Dynamics Of Quantum Correlations Research Articles

Quantum Discord for Information Transmission Using Coherent States

We suggest theoretically the possibility to transmit information through a decohering quantum channel employing Glauber’s coherent states. In fact, we study the dynamics of quantum correlations of two-mode entangled bipartite coherent states in the presence of the amplitude damping effect. In addition, we examine the quantum correlations based on quantum discord, which is a powerful key source in quantum information processing.

Effectiveness of Non-Markovian Methods for Quantum Discord Dynamics of Non-coupled Two-Qubit System**Supported by the National Natural Science Foundation of China under Grant Nos. 11564013, 11464014, 11564012, 11602094 and the Natural Science Foundation of Hunan Province, China under Grant No. 2016JJ4073

The dissipative dynamics of non-coupled two qubits interacting with independent reservoir is studied by solving the non-Markovian master equation. In order to examine the effectiveness of the Nakajima-Zwanzig and time-convolutionless master equations in the description of quantum correlation dynamics, different coupled regimes are investigated. The comparison between the above two master equation methods for investigating the dynamics of quantum discord is also made. Finally, we further confirm that the two master equations should be applied in different regimes of qubits coupled to their reservoirs, respectively.

Decoherence for a two-qubit system in a spin-chain environment**Project supported by the National Natural Science Foundation of China (Grant No. 11404246) and the Shandong Provincial Natural Science Foundation, China (Grant No. ZR2017MF040).

The quantum coherence and correlation dynamics for a two-qubit system in the Ising spin-chain environment are studied. A sudden change of coherence is found near the critical point, which provides us with an effective way to detect the quantum phase transition. By studying the relationship between quantum discord and coherence, we find that coherence displays the behavior of classical correlation for t < t0, and of quantum discord for t > t0, where t0 is the time-point of a sudden transition between classical and quantum decoherence.

Local quantum uncertainty and trace distance discord dynamics for two-qubit X states embedded in non-Markovian environment

We investigate the behavior of quantum correlations in some specific Werner-like two-qubit states, where the qubit interacts individually with non-Markovian environment. We employ the local quantum uncertainty and trace distance discord to quantify the amount of quantum correlations between the evolved qubits and the corresponding analytical expressions are derived. For specific values of the parameters characterizing the whole system, the dynamics of quantum correlations exhibits collapse and revival phenomena. The influence of the non-Markovianity is also investigated to analyze the monotonic decay of quantum correlations in the limiting case of Markovian regime. Furthermore, we show that trace distance discord captures quantum correlations that cannot be revealed by local quantum uncertainty in some particular situations.

Dynamics of quantum correlation of atoms immersed in a thermal quantum scalar fields with a boundary

In this paper, we study the behaviors of quantum correlation for two atoms immersed in a thermal bath of quantum scalar fields in the presence of a perfectly reflecting plane boundary. We firstly discuss the solving process of master equation that governs the system evolution. Then, we analyze the creation, revival and degradation of quantum correlation for initial zero-correlation state and initial entangled state. Specially, we discuss in detail the evolution of quantum correlation in certain special conditions and models. The distance from the boundary, besides the bath temperature and the interatomic separation, gives us more freedom in controlling the behaviors of quantum correlation. Compared with the sudden death and birth of entanglement, quantum correlation changes more smoothly and thus is more robust than entanglement.

Quantum distinguishability and geometric discord in the background of Schwarzschild space–time

In this paper, the dynamics of quantum correlations is investigated in the background of Schwarzschild space–time. Utilizing geometrical trace distance, quantum correlations of interest are witnessed by distinguishability and geometric discord. The results show that in the physical accessible region the quantum correlations are dampened by the Hawking radiation, and their magnitudes are determined by the values of state parameter. Moreover, the decreasing distinguishability leads to the damping of geometric discord, and vice versa. In the physical inaccessible regions, the quantum correlations revive as the Hawking radiation enhancing, and then approach to certain constants in the infinite Hawking temperature limit. To understand the correlation dynamics systematically, we finally explore their distributions among all the bipartite divisions.

Dynamics of tripartite quantum correlations and decoherence in flux qubit systems under local and non-local static noise

We investigate the dynamics of entanglement, decoherence and quantum discord in a system of three non-interacting superconducting flux qubits (fqubits) initially prepared in a Greenberger–Horne–Zeilinger (GHZ) state and subject to static noise in different, bipartite and common environments, since it is recognized that different noise configurations generally lead to completely different dynamical behavior of physical systems. The noise is modeled by randomizing the single fqubit transition amplitude. Decoherence and quantum correlations dynamics are strongly affected by the purity of the initial state, type of system–environment interaction and the system–environment coupling strength. Specifically, quantum correlations can persist when the fqubits are commonly coupled to a noise source, and reaches a saturation value respective to the purity of the initial state. As the number of decoherence channels increases (bipartite and different environments), decoherence becomes stronger against quantum correlations that decay faster, exhibiting sudden death and revival phenomena. The residual entanglement can be successfully detected by means of suitable entanglement witness, and we derive a necessary condition for entanglement detection related to the tunable and non-degenerated energy levels of fqubits. In accordance with the current literature, our results further suggest the efficiency of fqubits over ordinary ones, as far as the preservation of quantum correlations needed for quantum processing purposes is concerned.

