Dynamics Of Quantum Entanglement Research Articles

Dissipative quantum entanglement dynamics of two and three qubits due to the dynamical Lamb effect

A theoretical framework to investigate the time evolution of the quantum entanglement due to the dynamical Lamb effect between $N$ superconducting qubits coupled to a coplanar waveguide in the presence of different sources of dissipation is developed. We quantitatively analyze the case of $N=2$ and $3$ qubits under the assumptions of single switching of the coupling and absence of dissipation within a perturbative approach. The same systems are analyzed for the general case of periodic switching of the coupling in the presence of dissipation via numerical calculations. Different measures of entanglement compatible with mixed states are adopted. It is demonstrated that the different measures show different level of details of the latter. The concurrence and the negativity are obtained in the two qubits case, the three-$\pi$ and the negativity in the three qubits case. It is shown that time-dependent Greenberger-Horne-Zeilinger states can be created even in presence of dissipation. To maximize the quantum entanglement between the qubits, the effects of tuning several parameters of the system are investigated.

Controlling of entropic uncertainty in open quantum system via proper placement of quantum register**Project supported by the National Natural Science Foundation of China (Grant Nos. 11264015 and 11404150).

We investigate the dynamical behaviors of quantum-memory-assisted entropic uncertainty and its lower bound in the amplitude-damping channel. The influences of different placement positions of the quantum register on the dynamics of quantum coherence, quantum entanglement, and quantum discord are analyzed in detail. The numerical simulation results show that the quantum register should be placed in the channel of the non-Markovian effect. This option is beneficial to reduce the entropic uncertainty and its lower bound. We also find that this choice does not change the evolution of the quantum coherence and quantum entanglement, but changes the dynamical process of the quantum discord of the system. These results show that quantum coherence, quantum entanglement, and quantum discord are different quantum resources with unique characteristics and properties, and quantum discord can play a key role in reducing the uncertainty of quantum systems.

Invariant entanglement and generation of quantum correlations under global dephasing

We investigate the dynamics of quantum entanglement and more general quantum correlations quantified via negativity and local quantum uncertainty, respectively, for two-qubit systems undergoing Markovian collective dephasing. Focusing on a two-parameter family of initial two-qubit density matrices, we study the relation of the emergence of the curious phenomenon of time-invariant entanglement and the dynamical behavior of local quantum uncertainty. Developing an illustrative geometric approach, we demonstrate the existence of distinct regions of quantum entanglement for the considered initial states and identify the region that allows for completely frozen entanglement throughout the dynamics, accompanied by generation of local quantum uncertainty. Furthermore, we present a systematic analysis of different dynamical behaviors of local quantum uncertainty, such as its sudden change or smooth amplification, in relation with the dynamics of entanglement.

Classical-driving-assisted coherence dynamics and its conservation**Project supported by the National Natural Science Foundation of China (Grant Nos. 61675115, 11204156, 11574178, and 11304179), the Science and Technology Plan Projects of Shandong University, China (Grant No. J16LJ52), and the Natural Science Foundation of Shandong Province, China (Grant No. ZR2016AP09).

We investigate the quantum coherence and quantum entanglement dynamics of a classical driven single atom coupled to a single-mode cavity. It is shown that the transformation between the atomic coherence and the atom-field entanglement exists, and can be improved by adjusting the classical driving field. The joint evolution of two identical single-body systems is also studied. The results show the quantum coherence transfers among composite subsystems, and the coherence conservation of composite subsystems is obtained. Moreover, the classical driving field can be used to suppress the decay of the coherence and entanglement, owing to considering the leaky cavity. The non-Markovian dynamics of the system is also discussed finally.

Robustness of Quantum Discord Between Two Noninteracting Qubits in Spin-Star Baths

We study the dynamics of quantum entanglement and discord between two noninteracting qubits, which couple with spin-star baths, obeying the XY Hamiltonian. We compare the dynamics of quantum discord with that of quantum entanglement. For the initial X-type state, in the common spin bath, the quantum discord is more robust than quantum entanglement. It is found that quantum discord of the two noninteracting qubits can be amplified, even in the regimes where entanglement suddenly disappears. This also points to a fact that the absence of entanglement does not necessarily indicate the absence of quantum correlations.

Quantum-entanglement pigeon-inspired optimization for unmanned aerial vehicle path planning

Purpose The purpose of this paper is to propose a new algorithm for independent navigation of unmanned aerial vehicle path planning with fast and stable performance, which is based on pigeon-inspired optimization (PIO) and quantum entanglement (QE) theory. Design/methodology/approach A biomimetic swarm intelligent optimization of PIO is inspired by the natural behavior of homing pigeons. In this paper, the model of QEPIO is devised according to the merging optimization of basic PIO algorithm and dynamics of QE in a two-qubit XXZ Heisenberg System. Findings Comparative experimental results with genetic algorithm, particle swarm optimization and traditional PIO algorithm are given to show the convergence velocity and robustness of our proposed QEPIO algorithm. Practical implications The QEPIO algorithm hold broad adoption prospects because of no reliance on INS, both on military affairs and market place. Originality/value This research is adopted to solve path planning problems with a new aspect of quantum effect applied in parameters designing for the model with the respective of unmanned aerial vehicle path planning.

