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In this paper, we investigate the quantum discord for a family of three-qubit extended X-states and give analytic formulas of the quantum discord for three-qubit states in several cases, including two zero quantum discord cases and the Werner-GHZ state case. Moreover, we inspect the dynamic behavior of the quantum discord for the three-qubit states under the phase damping channel. It is shown that the frozen phenomenon of quantum discord exists for some states under phase damping channel, while it does not exist for some other states. In particular, the quantum discord of the Werner-GHZ state monotonically decreases to zero under the phase damping channel. [ABSTRACT FROM AUTHOR]

Bipolar spin systems are expected to provide a reliable and scalable platform for advances in quantum computing and nanotechnology. Thus, the survey of the dynamics of the quantum properties of such systems is of paramount importance. This work explores the dynamics of bipartite entanglement and nonclassical correlations in a dipole-dipole two spin system with Dzyaloshinsky-Moriya (DM) interaction and under the influence of the intrinsic decoherence effects. We employ logarithmic negativity to quantify quantum entanglement. Local quantum uncertainty and quantum discord are employed to capture non-classical correlations beyond entanglement in the considered system. For this purpose, we consider that the system is initially prepared in a Werner state and we explore the effect of intrinsic decoherence rate, dipolar coupling parameters between the spins, strength of the Dzyaloshinsky-Moriya interaction and the intensities of the homogeneous magnetic fields on the dynamics of the three quantifiers of correlations within the considered system. The findings reveal that intrinsic decoherence deteriorates quantum correlations, while the dipolar coupling constant diminishes the oscillatory behavior observed but enhances the robustness of bipartite entanglement and nonclassical correlations. The negative effects of the intrinsic decoherence on the quantum correlations can be mitigated by adjusting the values of the system’s parameters as well as the Dzyaloshinsky-Moriya coupling parameter. We also show that the three studied measures behave quasi-similarly. Finally, we depict that the amounts of entanglement and nonclassical correlations within the system are closely tied to the system’s degree of purity. [ABSTRACT FROM AUTHOR]

We study quantum discord dynamic of two atomic qubits moving inside a leaky cavity, where the two-qubit system is driven by a classical field. We suppose that the qubits are coupled to each other through dipole-dipole interaction and interacting asymmetrically with the cavity field via a two-photon relaxation. Using the time-dependent Schrödinger equation, we obtain the quantum state of the two-qubit system and study the dynamical behavior of the corresponding quantum discord. We discuss in detail the effects of the dipole-dipole interaction, atomic motion, atom-cavity coupling strength, classical driving and detuning between the qubit and the classical field (laser detuning) on the protection of initial qubit-qubit correlation in both the Markovian and non-Markovian regimes. We show that the dipole-dipole interaction and laser detuning destroy the initial correlation between the qubits in the stationary limit, however, the classical driving can effectively eliminate their destructive effects on the maintaining the initial correlation. [ABSTRACT FROM AUTHOR]

We study the decoherence process induced by a spin chain environment on a central spin consisting of R spins and we apply it on the dynamics of quantum correlations (QCs) of three interacting qubits. To see the impact of the initially prepared state of the spin chain environment on the decoherence process, we assume the spin chain environment prepared in two main ways, namely, either the ground state or the vacuum state in the momentum space. We develop a general heuristic analysis when the spin chain environment is prepared in these states, to understand the decoherence process against the physical parameters. We show that the decoherence process is mainly determined by the choice of the initially prepared state, the number of spins of the chain, the coupling strength, the anisotropy parameter and the position from the quantum critical point. In fact, in the strong coupling regime, the decoherence process does not appear for the environment prepared in the vacuum state and it behaves oscillatory in the case of evolution from the ground state. On the other hand, in the weak coupling regime and far from the quantum critical point, decoherence induced by the ground state is weaker than that of the vacuum state. Finally, we show that QCs are completely shielded from decoherence in the case of evolution from the W state and obey the same dynamics as the decoherence factors for the GHZ state. [ABSTRACT FROM AUTHOR]

