occur, in addition to the expected ‘entangled states’, and present a full quantum representation in complex Hilbert space of the data. This stronger form of entanglement in measurements and evolutions might have relevant applications in the foundations of quantum theory, as well as in the interpretation of nonlocality tests. It could indeed explain some non-negligible ‘anomalies’ identified in EPR-Bell experiments.     

Quantum Entanglement Under Lorentz Transformation

We study the properties of quantum entanglement in moving frames, with a non-maximally entangled bipartite state: $|\phi\rangle=\sqrt{1-\varepsilon}|{\uparrow\uparrow}\rangle +\sqrt{\varepsilon}|{\downarrow\downarrow}\rangle$ , (0<ε<1). We calculate the concurrence of this state under Lorentz transformation and show that if the momenta part of the spin-1/2 pair is appropriately correlated, the concurrence is invariant ( $\mathcal {C}(\rho)=2\sqrt{\varepsilon-\varepsilon^{2}}$ ); despite the entanglement of this state is not maximal, there is no transfer of entanglement between spin and momentum.     

Quantum Watermarking Using Entanglement Swapping

Digital watermarking is the process of embedding information into a digital signal in a way that is difficult to remove. In this article a secure quantum watermarking using entanglement swapping is proposed. Here the entanglement swapping is employed to build up a hidden layer of secure message under the conventional first layer of secure information sequence. In this protocol by insuring the security of transmission of the first layer of information sequence the security of the hidden secret messages is also proved to be reliable regardless of whether the hidden channel has been detected or not.     

General Quantum Circuits for Implementing Deterministic Entanglement Conversion

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.     

Some Aspects of Quantum Entanglement for CAR Systems

We show some distinct features of quantum entanglement for bipartite CAR systems such as the failure of triangle inequality of von Neumann entropy and the possible change of our entanglement degree under local operations. Those are due to the nonindependence of CAR systems and never occur in any algebraic independent systems. We introduce a new notion half-sided entanglement.     

Secure Quantum Private Comparison Protocol Based on the Entanglement Swapping Between Three-Particle W-Class State and Bell State

We propose a new quantum private comparison protocol with the help of a semi-honest third party (TP), enabling two participants to compare the equality of their private inputs without exposing any information about their respective private inputs. Different from previous protocols, our protocol utilizes the properties of entanglement swapping between three-particle W-Class state and Bell state. The presented protocol can ensure correctness, fairness and security. Meanwhile, all the quantum particles undergo a one-way transmission, and all the participants including TP are just required having the ability to perform Bell-state measurement and exclusive-or operation which make our protocol more feasible and efficient. At last, the security of this protocol with respect to various kinds of attacks is analyzed in detail.