Quantum Remote State Preparation Based on Quantum Network Coding

As an innovative theory and technology, quantum network coding has become the research hotspot in quantum network communications. In this paper, a quantum remote state preparation scheme based on quantum network coding is proposed. Comparing with the general quantum remote state preparation schemes, our proposed scheme brings an arbitrary unknown quantum state finally prepared remotely through the quantum network, by designing the appropriate encoding and decoding steps for quantum network coding. What is worth mentioning, from the network model, this scheme is built on the quantum k-pair network which is the expansion of the typical bottleneck network—butterfly network. Accordingly, it can be treated as an efficient quantum network preparation scheme due to the characteristics of network coding, and it also makes the proposed scheme more applicable to the large-scale quantum networks. In addition, the fact of an arbitrary unknown quantum state remotely prepared means that the senders do not need to know the desired quantum state. Thus, the security of the proposed scheme is higher. Moreover, this scheme can always achieve the success probability of 1 and 1-max flow of value k. Thus, the communication efficiency of the proposed scheme is higher. Therefore, the proposed scheme turns out to be practicable, secure and efficient, which helps to effectively enrich the theory of quantum remote state preparation.     

Quantum properties and dynamics of X states

X states are a broad class of two-qubit density matrices that generalize many states of interest in the literature. In this work, we give a comprehensive account of various quantum properties of these states, such as entanglement, negativity, quantum discord and other related quantities. Moreover, we discuss the transformations that preserve their structure both in terms of continuous time evolution and discrete quantum processes.     

The evolution and stability of quantum correlations in dissipative cavity

We investigate the dynamics of quantum correlations such as entanglement and quantum discord between two atoms in a lossy cavity. It is found that a stable quantum discord could be induced even when the atoms remain separable at all times. Also, we show that it is possible to amplify and protect the quantum discord under cavity decay for certain types of initial states. Moreover, entanglement decoherence-free subspaces are obtained which may be useful in quantum information and quantum computation.     

The dynamics of entanglement and quantum discord of two atoms in coupled cavities

We investigate the dynamics of quantum correlations such as entanglement and quantum discord between two noninteracting atoms, each of which is trapped inside one of two coupled cavities. We find that the cavity decay can induce both entanglement and quantum discord between the two atoms when they are initially prepared in doubly excited state. The result shows the sudden death and sudden birth of entanglement and robustness of the quantum discord to sudden death. It is also found that the doubly excited state is responsible for the sudden death of entanglement. Moreover, the sudden death of entanglement can be controlled by the intercavity hopping rate.     

Enhancement of discord and entanglement with detuning for two coupled quantum dots in a driven cavity

We study the quantum discord for a system of two identical coupled quantum dots interacting with quantized cavity field in the presence of cavity as well as dot decay and detuning. The cavity is externally driven by a coherent light. These results are compared with the entanglement of the quantum dots in various parameter regimes in which system may or may not show bistability. We show that the discord in the steady state is nonzero for any nonzero cavity field amplitude. The system has higher discord in the upper branch of the bistability curve where the entanglement is zero. We also find many other interesting results including high discord and entanglement in the presence of detuning, a phenomenon which we further examine by approximating the density matrix in the appropriate limit.     

Quantum communications with compressed decoherence using bright squeezed light

We propose a scheme for long-distance distribution of quantum entanglement in which the entanglement between qubits at intermediate stations of the channel is established by using bright light pulses in squeezed states coupled to the qubits in cavities with a weak dispersive interaction. The fidelity of the entanglement between qubits at the neighbor stations (10 km apart from each other) obtained by postselection through the balanced homodyne detection of 7 dB squeezed pulses can reach F = 0.99 without using entanglement purification, at the same time, the probability of successful generation of entanglement is 0.34.     

Researching the Link Between the Geometric and Rènyi Discord for Special Canonical Initial States Based on Neural Network Method

Quantum correlation which is different to the entanglement and classical correlation plays important role in quantum information field. In our setup, neural network method is adopted to simulate the link between the Rènyi discord (α = 2) and the geometric discord (Bures distance) for special canonical initial states in order to show the consistency of physical results for different quantification methods. Our results are useful for studying the differences and commonalities of different quantizing methods of quantum correlation.     