Quantum discord is a measure of quantumness of correlations in bipartite states, which characterizes the difference between quantum mutual information and classical correlations. Based on the generators of Lie algebra s u (d) , we study the quantum discord for two families of two-qudit states with maximally mixed marginals, and derive some upper bounds of quantum discord for such states by evaluating classical correlations. Furthermore, we make a comparison among total correlations, classical correlations and quantum discord for a class of special states in high-dimensional two-partite systems. [ABSTRACT FROM AUTHOR]

We explore the monogamy of multipartite quantum discord. In the article [Quantum Science and Technology 6, 4, 045028], Guo et al. show that quantum discord for multiqubit systems is monogamous provided that it does not increase under discard of subsystems. we illustrate that the above-mentioned preconditions are valid for a family of multiqubit states. Based on the analytical expressions of quantum discord and geometric discord of the family of states obtained in the articles [Phys. Rev. A 104, 012428] and [arXiv:], we investigate the dynamic behavior of these under the local decoherence channel, and show that the quantum discord of even partite systems have frozen phenomenon while the odd partite systems does not exist. For geometric discord, this family of states has the frozen phenomenon under local decoherence conditions. The results show that compound noises are not necessary for sudden changes in quantum correlation, and one qubit of the quantum noise is sufficient. The research of these non-loss conditions is of great significance for understanding the evolution of quantum systems in the environment. [ABSTRACT FROM AUTHOR]

Two-qubit X-state is a large class of quantum states which plays an important role in the quantification and dynamical study of quantum correlations. However, the corresponding quantification of quantum discord is still missing for bona fide discord measures, like original quantum discord, Bures distance of discord, and relative entropy of discord. In this paper, we consider the calculation of Bures distance of discord, which is a kind of correlations satisfying all criteria of a discord measure, for two-qubit X-states. Firstly, we derive explicit expression for Bures distance of discord for a kind of five-parameters family of states. Moreover, for general two-qubit X-states, we not only calculate the Bures distance of discord for a subset of two-qubit X-states by classifying and analyzing the optimal local measurements and the optimal projection operators, but also provide an analytic upper bound for entirety. [ABSTRACT FROM AUTHOR]

We study the effect of unentangled states with nonzero discord on Quantum Stackelberg duopoly game (QSD). We show that the initial state parameter and quantum discord will cause remarkable change in the Nash equilibrium of the QSD game and the profits of the two players. We also find that under certain conditions there is a 'specific point' of the initial state parameter and quantum discord. The two players have the same moves and payoffs at the 'specific point'. The QSD game can switch between the first-mover advantage game and the follower-mover advantage game when the initial state parameter and quantum discord varies from the left-hand-side regime of the 'specific point' to the right-hand-side regime. [ABSTRACT FROM AUTHOR]

A comparative study of quantum properties associated with coherent correlations between the modes of light generated by a nondegenerate parametric down-conversion process is presented. Particularly, the degree of nonclassicality that can be quantified by logarithmic negativity and quantum discord is compared, and a striking similar tendency is observed. In the same manner, a comparison of the quadrature variance, the smallest eigenvalue of the symplectic matrix and Einstein-Podolsky-Rosen (EPR) steering is made whereby a significant similarity is witnessed. The highest degree of quantum features of the radiation is in general manifested near threshold, whereas the quantifying measure related to the smallest eigenvalue of the symplectic matrix is found to capture a better degree of quantumness. Since each criterion renders only sufficient condition, it is hoped that witnessing consistent outcome across different criteria enhances the chance for experimental verification and practical application. [ABSTRACT FROM AUTHOR]

Quantum Discord (QD) is a measure of the total quantum non-local correlations of a quantum system. The formalism of quantum discord has been applied to various two-qubit mixed states and it has been reported that there is a non-zero quantum discord even when the states are unentangled. To this end, we have calculated the Quantum Discord for a higher than two qubit mixed state, that is, the generalized n-qubit Werner state with a bipartite split. We found that the QD saturates to a straight line with a unit slope in the thermodynamic limit. Qualitative studies of entanglement between the two subsystems using logarithmic negativity revealed that the entanglement content between them increases non-uniformly with the number of qubits leading to its saturation. We have proved the above claims both analytically and numerically. [ABSTRACT FROM AUTHOR]