Quantum correlation of high dimensional system in a dephasing environment

For a high dimensional spin-S system embedded in a dephasing environment, we theoretically analyze the time evolutions of quantum correlation and entanglement via Frobenius norm and negativity. The quantum correlation dynamics can be considered as a function of the decoherence parameters, including the ratio between the system oscillator frequency ω0 and the reservoir cutoff frequency ωc, and the different environment temperature. It is shown that the quantum correlation can not only measure nonclassical correlation of the considered system, but also perform a better robustness against the dissipation. In addition, the decoherence presents the non-Markovian features and the quantum correlation freeze phenomenon. The former is much weaker than that in the sub-Ohmic or Ohmic thermal reservoir environment.

Probing the sign of the Hubbard interaction by two-particle quantum walks

We consider two identical bosons propagating on a one-dimensional lattice and address the prob- lem of discriminating whether their mutual on-site interaction is attractive or repulsive. We suggest a probing scheme based on the properties of the corresponding two-particle quantum walks, and show that the sign of the interaction introduces specific and detectable features in the dynamics of quantum correlations, thus permitting to discriminate between the two cases. We also discuss how these features are connected to the band-structure of the Hubbard Hamiltonian, and prove that discrimination may be obtained only when the two walkers are initially prepared in a superposition of localized states.

Correlation and coherence for two-qubit system coupled to XY spin chains

Quantum coherence has played a decisive role in quantum information processing. On the other hand, quantum correlation can be considered as a powerful resource for delivering quantum information. Both quantum coherence and quantum correlation may occur in an information propagating process, which challenges us to understand the relationship between coherence and correlation. This is also an important procedure for physicists to know the features of quantum resources. Any quantum system interacting with its surrounding environment will destroy the quantum coherence and fail to fulfil any task of delivering quantum information. In this sense, studying the dynamics of quantum correlation and quantum coherence is very fascinating. In this paper, we investigate the dynamics of the quantum correlation and quantum coherence for two central qubits coupled to their own spin baths modeled by the XY spin chain with Dzyaloshinsky-Moriya interaction. We employ the quantum discord to characterize the quantum correlation, and use the relative entropy to measure quantum coherence. In this way the evolution law of the quantum discord and the relative entropy of quantum coherence of two-qubit system are derived, and the evolution law depends not only on the Dzyaloshinsky-Moriya interaction, the anisotropy parameter and the total number of spin chain sites, but also on the coupling strength between the central spin and its spin chain. Our findings are as follows. Firstly, we find that near the critical point of spin chain the quantum coherence abruptly changes, which can be used to detect the existence of quantum phase transition. Secondly, at the critical point, the relative entropy of quantum coherence is the same as that of classical correlation when time tt0, and it is the same as that of quantum discord when time tt0. At time t0, the sudden transition from quantum discord to classical correlation occurs. All in all, the relative entropy of quantum coherence reflects the behaviors of classical correlation and quantum discord for times tt0 and tt0, respectively, which is caused by the change of the optimal basis for quantum discord. Thirdly, the dynamics of quantum correlation and quantum coherence keep invariant under the scaling variation of the total number of spin chain sites and the coupling strength. Moreover, we find that all the Dzyaloshinsky-Moriya interactions and the anisotropy parameters, as well as the coupling strengths will enhance the decay of quantum coherence and quantum correlation, while they have no obvious effect on the relationship between dynamics of coherence and correlation. The above discussion reveals some new features of quantum coherence and quantum correlation, which may be useful in further developing quantum information theory.

单Tavis-Cummings模型中量子关联动力学演化特性及其在量子通信中的应用

单Tavis-Cummings模型中量子关联动力学演化特性及其在量子通信中的应用

The Dynamics of Quantum Correlations in Multi-qubit Spin Chains Under the Effect of Dzyaloshinskii-Moriya Interaction

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.

Stable and metastable freezing of classical correlations in qutrits

We study the dynamics of quantum and classical correlations in a two-qutrit system coupled to independent reservoirs. In particular, we addressed the differences in the dynamics of Markovian and non-Markovian regimes and show that for specific initial states, classical correlations exhibit abrupt changes along the dynamics. A particular sudden change occurs when the classical correlations freezes to a certain value at a given time, revealing the apparition of a pointer-state basis. After this given time, the decoherence only affects quantum correlations. Here we identify two regimes in the decoherence dynamics: a mixed regime when both classical and quantum correlations decay and a quantum regime when only quantum correlations decay. We show that the freezing of classical correlations can be stable or metastable depending on the system-reservoirs parameters. In the long-time limit, we find analytical expressions for the pointer-state basis the system settles in, and consequently for classical and quantum correlations.

