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The uncertainty principle imposes a limitation on the measurement accuracy of two incompatible observables and has potential applications in quantum information science. We explore the bipartite entropic uncertainty relation and dense coding for two qubits coupled via dipole–dipole interaction and subject to a bosonic reservoir. It is shown that there exists a trade-off between the uncertainty bound and the dense coding capacity which results in their opposite dynamical behaviors. Moreover, the behaviors of the measurement uncertainty and the dense coding capacity rely crucially on the initial system–reservoir correlation, the strength of the dipole–dipole interaction, and the degree of non-Markovianity, and one can reduce the measurement uncertainty and enhance the dense coding capacity by tuning these parameters to appropriate values.

Quantum coherence and quantum correlations are of fundamental and practical significance for the development of quantum mechanics.They are also cornerstones of quantum computation and quantum communication theory. Searching physically meaningful and mathematically rigorous quantifiers of them are long-standing concerns of the community of quantum information science, and various faithful measures have been introduced so far. We review in this paper the measures of discordlike quantum correlations for bipartite and multipartite systems, the measures of quantum coherence for any single quantum system, and their relationship in different settings. Our aim is to provide a full review about the resource theory of quantum coherence, including its application in many-body systems, and the discordlike quantum correlations which were defined based on the various distance measures of states. We discuss the interrelations between quantum coherence and quantum correlations established in an operational way, and the fundamental characteristics of quantum coherence such as their complementarity under different basis sets, their duality with path information of an interference experiment, their distillation and dilution under different operations, and some new viewpoints of the superiority of the quantum algorithms from the perspective of quantum coherence. Additionally, we review properties of geometric quantum correlations and quantum coherence under noisy quantum channels. Finally, the main progresses for the study of quantum correlations and quantum coherence in the relativistic settings are reviewed. All these results provide an overview for the conceptual implications and basic connections of quantum coherence, quantum correlations, and their potential applications in various related subjects of physics., 82 pages, 8 figures; Final version to be published in Physics Reports

The reservoir memory effects can lead to information backflow and recurrence of the previously lost quantum correlations. We establish connections between the direction of information flow and variation of the geometric quantum discords (GQDs) measured respectively by the trace distance, the Hellinger distance, and the Bures distance for two qubits subjecting to the bosonic structured reservoirs, and unveil their dependence on a factor whose derivative signifies the (non-)Markovianity of the dynamics. By considering the reservoirs with Lorentzian and Ohmic-like spectra, we further demonstrated that the non-Markovianity induced by the backflow of information from the reservoirs to the system enhances the GQDs in most of the parameter regions. This highlights the potential of non-Markovianity as a resource for protecting the GQDs., Comment: 6 pages, 3 figures

The one-qubit teleportation protocol is reexamined when it is executed in the presence of various decohering environments. The results revealed that this quantum protocol is more robust under the influence of dephaisng environment than those under the influence of dissipative or noisy environment. The environment may deprive the quantum advantage of teleportation over purely classical communication in a finite or infinite lifetime, which is dependent on the type of environment. Also we found that except entanglement, the purity of the entangled state resource is also crucial in determine the quality of the teleported state., Comment: 10 pages, 2 figures

By adopting the concept of fidelity, we investigated efficiency of quantum state transfer with the XX chain as the quantum channel. Different from the previous works, we concentrated on effects of spin and magnetic impurity on fidelity of quantum state transfer. Our results revealed that the spin impurity cannot prevent one from implementing perfect transfer of an arbitrary one-qubit pure state across the spin channel, however, the presence of magnetic impurity or both spin and magnetic impurities may destroy the otherwise perfect spin channels., Comment: 5 pags

We investigate disentanglement dynamics of two coupled qubits and qutrits which interact uniformly to a general XY spin-chain environment with the Dzyaloshinsky-Moriya (DM) interaction. We obtained exact expression of the time evolution operator and analyzed the dynamical process of the decoherence factors. Through explicitly calculating the concurrence and the negativity, we examined disentanglement behaviors of two coupled central spins evolve from different initial pure states, which are found to be nontrivially different from those of the uncorrelated ones, in particular, the enhanced decay of the entanglement induced by quantum criticality of the surrounding environment may be broken by introducing self-Hamiltonian of the central spin system. Moreover, the DM interaction may have different influences on decay of the entanglement depending on the strength of the system-environment coupling, the anisotropy of the environmental spin chain and the intensity of the transverse magnetic field, as well as the explicit form of the initial states of the central spin system., Comment: 16 pages, 10 figures

We propose the tensor representation of teleportation and controlled teleportation. By using this representation, it is easy to describe the process of teleporting an unknown N-qubit state via a genuine 2Nqubit channel, and to find the necessary and sufficient condition of realizing a successful teleportation (which is determined by the measurement matrix T

We propose a scheme to enhance the entanglement of a dissipative system, and the enhancement is happened during certain intervals of the evolution time. Our method is obtained by introducing one impurity into a Heisenberg XY chain and then solving the Lindblad form of the master equation with different initial states. The dynamics of entanglement reveal that one can significantly enhance the entanglement. This result will be helpful for the generation and transportation of entanglement in real solid-state systems.

Entanglement dynamics of the N-qubit XY model in thermal and dephasing environments are investigated by solving the Lindblad form of the master equation. Analytical solutions for the two-qubit case and numerical solutions for the multi-qubit case are obtained. For the two-qubit case, our results revealed two main features for entanglement evolution from different initial states. First, the thermal reservoir always induces degradation of the entanglement, and the entanglement may undergo sudden death during certain intervals of the evolution time. Second, the dephasing environment induces damped oscillation of the entanglement for initially separable states and mixed states with relative large values of Δ or J; however, it always induces exponentially decay of the entanglement for the initial Bell states. For the multi-qubit case, our results show that the entanglement decreases monotonically as the time evolves for the initial W state, and behaves as damped oscillation for the initial “one-particle” state. Particularly, for system with large number of qubits, the curves of the concurrence C12 with different N are almost overlapped in dephasing environment.

By analyzing parameter-dependence of the linear entropy and the negativity of a block of L/2 odd-number spins, we study quantum phase transitions (QPTs) in the spin-1/2 Heisenberg XXZ model, the dimerized Heisenberg model, the dimerized-frustrated Heisenberg model and the spin-1 quadratic–biquadratic Heisenberg model. The numerical results reveal that most of the QPTs can be detected exactly by discontinuities, singularities or extreme points of these two quantities with finite-size samples. This fact implies that the linear entropy and the negativity can serve as efficient indicators of QPTs occurring in a variety of condensed-matter systems.

By analytically solving the master equation, we examine entanglement dynamics of the two-qubit spin system coupled via the XY interaction and in the presence of population relaxation. We found that the entanglement dynamical behaviors are very sensitive to different initialized states. Particularly, for initial states ϱ=(|01〉〈01|+|10〉〈10|)/2 and ϱ=(|00〉〈00|+|11〉〈11|)/2, a combination of the XY coupling with the population relaxation can even be used to enhance the entanglement. Moreover, we show that among different initially separable states, ϱ=|01〉〈01| and ϱ=|10〉〈10| are more robust in generating pairwise entanglement.

By combining the idea of quantum secure direct communication (QSDC) and BB84 quantum key distribution (QKD), we propose a secure quantum dialogue protocol via single photons. Comparing with the previous bidirectional quantum secure communication scheme [24] in which the EPR pairs are used, our protocol is not only feasible in practice but also can overcome the drawback “information leakage” or “classical correlation”. Our scheme possesses the characters of security and high efficiency.