In this paper, we discuss four measures for the quantum and classical correlations of two atoms in a system of two entangled atoms interacting with the Pólya field state. In five different initial states of the two atoms, we compare and analyze the influence of the atomic and optical field parameters on the time evolution of the quantum correlation and the classical correlation between two entangled atoms in the considered system. The results show that though the atomic state is initially in a separate one, the time evolution of geometrical quantum discord (GQD), concurrence (C), quantum discord (QD) can still exhibit non zero quantum correlation behavior. The results also show that the time evolution of the three measures of quantum correlation has obvious consistency but the time evolution of classical correlation (CC) is different from that of quantum correlation in the mentioned cases. In addition, the two atoms always remain in the maximum entangled state during the evolution as the two atoms are initially in a maximum entangled state Ψ 4 . [ABSTRACT FROM AUTHOR]

In this paper, a quantum correlations analytical treatment for a family of two-ququart states are presented. For this purpose, a family of two-ququart quantum states, as well as a set of von Neumann measurements are proposed. A quantum discord analytical treatment is derived for this family of two-ququart states. Finally, the classical mutual information, the entanglement of formation and quantum discord are illustrated in this family of two-ququart quantum states. [ABSTRACT FROM AUTHOR]

Quantum discord is an effective measure of quantum correlation introduced by Olliver and Zurek. We evaluate analytically the quantum discord for a large family of non-X-states. Exact solutions of the quantum discord are obtained for four parametric spaces of non-X-states. Dynamic behavior of the quantum discord is also explored under the action of the Kraus operator. [ABSTRACT FROM AUTHOR]

The geometry of the structure of entanglement and discord for Bell-diagonal states is depicted by Lang and Caves (Phys. Rev. Lett. 105, 150501, 2010). In this paper, we investigate the geometry with respect to several distance-based quantifiers of coherence for Bell-diagonal states. We find that as both l1 norm and relative entropy of coherence vary continuously from zero to one, their related geometric surfaces move from the region of separable states to the region of entangled states, a fact illustrating intuitively that quantum states with nonzero coherence can be used for entanglement creation. We find the necessary and sufficient conditions that quantum discord of Bell-diagonal states equals to its relative entropy of coherence, and depict the surfaces related to the equality. We give surfaces of relative entropy of coherence for X states. We show the surfaces of dynamics of relative entropy of coherence for Bell-diagonal states under local nondissipative channels and find that all coherences under local nondissipative channels decrease. [ABSTRACT FROM AUTHOR]

We process comparatively the time evolution of quantum discord, quantum entanglement and Wigner function for GHZ-type coherent states independently interacting with dephasing reservoirs and we address the influence of both Markovian and non-Markovian environments on their evolution. As a matter of fact, we show that in open multipartite systems negativity of Wigner function is sensitive not only to quantum entanglement but also to quantum discord. Indeed, we deem that the Wigner function can be used to capture and quantify general quantum correlations in open multipartite systems. [ABSTRACT FROM AUTHOR]

We investigate pairwise entanglement and quantum discord (QD) in the XY spin model with anisotropic three-site interaction at zero and finite temperatures. For both the nearest-neighbor spins and the next nearest-neighbor spins, special attention is paid to the dependence of entanglement and QD on the anisotropic parameter δ induced by the next nearest-neighbor spins. We show that the behavior of QD differs in many ways from entanglement under the influences of the anisotropic three-site interaction at finite temperatures. More important, comparing the effects of δ on the entanglement and QD, we find the anisotropic three-site interaction plays an important role in the quantum correlations at zero and finite temperatures. It is found that δ can strengthen the quantum correlation for both the nearest-neighbor spins and the next nearest-neighbor spins, especially for the nearest-neighbor spins at low temperature. [ABSTRACT FROM AUTHOR]

