Disentanglement Time Research Articles

Speed of Evolution and Correlations in Multi-Mode Bosonic Systems.

We employ an exact solution of the thermal bath Lindblad master equation with the Liouvillian superoperator that takes into account both dynamic and environment-induced intermode couplings to study the speed of evolution and quantum speed limit (QSL) times of a open multi-mode bosonic system. The time-dependent QSL times are defined from quantum speed limits, giving upper bounds on the rate of change of two different measures of distinguishability: the fidelity of evolution and the Hilbert-Schmidt distance. For Gaussian states, we derive explicit expressions for the evolution speed and the QSL times. General analytical results are applied to the special case of a two-mode system where the intermode couplings can be characterized by two intermode coupling vectors: the frequency vector and the relaxation rate vector. For the system initially prepared in a two-mode squeezed state, dynamical regimes are generally determined by the intermode coupling vectors, the squeezing parameter and temperature. When the vectors are parallel, different regimes may be associated with the disentanglement time, which is found to be an increasing (a decreasing) function of the length of the relaxation vector when the squeezing parameter is below (above) its temperature-dependent critical value. Alternatively, we study dynamical regimes related to the long-time asymptotic behavior of the QSL times, which is characterized by linear time dependence with the proportionality coefficients defined as the long-time asymptotic ratios. These coefficients are evaluated as a function of the squeezing parameter at varying temperatures and relaxation vector lengths. We also discuss how the magnitude and orientation of the intermode coupling vectors influence the maximum speed of evolution and dynamics of the entropy and the mutual information.

Dynamics of entangled pair of spin-1/2 particles under independent random magnetic fields

The dynamics of a pair of spatially separated spin-1/2 particles which are initially entangled and subjected to independent random magnetic fields is obtained by considering a pure joint state of entangled spin-1/2 particles and using stochastic calculus. The disentanglement time defined as the time taken for the particles to become disentangled, is obtained from the dynamics. In view of entanglement-based quantum communication, this analysis could help to assess the feasibility to send and receive quantum information within the disentanglement time.

Lindblad Dynamics and Disentanglement in Multi-Mode Bosonic Systems.

In this paper, we consider the thermal bath Lindblad master equation to describe the quantum nonunitary dynamics of quantum states in a multi-mode bosonic system. For the two-mode bosonic system interacting with an environment, we analyse how both the coupling between the modes and the coupling with the environment characterised by the frequency and the relaxation rate vectors affect dynamics of the entanglement. We discuss how the revivals of entanglement can be induced by the dynamic coupling between the different modes. For the system, initially prepared in a two-mode squeezed state, we find the logarithmic negativity as defined by the magnitude and orientation of the frequency and the relaxation rate vectors. We show that, in the regime of finite-time disentanglement, reorientation of the relaxation rate vector may significantly increase the time of disentanglement.

The dynamics of tripartite quantum correlations under Ornstein–Uhlenbeck noise

The dynamics of the tripartite thermal entanglement measured by Negativity (N) and the tripartite quantum correlation described by measurement-induced disturbance (MID) under Ornstein–Uhlenbeck noise are investigated. This study has found that the tripartite N and MID can be preserved more effectively in the non-Markovian environment than in the short-time limit and the Markov limit cases. The short-time limit is a better approximation than the Markov limit. MID vanishes only in the asymptotic limit, while entanglement sudden death may occur, and the decreasing duration of MID far outweighs entanglement. This implies that MID is more robust than Negativity. As the noise bandwidth increases, the disentanglement time and the decay time of MID are significantly shorter. The increase of XZX[Formula: see text]+[Formula: see text]YZY three-site interaction is more effective than XZY−YZX three-site interaction to enhance Negativity and MID as well as the disentanglement time. The magnetic field diminishes Negativity and MID, but has no significant influence on the decreasing durations of both Negativity and MID.

Properties of hybrid entanglement among two flux qubits and a nitrogen-vacancy-center ensemble

We investigate hybrid flux-nitrogen-vacancy (NV) entanglement in the system consisting of two flux qubits and an NV-center ensemble (NVE). The influence of the initial entanglement degree of the flux qubit C, the coupling strength between two flux qubits, the coupling strength between the flux qubit M and the NVE on the bipartite entanglement and the tripartite entanglement is discussed. The maximally bipartite entangled state and the maximally tripartite entangled state can be obtained under certain conditions. In addition, it is shown that the time of disentanglement of the hybrid quantum system can be controlled by adjusting the coupling strength between two flux qubits and the coupling strength between the flux qubit M and the NVE.