Quantum Entanglement and Correlations in Superconducting Flux Qubits

We report on the quantum correlations dissipative dynamics followed by coupled superconducting flux qubits. The coupling between the superconducting quantum register and the reservoir is described by two different mechanisms: collective and independent decoherence. By means of the Bloch?CRedfield formalism, we solve the quantum master equation and show that coupling under collective quantum noise is more robust to decoherence. This result is demonstrated for different flux qubit initial preparations, taking into account the influence due to external fields and temperature. Furthermore, we compute the entanglement and the quantum discord dissipative dynamics as controlled by external parameters. We show that the discord is more robust against decoherence effects. This fact could be harnessed in the realization of quantum computing tasks that do not need to invoke entanglement in their implementation.     

Quantifying quantumness of correlations using Gaussian Rényi-2 entropy in optomechanical interfaces

Using the Gaussian Rényi-2 entropy, we analyse the behaviour of two different aspects of quantum correlations (entanglement and quantum discord) in two optomechanical subsystems (optical and mechanical). We work in the resolved sideband and weak coupling regimes. In experimentally accessible parameters, we show that it is possible to create entanglement and quantum discord in the considered subsystems by quantum fluctuations transfer from either light to light or light to matter. We find that both mechanical and optical entanglement are strongly sensitive to thermal noises. In particular, we find that the mechanical one is more affected by thermal effects than that optical. Finally, we reveal that under thermal noises, the discord associated with the entangled state decays aggressively, whereas the discord of the separable state (quantumness of correlations) exhibits a freezing behaviour, seeming to be captured over a wide range of temperature.     

Quantum entanglement criteria

Abstract

We review the main criteria used to detect entanglement in quantum systems. The main properties of each criteria are summarized depending on whether the criteria provides a sufficient or necessary condition, whether it involves density matrix or operators, or if the criteria is phase sensitive. We show that several criteria have much in common and they could be related mathematically. We also discuss the features of entanglement which are useful in quantum information technology.     

A Controlled Quantum Dialogue Protocol Based on Quantum Walks

In order to enable two parties to exchange their secret information equally, we propose a controlled quantum dialogue protocol based on quantum walks, which implements the equal exchange of secret information between the two parties with the help of the controller TP. The secret information is transmitted via quantum walks, by using this method, the previously required entangled particles do not need to be prepared in the initial phase, and the entangled particles can be produced spontaneously via quantum walks. Furthermore, to resist TP’s dishonest behavior, we use a hash function to verify the correctness of the secret information. The protocol analysis shows that it is safe and reliable facing some attacks, including intercept-measure-resend attack, entanglement attack, dishonest controller’s attack and participant attack. And has a slightly increasing efficiency comparing with the previous protocols. Note that the proposed protocol may be feasible because quantum walks prove to be implemented in different physical systems and experiments.     

Quantum information processing for ions via linear optics

We propose a linear optical scheme for the transfer of unknown ionic states, the entanglement concentration for nonmaximally entangled states for ions via entanglement swapping and the remote preparation for ionic entangled states. The joint Bell state measurement needed in the previous schemes is not needed in the current scheme, i.e. the joint Bell state measurement has been converted into the product of separate measurements on single ions and photons. In addition, the current scheme can realize the quantum information processes for ions by using linear optical elements, which simplify the implementation of quantum information processing for ions.     

Quantum Electronic Contract Scheme Based on Single Photon

An electronic contract is a contract signed by electronic means, which is widely used in electronic commerce activities. In recent years, with the rapid development of quantum cryptography technology, the quantum electronic contract has been widely studied by researchers. Supported by the basic principles of quantum mechanics, a quantum electronic contract scheme based on the single photon is proposed in this paper. In this scheme, two copies of the same contract are signed by both parties involved, and then a copy of each contract is sent to a trusted third party. The trusted third party verifies the signatures of both parties and compares the signed copies to determine whether the contract is valid. Compared with the previous scheme, this scheme is based on the quantum electronic contract signed by the single photon. Because the single photon is easy to prepare and operate, this scheme is simple and easy to implement. At the same time, the scheme does not need to exchange signatures between the two parties, which reduces the complexity of communication. Nevertheless, it requires both parties and the third party to be honest and trustworthy.     