Several spin chains with 4 and 6 qubits are considered under the effect of Hamiltonian XY model and Dzyaloshinskii-Moriya (DM) interaction. In this paper, the time evolution of entanglement and quantum discord (quantum correlations) are studied. It is shown that quantum discord is more stable than entanglement. Also the effect of DM interaction depends on initial state and it may improve quantum correlations in spin chains with more than 3 qubits. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of the spin squeezing parameter γ, the external magnetic field B and the temperature T on the concurrence (C), the quantum discord (QD), and the geometric quantum discord (GQD) in the two-qubit two-axis spin squeezing model in thermal equilibrium under an external magnetic field. The results show that the spin squeezing parameter γ has a positive effect on all three correlations. When the system is in the ground state, the external magnetic field B has a weakening effect on the three types of quantum correlations. Particularly, the spin squeezing parameter can be used to alleviate the destructive effect of the magnetic field on the geometric quantum discord. At a relatively high temperature, the externally applied magnetic field B helps enhance the quantum discord (QD). Further, the quantum discord is more robust than concurrence, and thus is more suitable for use as a quantum resource in information processing. [ABSTRACT FROM AUTHOR]

We investigate the dynamics of quantum discord using an exactly solvable model where two qubits coupled to independent thermal environments. The quantum discord is employed as a non-classical correlation quantifier. By studying the quantum discord of a class of initial states, we find discord remains preserve for a finite time. The effects of the temperature, initial-state parameter, system-reservoir coupling constant and temperature difference parameter of the two independent reserviors are also investigated. We discover that the quantum nature loses faster in high temperature, however, one can extend the time of quantum nature by choosing smaller system-reservoir coupling constant, larger certain initial-state parameter and larger temperature difference parameter. [ABSTRACT FROM AUTHOR]

Recently, the effect of initial qubit-reservoir correlation for two qubits in a common reservoir on the entanglement dynamics has been studied by Yan and Xia (Acta Sinica Quantum Optica 20, 16 ). We extend their results and investigate how the initial qubit-reservoir correlation and dipole-dipole interaction between two qubits effect on dynamics of quantum discord in Markovian and non-Markovian regimes, respectively. The results show that in general, the larger initial qubit-reservoir correlation and dipole-dipole interaction can retard the decay of quantum discord. Besides, a combination of relatively strong dipole-dipole interaction and non-Markovian effect can efficiently protect quantum discord. Finally,thecomparisonbetweenevolutionsofquantumdiscordandentanglementisalsoconsidered. [ABSTRACT FROM AUTHOR]

By considering a s-wave Bardeen-Cooper-Schrieffer superconductor, as a many body system, subject to a weak constant external potential, U, using perturbed linearized Gorkov equations at zero temperature and calculating perturbed Green's functions up to the first approximation, we obtain the two-particle space-spin density matrix of the system. Then, we investigate the effect of the potential on bipartite entanglement (via concurrence) of electron spins of a Cooper pair and also quantum discord in terms of the potential and the relative distance of electrons of a Cooper pair, r. At some fixed values of r, concurrence is zero and does not change until U increases and receives to a special value. Specially, quantum entanglement length and quantum correlation length (in which quantum discord becomes zero) with respect to the potential are derived. We result that by increasing the potential, these lengths are increased. At higher values of U, quantum correlation length is not very sensitive to changes in U. Finally, the relation between these lengths is given. [ABSTRACT FROM AUTHOR]

We study the geometric measure of quantum discord of total Dirac fields in noninertial frames. As a comparison, we also calculate the corresponding geometric measure of entanglement of the same system. We discuss the properties of geometric measure of quantum discord and geometric measure of entanglement for this system with acceleration parameter and the parameter describing the entangle degree of the system in detail. Our results show that from an overall perspective, two geometric measures have similar behavior with the variation of the entangle parameter and the acceleration parameter. We find that this tripartite system is monogamous for the geometric measure of quantum discord. [ABSTRACT FROM AUTHOR]