Entanglement loss in molecular quantum-dot qubits due to interaction with the environment

We study quantum entanglement loss due to environmental interaction in a condensed matter system with a complex geometry relevant to recent proposals for computing with single electrons at the nanoscale. We consider a system consisting of two qubits, each realized by an electron in a double quantum dot, which are initially in an entangled Bell state. The qubits are widely separated and each interacts with its own environment. The environment for each is modeled by surrounding double quantum dots placed at random positions with random orientations. We calculate the unitary evolution of the joint system and environment. The global state remains pure throughout. We examine the time dependence of the expectation value of the bipartite Clauser–Horne–Shimony–Holt (CHSH) and Brukner–Paunković–Rudolph–Vedral (BPRV) Bell operators and explore the emergence of correlations consistent with local realism. Though the details of this transition depend on the specific environmental geometry, we show how the results can be mapped on to a universal behavior with appropriate scaling. We determine the relevant disentanglement times based on realistic physical parameters for molecular double-dots.

Disentanglement Dynamics of a Data Driven Quantum Neural Network

This study examines the disentanglement evolution of a quantum neural network (QNN) model locally in contact with data environments. As a valuable resource, duration of entanglement in quantum systems is extremely significant. Therefore, the effect of various initial states to the generation or decay of entanglement has been investigated under pure and maximally mixed environmental states as two limit cases. Numerical results show that initial state preparation has a profound impact on the fate of entanglement even in the course of maximally noisy environments. The obtained results reveal that the decay of entanglement of the quantum neural network (with flip-flop type interaction) is affected by the initial preparation of the Bell state even in the presence of pure state environmental monitoring. Depending on the results it’s also suggested to begin with coherent product states since it provides robust entanglement generation with longer disentanglement time during the open quantum system evolution.

Dynamics of Bell-nonlocality and entanglement in a ring cavity induced by spontaneous emission

By considering the spatial motion of the atoms, we study the time evolution of Bell nonlocality and entanglement of a pair of atoms for two kinds of Werner-type internal states in an ideal single-mode ring cavity. We have proved that both Bell nonlocality and entanglement have the phenomena of sudden death and sudden birth for the initial state W±′, while for the initial state W±, Bell nonlocality has the phenomenon of sudden death, but entanglement decays to zero asymptotically over time. We also notice that the preservation of Bell-inequality violation is much shorter than that of entanglement. In addition, it is shown that the disentanglement time and the Bell-inequality violation time both depend on the purity and the width of the wave packet describing the motion of the atomic center of mass.

Competition between phase transition and thermophoretic expansion of a transient poly(N-isopropylacrylamide) network.

Aqueous solutions of highly entangled ultra-high molar mass ( 2.4×106 g/mol) poly(N-isopropylacrylamide) (PNIPAM) have been subjected to an inhomogeneous temperature field by selective heating of a single embedded gold nanoparticle (GNP) by means of a focused laser beam. Randomly distributed tracer GNPs are trapped in the meshes of the transient entanglement network and serve as tracers for the monitoring of the network deformation field. Because of the positive Soret coefficient of PNIPAM in water, the viscoelastic polymer network is expanded by thermophoretic forces pointing away from the hot center. Close to the heated GNP the thermoresponsive polymer solution crosses the binodal and the network contracts, which is made visible by an inward motion of tracer GNPs, which are randomly embedded in the polymer network and not illuminated by the laser beam. Within a thin transition zone the network contraction and the competing thermophoretic network expansion cancel out in the steady state. There is, however, no cancellation during the transients due to the different time scales of both mechanisms. The network within the crossover region first undergoes an expansion that is followed by a slower contraction. From the global expansion and contraction, the local strain (stretching and compression) of the transient network can be calculated. Due to the long disentanglement times, corresponding to long lifetimes of the meshes of the network, the whole process is fully reversible.