Quantum coherence preservation of atom with a classical driving field under non-Markovian environment**Project supported by the National Natural Science Foundation of China (Grant Nos. 61675115, 11204156, 11574178, 11304179, and 11647172) and the Science and Technology Plan Projects of Shandong University, China (Grant No. J16LJ52).

The exact dynamics of an open quantum system consisting of one qubit driven by a classical driving field is investigated. Our attention is focused on the influences of single- and two-photon excitations on the dynamics of quantum coherence and quantum entanglement. It is shown that the atomic coherence can be improved or even maintained by the classical driving field, the non-Markovian effect, and the atom-reservoir detuning. The interconversion between the atomic coherence and the atom-reservoir entanglement exists and can be controlled by the appropriate conditions. The conservation of coherence for different partitions is explored, and the dynamics of a system with two-photon excitations is different from the case of single- photon excitation.

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.

Dynamics of quantum entanglement in quantum channels

Based on the von Neumann entropy, we give a computational formalism of the quantum entanglement dynamics in quantum channels, which can be applied to a general finite systems coupled with their environments in quantum channels. The quantum entanglement is invariant in the decoupled local unitary quantum channel, but it is variant in the non-local coupled unitary quantum channel. The numerical investigation for two examples, two-qubit and two-qutrit models, indicates that the quantum entanglement evolution in the quantum non-local coupling channel oscillates with the coupling strength and time, and depends on the quantum entanglement of the initial state. It implies that quantum information loses or gains when the state of systems evolves in the quantum non-local coupling channel.

Entropy, energy, and entanglement of localized states in bent triatomic molecules

The dynamics of quantum entropy, energy, and entanglement is studied for various initial states in an important spectroscopic Hamiltonian of bent triatomic molecules H2O, D2O, and H2S. The total quantum correlation is quantified in terms of the mutual information and the entanglement by the concurrence borrowed from the theory of quantum information. The Pauli entropy and the intramolecular energy usually used in the theory of molecules are calculated to establish a possible relationship between both theories. Sections of two quantities among these four quantities are introduced to visualize such relationship. Analytic and numerical simulations demonstrate that if an initial state is taken to be the stretch- or the bend-vibrationally localized state, the mutual information, the Pauli entropy, and the concurrence are dominant-positively correlated while they are dominantly anti-correlated with the interacting energy among three anharmonic vibrational modes. In particular, such correlation is more distinct for the localized state with high excitations in the bending mode. The nice quasi-periodicity of those quantities in D2O molecule reveals that this molecule prepared in the localized state in the stretching or the bending mode can be more appreciated for molecular quantum computation. However, the dynamical correlations of those quantities behave irregularly for the dislocalized states. Moreover, the hierarchy of the mutual information and the Pauli entropy is explicitly proved. Quantum entropy and energy in every vibrational mode are investigated. Thereby, the relation between bipartite and tripartite entanglements is discussed as well. Those are useful for the understanding of quantum correlations in high-dimensional states in polyatomic molecules from quantum information and intramolecular dynamics.

两纠缠二能级原子与单模光场相互作用的纠缠动力学过程研究

在光原子相互作用系统中，考虑两二能级原子间的偶极–偶极相互作用对原子间纠缠动力学过程的影响。研究表明：原子间的偶极–偶极相互作用对量子纠缠(共生纠缠度)动力学振荡过程具有抑制作用，当偶极–偶极相互为零时，量子纠缠呈双周期振荡效果，当偶极–偶极相互作用增强时，振荡频率逐渐降低，当偶极–偶极相互作用远大于原子与库环境相互作用强度时，量子纠缠呈明显的余弦振荡，其振荡频率为 。 The influence of dipole-dipole interactions between the two two-level entangled atoms for dynamics of quantum entanglement is studied in the system of matter-field interaction in quantum optics. The results show that the dipole-dipole interaction is capable to suppress dynamics of quantum entanglement (concurrence). If we have no regard for the dipole-dipole interaction, the dynamic of quantum entanglement is periodic oscillation including two different frequencies. Meanwhile, the frequency is decreasing with the increasing of the dipole-dipole interaction. When this interaction is much larger than that between the atoms and independent the single-mode field (modeled as extern environment), the process of dynamic of quantum entanglement is cosine oscillation with frequency .

Quantum Entanglement and Discord Dynamics of two Noninteracting Spin Qubits in Two Independent Spin Baths

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.

Entanglement Dynamics of Two Qubits Coupled Independently to Cavities in the Ultrastrong Coupling Regime: Analytical Results**Supported by the National Natural Science Foundation of China under Grant Nos 11174254 and 11474256.

Dynamics of quantum entanglement of two qubits in two identical quantum Rabi models is studied analytically in the framework of corrections to the rotating-wave approximations. A closed-form expression for the entanglement dynamics initiated from the well-known Bell states is derived, which is very close to the numerical exact results up to the ultrastrong coupling regime. It is found that the vanishing entanglement can be purely induced by the counter-rotating terms, and can be enhanced with the atom–cavity coupling.