In this study, we explore the tripartite quantum correlations by employing the quantum relative entropy as a distance measure. First, we evaluate the explicit expression for nonlinear entanglement witness (EW) of tripartite systems in the four dimensional space that lends itself to a straightforward algorithm for finding closest separable state (CSS) to the generic state. Then using nonlinear EW with specific feasible regions (FRs), quantum discord is derived analytically for the three-qubit and tripartite systems in the four dimensional space. Furthermore, we explicitly figure out the additivity relation of quantum correlations in tripartite systems. [ABSTRACT FROM AUTHOR]

We study the dynamics of quantum entanglement and quantum discord between two non-interacting qubits, which couple with two independent spin baths, obeying the XXZ Hamiltonian. After the Holstein-Primakoff transformation, one could reduce the spin bath to a single-mode bosonic bath field. Then we use this model to study the entanglement and discord dynamics of two qubits in their corresponding spin bath. For the initial Werner state, it is indicated that both entanglement and quantum discord exhibit death and revival behavior, while the quantum correlations change more smaller. [ABSTRACT FROM AUTHOR]

Quantum correlation dynamics in an anisotropic Heisenberg XYZ model under decoherence is investigated with the use of concurrence C and quantum discord (QD). With the Werner state as the initial state, we discuss the influence of mixture degree r on the dynamics. There are some difference between the time evolution behaviors of these two correlation measures with different value of r. For 0 ≤ r ≤ 1/3, there exists quantum discord but no entanglement; For 1/3< r<1, there is a 'entanglement sudden death and birth' phenomenon in the concurrence but not in the QD; For r=1, there is one interesting thing that the concurrence decays from 1 to a minimum value close to 0 but the QD vanish. In addition, we have investigated the influence of different parameters on the two correlation measures. It has been found that, the concurrence and QD both exhibit osillatory behaviors with the time evolution, which is independent on the magnetic field B and the coupling coefficient J . However, the Dzyaloshinskii-Moriya interaction (D) and coupling coefficient J have strong influence on concurrence and QD. With the increasing of the D or J, the frequency of the oscillation getting larger. When time is fixed, with the increasing of D or J, the concurrence and QD change periodically. [ABSTRACT FROM AUTHOR]

We study the dynamical evolution of quantum correlations between two central spins independently coupled to a common bath, which are represented by quantum entanglement and quantum discord. According to the results of the exact solution, we show that quantum discord is more robust and includes richer correlation than quantum entanglement due to the nonvanishing quantum correlation in the region of entanglement death, i.e., the separable states maybe contain nonclassical correlations. We discuss the effects of the intrinsic properties of the bath on quantum correlation between the two central spins in the XY and XXZ model baths. At the low temperature, the central system can keep the good quantum correlation. With the more spin number in the bath, the dynamical evolution of quantum correlation can be bounded with the small oscillation and finally approaches a stable value. In addition, we find that the interaction between the central spins and the bath in the z direction has the significant effects on quantum correlation of the central spin system. [ABSTRACT FROM AUTHOR]

Using the concurrence (C) and quantum discord (QD) criterions, the quantum correlation properties in two qubits one-axis spin squeezing model with an external magnetic field are investigated. It is found that one obvious difference in the limit case T → 0 (ground state) is the sudden disappearance phenomenon (SDP) occured in the behavior of C, while not in QD. In order to further explain the SDP, we obtain the analytic expressions of ground state C and QD which reveal that the SDP is not really 'entanglement sudden disappeared', it is decayed to zero very quickly. Proper tuning the parameters μ(the spin squeezing interaction in x direction) and Ω(the external magnetic field in z direction) not only can obviously broaden the scope of ground state C exists but also can enhance the value of ground state QD. For the finite temperature case, one evident difference is that the sudden birth phenomenon (SBP) is appeared in the evolution of C, while not in QD, and decreasing the coupling parameters μ or Ω can obviously prolong the time interval before entanglement sudden birth. The value of C and QD are both enhanced by increasing the parameters μ or Ω in finite temperature case. In addition, through investigating the effects of temperature T on the quantum correlation properties with the variation of Ω and μ, one can find that the temperature scope of C and QD exists are broadened with increasing the parameters μ or Ω, and one can obtain the quantum correlation at higher temperature through changing these parameters. [ABSTRACT FROM AUTHOR]