Quantum Error Correction and Reversible Operations

This article gives a pedagogical account of Shor's nine-bit code for correcting arbitrary errors on single qubits and reviews work that determines when it is possible to maintain quantum coherence by reversing the deleterious effects of open-system quantum dynamics. The review provides an opportunity to introduce an efficient formalism for handling superoperators. Some bounds on entanglement fidelity, which might prove useful in analyses of approximate error correction, are presented and proved.     

An Efficient Quantum Key Distribution Protocol with Dense Coding on Single Photons

Combined with the dense coding mechanism and the bias-BB84 protocol, an efficient quantum key distribution protocol with dense coding on single photons (QDKD-SP) is proposed. Compared with the BB84 or bias-BB84 protocols based on single photons, our QDKD-SP protocol has a higher capacity without increasing the difficulty of its experiment implementation as each correlated photon can carry two bits of useful information. Compared with the quantum dense key distribution (QDKD) protocol based on entangled states, our protocol is more feasible as the preparation and the measurement of a single-photon quantum state is not difficult with current technology. In addition, our QDKD-SP protocol is theoretically proved to be secure against the intercept-resend attack.     

Quantum dense coding via cavity decay

We investigate a scheme for implementing quantum dense coding via cavity decay and linear optics devices. Our scheme combines two distinct advantages: the atomic qubit serves as a stationary bit and the photonic qubit as a flying bit, thus it is suitable for long distant quantum communication.     

d-Dimensional quantum secret sharing without entanglement

A d-dimensional quantum state secret sharing scheme without entanglement is proposed. In the proposed scheme, the dealer generates a single quantum state in d-dimensional Hilbert space, and performs the Pauli unitary operation on the quantum state according to the private keys of the participants. In the recovery phase, each participant performs the Pauli operation on the quantum state according to his private key, and the last participant will recover the original quantum state. Compared to the existing quantum secret sharing schemes, the main contribution of the proposed scheme is that the quantum state can be shared without the entanglement, so the sharing of the quantum state is more practical.     

Quantum Communication Networks and Trust Management: A Survey

This paper summarizes the state of art in quantum communication networks and trust management in recent years. As in the classical networks, trust management is the premise and foundation of quantum secure communication and cannot simply be attributed to security issues, therefore the basic and importance of trust management in quantum communication networks should be taken more seriously. Compared with other theories and techniques in quantum communication, the trust of quantum communication and trust management model in quantum communication network environment is still in its initial stage. In this paper, the core technologies of establishing secure and reliable quantum communication networks are categorized and summarized, and the trends of each direction in trust management of quantum communication network are discussed in depth.     

Message Authentication with a New Quantum Hash Function

To ensure the security during the communication, we often adopt different ways to encrypt the messages to resist various attacks. However, with the computing power improving, the existing encryption and authentication schemes are being faced with big challenges. We take the message authentication as an example into a careful consideration. Then, we proposed a new message authentication scheme with the Advanced Encryption Standard as the encryption function and the new quantum Hash function as the authentication function. Firstly, the Advanced Encryption Standard algorithm is used to encrypt the result of the initial message cascading the corresponding Hash values, which ensures that the initial message can resist eavesdropping attack. Secondly, utilizing the new quantum Hash function with quantum walks can be much more secure than traditional classical Hash functions with keeping the common properties, such as one-wayness, resisting different collisions and easy implementation. Based on these two points, the message authentication scheme can be much more secure than previous ones. Finally, it is a new way to design the message authentication scheme, which provides a new thought for other researchers in the future. Our works will contribute to the study on the new encryption and authentication functions and the combination of quantum computing with traditional cryptology in the future.     

Quantum correlations in cavity QED networks

We present a review of the dynamical features such as generation, propagation, distribution, sudden transition and freezing of the various quantum correlation measures, as Concurrence, Entanglement of Formation, Quantum Discord, as well their geometrical measure counterparts within the models of Cavity Quantum Electrodynamics Networks. Dissipation and thermal effects are discussed both in the generation of quantum correlations as well as their effect on the sudden changes and freezing of the classical and quantum correlations in a cavity quantum electrodynamical network. For certain initial conditions, double transitions in the Bures geometrical discord are found. One of these transitions tends to disappear at a critical temperature.