Control and Transfer of Entanglement between Two Atoms Driven by Classical Fields under Dressed-State Representation**Supported by National Natural Science Foundation of China under Grant Nos. 11247213, 61368002, 11304010, 11264030, 61168001, China Postdoctoral Science Foundation under Grant No. 2013M531558, Jiangxi Postdoctoral Research Project under Grant No. 2013KY33, the Natural Science Foundation of Jiangxi Province under Grant No. 20142BAB217001, the Foundation for

We have studied the dynamics and transfer of the entanglement of the two identical atoms simultaneously interacting with vacuum field by employing the dressed-state representation. The two atoms are driven by classical fields. The influence of the initial entanglement degree of two atoms, the coupling strength between the atom and the classical field and the detuning between the atomic transition frequency and the frequency of classical field on the entanglement and atomic linear entropy is discussed. The initial entanglement of the two atoms can be transferred into the entanglement between the atom and cavity field when the dissipation is neglected. The maximally entangled state between the atoms and cavity field can be obtained under some certain conditions. The time of disentanglement of two atoms can be controlled and manipulated by adjusting the detuning and classical driving fields. Moreover, the larger the cavity decay rate is, the more quickly the entanglement of the two atoms decays.

The relevance of molecular weight in the design of amorphous biodegradable polymers with optimized shape memory effect

The shape memory effect (SME) has long been the focus of interest of many research groups that have studied many facets of it, yet to the authors’ knowledge some molecular parameters, such as the molecular weight, have been skipped. Thus, the aim of this work is to offer further insight into the shape memory effect, by disclosing the importance of the molecular weight as the relevant parameter dictating the extension of the rubbery plateau, which is the scenario where the entropic network of entanglements manifests. For this, a set of biodegradable amorphous poly(rac-d,l)lactides have been synthesised by ring opening copolymerization of a racemic mixture of L-and D-lactide. The analysis performed on the synthesised enantiomeric copolylactides includes the determination of molecular weights by means of Gel Permeation Chromatography (GPC), thermal properties by Differential Scanning Calorimetry (DSC), dynamic mechanical analysis (DMA) and rheological tests using small amplitude oscillatory flow analysis. Shape memory properties have been determined by means of specific cyclic thermo-mechanic test protocol. It has been shown that the recovery capacity of amorphous PDLLA is linked to the disentanglement time through an exponential law.

Polyacrylonitrile solution homogeneity study by dynamic shear rheology and the effect on the carbon fiber tensile strength

Poly(acrylonitrile‐co‐methacrylic acid) (PAN‐co‐MAA)/N,N‐dimethylformamide (DMF) solutions were prepared and dynamic shear rheology of these solutions were investigated. With increasing stirring time up to 72 h at 70°C, the polymer solution became less elastic (more liquid‐like) with a ∼60% reduction in the zero‐shear viscosity. Relaxation spectra of the PAN‐co‐MAA/DMF solutions yield a decrease in relaxation time (disentanglement time, τd), corresponding to an about 8% decrease in viscosity average molecular weight. The log‐log plot of G′ (storage modulus) versus G″ (loss modulus) exhibited an increase in slope as a function of stirring time, suggesting that the molecular level solution homogeneity increased. In order to study the effect of solution homogeneity on the resulting carbon fiber tensile strength, multiple PAN‐co‐MAA/DMF solutions were prepared, and the precursor fibers were processed using gel‐spinning, followed by continuous stabilization and carbonization. The rheological properties of each solution were also measured and correlated with the tensile strength values of the carbon fibers. It was observed that with increasing the slope of the G′ versus G″ log‐log plot from 1.471 to 1.552, and reducing interfilament fiber friction during precursor fiber drawing through the addition of a fiber washing step prior to fiber drawing, the carbon fiber strength was improved (from 3.7 to 5.8 GPa). This suggests that along with precursor fiber manufacturing and carbonization, the solution homogeneity is also very important to obtain high strength carbon fiber. POLYM. ENG. SCI., 56:361–370, 2016. © 2016 Society of Plastics Engineers

QUANTUM COMPUTATIONS AND ATOM-FIELD ENTANGLED STATES IN JAYNES-CUMMINGS GENERALIZED MODEL

Atom-field entanglement in two-atom system in different initial states in Jay-nes-Cummings model with degenerate two photon transition with dependant from intensity of the field of parameter of atom-field interaction is considered. It is shown that consideration of discontency of parameter of atom-field interaction for some initial states of atoms leads to damping or collapse of instant death of entanglement effect and changes of disentanglement time.

Dependence of noise induced effects on state preparation in multiqubit systems

Abstract The perturbation of multiqubit systems by an external noise can induce various effects like decoherence, stochastic resonance and anti-resonance, and noise-shielding. We investigate how the appearance of these effects on disentanglement time depends on the initial preparation of the systems. We present results for 2-, 3- and 4-qubit chains in various arrangements and observe a clear dependence on the combination of initial geometry of the state space and the placement of noise. Finally, we see that temperature can play a constructive role for the control of these noise induced effects.