Present work is an attempt to compare quantum discord and quantum entanglement of quasi-Werner states formed with the four bipartite entangled coherent states (ECS) used recently for quantum teleportation of a qubit encoded in superposed coherent state. Out of these, the quasi-Werner states based on maximally ECS due to its invariant nature under local operation is independent of measurement basis and mean photon numbers, while for quasi-Werner states based on non-maximally ECS, it depends upon measurement basis as well as on mean photon number. However, for large mean photon numbers since non-maximally ECS becomes almost maximally entangled therefore dependence of quantum discord for non-maximally ECS based quasi-Werner states on the measurement basis disappears. [ABSTRACT FROM AUTHOR]

By taking into account the quantum erasing effect(QEE), the quantum discord (QD) behavior of a two-qubit system with different initial states are investigated in detail. We find that the quantum correlation can be saved under a scheme of two spatially separated atoms, each located in a leaky cavity through the quantum erasing method. It is shown that QEE can weaken the effects of decoherence, and preserve the maximum information of the coherent item. No matter whether the two atoms are in the mixted or pure state, one can robusty save their initial quantum correlation even the number of erasing events is finite. If one limit the erasing events N → ∞, the QEE can be used to protect the initial quantum correlation independently of the state in which it is stored, the values of QD is always nearly equal to the initial QD values, and it is nearly independent of the decoherence, which imply us more encourage strategy for protecting the quantum correlation properties in some quantum systems. [ABSTRACT FROM AUTHOR]

By taking into account the intrinsic decoherence and the external magnetic field, quantum discord(QD) behaviors in two-qubit spin squeezing model are investigated in detail. It is found that the magnitude of quantum discord is strongly dependent on the initial states, the squeezing interaction μ, the magnetic field Ω and the purity r of initial states. With t → ∞, one can obtain the steady quantum discord (SQD) value, the environmental decoherence cannot entirely destroy the quantum correlation. Based on the analysis of the SQD, the conditions about the existence of SQD are obtained with different initial states. Varying the parameters μ, Ω and r not only can weaken the effects of decoherence but also can improve the magnitude of QD and SQD. The effects of the parameters μ and Ω on the QD and SQD display so different and complicated features that one cannot get an uniform law about them, while the values of QD and SQD are improved with increasing r. Properly tuning the parameters μ, Ω and r, one can obtain a larger value of QD or SQD. [ABSTRACT FROM AUTHOR]

We study the dynamics of quantum correlations involving entanglement and discord of two pairs of two-level atoms in cavity QED. In the model, two atoms A and C are coupled with a single-mode cavity field via Tavis-Cumming interaction at one location, and the same for B and D at another location. The two locations are connected by the entanglement of the atoms AB and CD while there are no any direct interactions between them. Through comparing the robustness of entanglement and discord of the atoms in various initial conditions of cavities, it is shown the discord is more robust than the entanglement and would be useful in quantum information technology. [ABSTRACT FROM AUTHOR]

The goal of this work is to investigate quantum entanglement and quantum discord of a pair of two-level atoms which is driven by an external classical field and interacts with a cavity field. After extracting density matrix of the atom-atom subsystem, it is shown that we have stronger quantum discord by increasing atom-field coupling constant for the case in which there is no entanglement. Moreover, for the atom-atom subsystem it is realized that quantum entanglement and quantum discord cannot increase, they decrease after passing some times due to cavity dissipation. Also quantum entanglement and quantum discord decrease faster by increasing atom-field coupling constant. [ABSTRACT FROM AUTHOR]

In this study, using the concept of relative entropy as a distance measure of correlations we investigate the important issue of evaluating quantum correlations such as entanglement, dissonance and classical correlations for 2-dimensional Bell-diagonal states. We provide an analytical technique, which describes how we find the closest classical states(CCS) and the closest separable states(CSS) for these states. Then analytical results are obtained for quantum discord of 2-dimensional Bell-diagonal states. As illustration, some special cases are examined. Finally, we investigate the additivity relation between the different correlations for the separable generalized Bloch sphere states. [ABSTRACT FROM AUTHOR]