Dynamics super quantum discord and quantum discord teleportation in the Jaynes–Cummings model

The aim of this paper is investigation on dynamics of super quantum discord (SQD) and quantum discord (QD) teleportation in the Jaynes–Cummings model. In order to teleport one and two qubit states, a scheme is proposed for quantum channel where is induced from an atom-field interaction. The initial state of the atom is its excited state while the state of field starts in a coherent one. The model reveals that the dynamics of quantum correlations depends crucially on atom-field initial conditions and the field parameters can be utilized as control parameters for optimal teleportation. Interestingly, we find that QD teleportation and SQD teleportation are not always zero when the entanglement falls to zero for a teleported state. This result clearly illustrates that in some cases we can only get a truly quantum teleportation by QD and SQD if we use a suitable field parameters and initial state, which have no entanglement. The results reveal that QD and SQD for teleported states are much robuster than entanglement in the process of communication. According to the results, the proposed scheme can greatly reduce the cost of quantum communication. We also obtain that the behaviour of the QD and SQD teleportation are similar to average fidelity. So, QD and SQD can be used to analyse teleported state as average fidelity.

Properties of Two Two-level Atoms Interacting with Intensity-Dependent Coupling

We discuss some new features of the model of two two-level atoms interacting with two single-mode thermal cavity field via multi-photon transitions under intensity-dependent coupling. We examine the dynamics of quantum and classical correlations of the system initially exists in Werner states. The results show that the sudden death and sudden birth of quantum entanglement occur but the geometric measure of quantum discord remains non-zero. It is observed that, by increasing the number of photons, the periods become shorter and the quantum discord and entanglement become irregular.

Dynamics of Quantum Correlation in de Sitter Spacetime

In this article, we investigate the dynamics of quantum correlation for two atoms interacting with massless scalar field in the background of de Sitter spacetime. We firstly derive the solving proc...

Quantum correlations dynamics of three-qubit states coupled to an XY spin chain: Role of coupling strengths☆☆Project supported by National Basic Research Program of China (Grant No. 2013CBA01702) and National Natural Science Foundation of China (Grant Nos. 61377016, 61575055, 10974039, 61307072, 61308017, and 61405056).

We investigate the prominent impacts of coupling strengths on the evolution of entanglement and quantum discord for a three-qubit system coupled to an XY spin-chain environment. In the case of a pure W state, more robust, even larger nonzero quantum correlations can be obtained by tailoring the coupling strengths between the qubits and the environment. For a mixed state consisting of the GHZ and W states, the dynamics of entanglement and quantum discord can characterize the critical point of quantum phase transition. Remarkably, a large nonzero quantum discord is generally retained, while the nonzero entanglement can only be obtained as the system-environment coupling satisfies certain conditions. We also find that the impact of each qubit’s coupling strength on the quantum correlation dynamics strongly depends on the variation schemes of the system-environment couplings.

Symmetry in the open-system dynamics of quantum correlations

We study the symmetry properties in the dynamics of quantum correlations for two-qubit systems in one-sided noisy channels, with respect to a switch in the location of noise from one qubit to the other. We consider four different channel types, namely depolarizing, amplitude damping, bit-flip, and bit-phase-flip channel, and identify the classes of initial states leading to symmetric decay of entanglement, non-locality and discord. Our results show that the symmetric decay of quantum correlations is not directly linked to the presence or absence of symmetry in the initial state, while it does depend on the type of correlation considered as well as on the type of noise. We prove that asymmetric decay can be used to infer, in certain cases, characteristic properties of the channel. We also show that the location of noise may lead to dramatic changes in the persistence of phenomena such as entanglement sudden death and time-invariant discord.

Quantum correlation of qubit-reservoir system in dissipative environments

In this work, the dynamics of quantum correlation (QC) in terms of geometric discord and its transfer coupled with dissipative reservoirs are investigated. Taken two canonical cases where the qubits of interest are initially prepared in extended Werner-like state and W-like states into account, we specifically reveal the dynamical behaviors of the geometric discord as each qubit locally interacts with its surrounding infinite degree-of-freedom reservoir. In the scenarios, the short-term and long-term dynamics of the geometric discord for the qubit- and reservoir-subsystem as well as its transfers between them are observed detailedly. It turns out that the geometric discord of qubit-subsystem decays asymptotically to zero while the counterpart of reservoir-subsystem can revive from time t = 0 to steady value, which sheds light on a transfer of the discord from the qubit-subsystem to the corresponding reservoir-subsystem.

Quantum Entanglement and Correlation of Two Qubit Atoms Interacting with the Coherent State Optical Field

Using the three criterions of the concurrence, the negative eigenvalue and the geometric quantum discord, we investigate the quantum entanglement and quantum correlation dynamics of two two-level atoms interacting with the coherent state optical field. We discuss the influence of different photon number of the mean square fluctuations on the temporal evolution of the concurrence, the negative eigenvalue and the geometric quantum discord between two atoms when the two atoms are initially in specific three states. The results show that different photon number of the mean square fluctuations can lead to different effects of quantum entanglement and quantum correlation dynamics.