Enhancing quantum entanglement by means of weak measurement under various environments

We investigate the relation between dissipation and coherent effects in the dynamics of quantum entanglement (QE) between two qubits by means of weak measurement. Under weak measurement, the increase or decrease of QE closely relates with the dissipation. The amplitude of QE will only be elevated through enhancing the measurement strength in weak correlated or no correlated instantaneous modes, and the entanglement sudden death (ESD) is retarded effectively. In the correlated dephasing mode, however, the amplitude of QE will decrease due to the increases of measurement strength. The periods for entanglement death, as well as the dark and bright in the concurrence are not changed. Therefore, the environmental relevance helps to enhance the amplitude of QE and delay the entanglement death.

Dynamics of nonlocality in an equidistance cavity coupled by fibers

Entanglement and nonlocality, two most striking features of quantum mechanics, are fundamental resources for quantum information processing. They play an important role in quantum information processing. Therefore, studying the dynamics of quantum nonlocality and entanglement is of importance for both fundamental research and practical applications. In this paper we consider the case that three identical two-level atoms are trapped respectively in the three separated equidistance single-mode cavities, which are placed at the vertices of an equilateral triangle and are coupled by three fibers. Each atom resonantly interacts with cavity via a one-photon hopping. The evolution of the state vector of the system is given by solving the schrodinger equation when the total excitation number of the system equals one. The dynamics of nonlocality in the system is investigated via Mermin-Ardehali-Belinksii-Klyshko (MABK) inequality. By the numerical calculations, the MABK inequality is studied when the initial state vector of three atoms is W state or the initial state vector of three cavities is also W state. The influence of cavity-fiber coupling constant on the MABK inequality is discussed. The evolution curves of the MABK parameters Ba and Bc are plotted. The curves show that Ba and Bc both display periodic oscillations, and their oscillation frequencies all increase with the increase of cavity-fiber coupling constant. Ba and Bc are both larger than 1 when the scaling time gt takes a certain value. The results show that the quantum state of three atoms or that of three cavities displays nonlocality. On the other hand, the nonlocality of three-atom quantum state is strengthened with the increase of cavity-fiber coupling constant.

Steady state quantum discord for circularly accelerated atoms

We study, in the framework of open quantum systems, the dynamics of quantum entanglement and quantum discord of two mutually independent circularly accelerated two-level atoms in interaction with a bath of fluctuating massless scalar fields in the Minkowski vacuum. We assume that the two atoms rotate synchronically with their separation perpendicular to the rotating plane. The time evolution of the quantum entanglement and quantum discord of the two-atom system is investigated. For a maximally entangled initial state, the entanglement measured by concurrence diminishes to zero within a finite time, while the quantum discord can either decrease monotonically to an asymptotic value or diminish to zero at first and then followed by a revival depending on whether the initial state is antisymmetric or symmetric. When both of the two atoms are initially excited, the generation of quantum entanglement shows a delayed feature, while quantum discord is created immediately. Remarkably, the quantum discord for such a circularly accelerated two-atom system takes a nonvanishing value in the steady state, and this is distinct from what happens in both the linear acceleration case and the case of static atoms immersed in a thermal bath.

The Dynamics of Quantum Entanglement and General Quantum Correlations in the Double Tavis-Cumming Model

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.

Entanglement and Energy for Vibrationally Localized States in Molecule CS2

The dynamics of quantum entanglement described by the von Neumann entropy is studied for the localized states of Fermi-resonance coupling vibrations in molecule CS2, where the interacting energy between the stretching and the bending modes is considered to establish a connection between entanglement and energy. It is shown that entanglement reveals dominant anti-correlation with the interacting energy for the stretch-localized state, while that exhibits dominantly positive correlation for the bend-localized state. The entanglement and the energy for the dislocalized states are discussed as well. Those are useful for molecular quantum computing and quantum information in high dimensional states.

Discord and entanglement of two-particle quantum walk on cycle graphs

In this paper, we investigate the dynamics of quantum discord and entanglement between the coin states of two quantum walkers on cycle graphs of various size in discrete time. For a few special cycle sizes, we obtained analytical solutions showing the origin of perfect periodic recurrence of quantum discord and entanglement. We found that the time evolution of such quantum correlations becomes increasingly complex when we introduce local interactions between the two walkers by applying an additional phase to the coin operator when they are at the same node. The effects of the interaction strength on the dynamics of the quantum discord and entanglement are studied in detail.

Probing the quantum entanglement under finite temperature environment in nonineritial frames

In this paper, we investigate the dynamics of quantum entanglement of a two-qubit quantum system coupled with generalized amplitude damping (GAD) channel of nonzero temperature in noninertial frames. The results show that the concurrence decreases with the increase of acceleration and channel parameter r has a decisive impact on the entanglement. Accidentally, we manifest the inequivalence of the quantization for a Dirac field under the GAD channel in the noninertial frames.