We revisit the quantum discord, quantum entanglement and local hidden variable models in quantum mechanics, and present a kind of understanding of quantum states from the view of correlations given by the probability distributions of local measurements outcomes. [ABSTRACT FROM AUTHOR]

We evaluate the geometric measure of entanglement for a superposition of multipartite pure GHZ coherent states. The study is done to show the entanglement behavior for different dimensions of multipartite states using continuous variables. Also, the quantum correlations change in the mixture case is studied, by proposing a model of quantum discord calculation for multipartite mixed GHZ coherent states which will be compared with the entanglement in a particular example of tripartite system. We note that our choice of isotropic mixed family states gives as a major advantage of controlling the correlations by the mixing parameter control. [ABSTRACT FROM AUTHOR]

Recent studies on quantum Fisher information (QFI) have been focused mostly on qubit systems within the context of how entanglement helps surpassing the classical limit of separable states and the limit that a given entangled system can achieve for parameter estimation. However, there are only a few works on bound entangled systems. In this work, we study the QFI of a system of the smallest dimension that bound entanglement can be observed: A bipartite quantum system of two particles of three-levels each. An interesting property of this state is that depending only on a parameter, the state can be separable, bound entangled or free entangled. We show that QFI exhibits a smooth and continues increase with respect to this parameter throughout the transition from separable to bound entangled and from bound entangled to free entangled regions. We show that in any region, this state is not useful for sub-shot noise interferometry. We also relate the QFI of this state with its geometric discord and show how these two properties exhibit a similar behavior throughout this transition. [ABSTRACT FROM AUTHOR]

In this article, we investigate the error bound of quantum discord, obtained from the analytic formula of Ali et al. (Phys. Rev. A 81, 042105, ) for the case of general X states and from the analytic formula of Fanchini et al. (Phys. Rev. A 81, 052107, ) for the case of symmetric X states. For this purpose we consider 3-element POVM. We find that the results of Ali et al. and Fanchini et al. may have the worst-case errors of 0.004565 and 0.0009, respectively. [ABSTRACT FROM AUTHOR]

Photosynthesis is one of the ancient biological processes, playing crucial role converting solar energy to cellular usable currency. Environmental factors and external perturbations has forced nature to choose systems with the highest efficiency and performance. Recent theoretical and experimental studies have proved the presence of quantum properties in biological systems. Energy transfer systems like Fenna-Matthews-Olson (FMO) complex shows quantum entanglement between sites of Bacteriophylla molecules in protein environment and presence of decoherence. Complex biological systems implement more truthful mechanisms beside chemical-quantum correlations to assure system's efficiency. In this study we investigate thermal quantum correlations in FMO protein of the photosynthetic apparatus of green sulfur bacteria by quantum discord measure. The results confirmed existence of remarkable quantum correlations of of BChla pigments in room temperature. This results approve involvement of quantum correlation mechanisms for information storage and retention in living organisms that could be useful for further evolutionary studies. Inspired idea of this study is potentially interesting to practice by the same procedure in genetic data transfer mechanisms. [ABSTRACT FROM AUTHOR]

We investigate the thermal quantum correlations in the Heisenberg XX spin chain, and the teleportation of a two-qubit entangled state via the spin chain is analyzed. It is found that the effects of external magnetic field and three-site interaction on the thermal entanglement and quantum discord between the nearest or the next nearest neighbor qubits behave differently in various aspects. Special attention is paid to how to enhance the quantum correlations of the output state and the average fidelity of the teleportation. We find that quantum discord gives a better performance in the quantum correlations transmission, and the three-site interaction is necessary for a successful teleportation. [ABSTRACT FROM AUTHOR]

This paper examines the quantum correlations of the Werner state and demonstrates the relationship between the quantum discord and entanglement under decoherence. We also identify that when the discord takes the maximal value for a given state, and discuss the boundary value for entanglement and discord. As we all know that, in an ideal environment, the quantum discord is always larger than the entanglement of formation for almost all entangled states. But, the analysis in the article exposes that the entanglement may show stronger anti-interference than quantum discord in the noisy channel. In addition, the emphasis is also placed on the problem of the relation between the geometric discord ( D) and the entanglement of formation (EOF) which is customarily used as a measure of entanglement. At the same time, we also investigate the inequality 2 D ≥ N and find that it is still be satisfied under the phase flip channel. [ABSTRACT FROM AUTHOR]