Photothermal Deformation of a Transient Polymer Network

Gold nanoparticles (GNPs) are embedded in a highly entangled solution of an ultrahigh molar mass polymer (polystyrene Mw = 16 800 kg/mol in toluene). When an isolated GNP is heated by a focused laser beam, the solvent is attracted to and the polymer is pushed away from the particle surface by thermophoretic forces, thereby elastically deforming the transient polymer network. Because of the long disentanglement time, the randomly distributed GNPs are trapped in the meshes of the transient polymer network and allow for a visual observation of the network deformation field using an optical microscope. The observed displacement field of the meshes is of long-ranged nature and only limited by the finite size of the cuvette, despite of the local heating of a single submicrometer-sized GNP.

Quantum correlation dynamics of two two-level atoms in common environment

By exactly solving the model of two two-level atoms with dipole-dipole interaction, interacting with a common environment, quantum entanglement and quantum discord of two atoms are obtained. In this paper, the influences of the non-Markovian effect of environment, the dipole-dipole interaction of two atoms and the detunings of the central frequency of the cavity and the transition frequency of the atoms on quantum entanglement and quantum discord dynamics of two atoms are comprehensively considered. The study shows that in the non-Markovian regime and the resonant case, if two atoms are initially in the entangled state, the damping of quantum entanglement and quantum discord will be remarkably suppressed. More specially, in the off-resonant case, the disentanglement time of the two atoms can be considerably prolonged. On the other hand, if two atoms are initially in the separable state, the dipole-dipole interaction can enhance the amplitude of oscillations of quantum entanglement and quantum discord in a short time, but the steady values of quantum entanglement and quantum discord cannot be changed by the dipole-dipole interaction in the long-time limit. Finally, the different influences of the dipole-dipole interaction on quantum entanglement and quantum discord also are discussed.

Statistical portrait of the entanglement decay of two-qubit memories

We present a novel approach to the study of entanglement decay, which focuses on collective properties. As an example, we investigate the entanglement decay of a two-qubit system, produced by local identical reservoirs acting on the qubits, for three experimentally and theoretically relevant cases. We study the probability distributions of disentanglement times, a quantity independent of the measure used to quantify entanglement, and the time-dependent probability distribution of concurrence. Analytical results are obtained for initially uniformly distributed pure states. The calculation of these probability distributions gives a complete insight on how different decoherence channels affect the entanglement initially contained in the set of two-qubit pure states. Numerical results are reported for randomly distributed initial mixed states. Although the paper focuses in Markovian noisy channels, we show that our results also describe non-autonomous and non-Markovian channels.

Entanglement for two-atom Tavis–Cummings model with degenerate two-photon transitions in the presence of the Stark shift

The dynamics of atom–field entanglement for two two-level atoms with degenerate two-photon transitions interacting with one-mode radiation field with taking into account the Stark shift is investigated. Asymptotic solutions for system state vectors are obtained in the approximation of large initial coherent fields. The atom–field entanglement is investigated also on the basis of the linear atomic entropy dynamics. The possibility of the system being initially in a pure disentangled state to revive into this state during the evolution process is shown. Conditions and times of disentanglement are derived.

STOCHASTIC ANTI-RESONANCE IN THE TIME EVOLUTION OF INTERACTING QUBITS

We investigate the possibility of appearance of new phenomena derived from the influence of noise on quantum systems. As a starting point we study the entanglement evolution of two coupled qubits in interaction with an external environment and in the presence of an external magnetic field with a stochastic component. The results show the expected degradation of entanglement due to the noise. The new effect is that for particular initial states the time of disentanglement depends in a non-monotonous way on the strength of the noise. We find that it is shortest for an intermediate strength value of the noise. This we call "stochastic anti-resonance." Our new result indicates that there are noise values which are particularly harmful and should be avoided. This could lead to a better understanding of noisy perturbations and their role for optimal designing of quantum devices.

Manipulating the Sudden Death of Entanglement in Two-qubit Atomic Systems

We investigate the entanglement dynamics of a general two-qubit system in a noisy environment presenting analytical descriptions of the time evolution of entanglement having some unitary operations after its evolution in dissipative environments. We show that quantum gates (unitary operators) and bath switching can change the subsequent dynamics of entanglement. For this purpose, we consider x and bath switching operations that change the disentanglement time from finite to infinite.