For carrying out many quantum information protocols entanglement must be established in advance between two distant parties. Practically, inevitable interaction of entangled subsystems with their environments during distribution and storage will result in degradation of entanglement. Here we show that some partially entangled states are more robust than maximally entangled states in terms of the residual quantum correlation measured by concurrence, fully entangled fraction, and quantum discord, respectively. This phenomenon leads to the fact that nonmaximally entangled states can outperform maximally entangled states for quantum correlation distribution and storage under the amplitude damping. These results can also educe a noticeable consequence that the ordering of states under quantum correlation monotones can be reversed even by local trace-preserving and completely positive maps. [ABSTRACT FROM AUTHOR]

Assuming a two-qubit system in Werner state which evolves in Heisenberg XY model with Dzyaloshinskii-Moriya (DM) interaction under the effect of different environments. We evaluate and compare quantum entanglement, quantum and classical correlation measures. It is shown that in the absence of decoherence effects, there is a critical value of DM interaction for which entanglement may vanish while quantum and classical correlations do not. In the presence of environment the behavior of correlations depends on the kind of system-environment interaction. Correlations can be sustained by manipulating Hamiltonian anisotropic-parameter in a dissipative environment. Quantum and classical correlations are more stable than entanglement generally. [ABSTRACT FROM AUTHOR]

The quantum correlations (QC) of two two-level atoms interacting with a single mode vacuum field are investigated. The relationship between the quantum discord (QD) and the entanglement of formation (EOF), the influence of the atomic dipole-dipole interaction along with two-atom initial states on QC of two atoms are discussed. The results indicate that when two-atom is initially in an entangled state, QD is consistent with EOF. Compared with the quantumness of correlations, the latter is always larger than the former, and the larger the initial QE, the larger the QD. Meanwhile, there is no occurrence of sudden death phenomenon of QC throughout the temporal evolution. Moreover, QD is more robust than QE under strong dipole-dipole interaction, and then the relative stable QC resources can be achieved. [ABSTRACT FROM AUTHOR]

In this paper, performance of the important quantum correlation measures shared by the next-to-neighbor qubits of the XY model with Dzyaloshinskii-Moriya (DM) interaction has been investigated, employing quantum renormalization group method. Through analyzing the effect of DM interaction and anisotropy parameters on the quantum discord (QD) and measurement-induced disturbance (MID), we find that MID fails to symbolize the characteristics of quantum correlation for the system. While performance of the improved version of MID, i.e. ameliorated MID (AMID), delivers more dependable consequences. On the other hand, take QD as an example we have illustrated that it can efficiently observe the quantum critical points associated with quantum phase transitions after several iterations of the renormalization. To serve as the further insight, the nonanalytic and scaling behaviors of the QD are also taken into consideration. [ABSTRACT FROM AUTHOR]

We study two coupled cavities system, each of cavity containing a single two-level atom. Quantum entanglemt, quantum discord and quantum phase transition under ground state have been investigated. Atomic excitation number variance has used to characterize the quantum phase transition. We conclude that, in our model, quantum discord have nonzero values while quantum entanglement vanish and quantum discord is a more proper measure to characterize quantum transition. [ABSTRACT FROM AUTHOR]

In this paper, the dynamics and protection of quantum discord for two uncoupled qubits driven by classical phase noisy laser(CPNL) is investigated. The results show that, the dynamics of quantum discord depends on the ratio of CPNL rate and the system-environment coupling strength. The quantum discord can be well protected by increasing the ratio in the Markovian classical noise region or by decreasing the ratio in the non-Markovian classical noise region. Besides, we explain the revivals of the quantum discord by means of the increase of parameter used to quantify non-Markovianty of the single qubit dynamics in the non-Markovian classical noise region. [ABSTRACT FROM AUTHOR]