Coherent Behavior Research Articles

Investigation of n-type gallium nitride grating for applications in coherent thermal sources

In this study, polarized reflection and emission spectroscopy was employed in order to describe experimentally and numerically the coherent behavior of surface plasmon phonon polaritons in shallow n-type gallium nitride grating. For the grating with a 1 μm depth and an 11 μm period, polariton coherence was observed measuring the reduction of the linewidth and the redshift of the resonance position in both reflection and emission spectra with the increase in the incident angle. Maximum coherence conditions were found at a frequency of 562 cm−1 and an angle of 37°, demonstrating the coherence length value up to 724 μm (41λ).

Analysis and modeling of ground motion coherency at uniform site conditions

In this work, nonstationary ground motion coherency analysis and modeling are performed using wavelet analysis and relevance vector machine regression. Earthquake ground motion data from four events recorded at dense seismograph SMART-1 array in north-south and east-west horizontal directions are used to investigate the lagged coherency behavior. Wavelet transform is used to compute the nonstationary lagged coherency that characterizes the space-time variation of seismic ground motion. Lagged coherency behavior with frequency, distance, and time is examined. It is shown that the lagged coherency is a time-varying quantity. The results implied that the lagged coherency on uniform soil is relatively insensitive to the earthquake events, and depends mainly on time, frequency, and separation distance. Relevance Vector Machines (RVM) regression is used to develop a model for nonstationary lagged coherency that characterizes the space-time variation of seismic ground motion. Earthquake ground motion in the in the north-south and the first principal directions is used to determine the lagged coherency model. The proposed model does not require a fixed parametric functional form. The developed model can estimate the lagged coherency for different separation distances at different time instants and frequencies.

Waiting Time Distributions of Transport through a Two-Channel Quantum System

In this work, the waiting time distribution (WTD) statistics of electron transport through a two-channel quantum system in a strong Coulomb blockade regime and non-interacting dots are investigated by employing a particle-number resolved master equation with the Born–Markov approximation. The results show that the phase difference between the two channels, the asymmetry of the dot-state couplings to the left and right electrodes, and Coulomb repulsion have obvious effects on the WTD statistics of the system. In a certain parameter range, the system manifests the coherent oscillatory behavior of WTDs in the strong Coulomb blockade regime, and the phase difference between the two channels is clearly reflected in the oscillation phase of the WTDs. The two-channel quantum dot (QD) system for non-interacting dots manifests nonrenewal characteristics, and the electron waiting time of the system is negatively correlated. The different phase differences between the two channels can clearly enhance the negative correlation. These results deepen our understanding of the WTD statistical properties of electron transport through a mesoscopic QD system and help pave a new path toward constructing nanostructured QD electronic devices.

Quantum information processing and quantum optics with circuit quantum electrodynamics

Since the first observation of coherent quantum behaviour in a superconducting qubit, now more than 20 years ago, there have been substantial developments in the field of superconducting quantum circuits. One such advance is the introduction of the concepts of cavity quantum electrodynamics (QED) to superconducting circuits, to yield what is now known as circuit QED. This approach realizes in a single architecture the essential requirements for quantum computation, and has already been used to run simple quantum algorithms and to operate tens of superconducting qubits simultaneously. For these reasons, circuit QED is one of the leading architectures for quantum computation. In parallel to these advances towards quantum information processing, circuit QED offers new opportunities for the exploration of the rich physics of quantum optics in novel parameter regimes in which strongly nonlinear effects are readily visible at the level of individual microwave photons. We review circuit QED in the context of quantum information processing and quantum optics, and discuss some of the challenges on the road towards scalable quantum computation. The introduction of concepts from cavity quantum electrodynamics to superconducting circuits yielded circuit quantum electrodynamics, a platform eminently suitable to quantum information processing and for the exploration of novel regimes in quantum optics.

Wave-particle duality employing quantum coherence in superposition with non-orthogonal pointers

We propose the notion of quantum coherence for superpositions over states which are not necessarily mutually orthogonal. This anticipatedly leads to a resource theory of non-orthogonal coherence. We characterize free states and free operations in this theory, and connect the latter with free operations in the resource theory of quantum coherence for orthogonal bases. We show that the concept of non-orthogonal coherence naturally furnishes us with a wave-particle duality in quantum double-slit experiments where the channels beyond the slits are leaky between them. Furthermore, we demonstrate existence of a unique maximally coherent qubit state corresponding to any given purity. In addition, and in contradistinction with the case of orthogonal bases, there appears a non-trivial minimally coherent qubit state for a given purity. We also study the behavior of quantum coherence for some typical configurations of non-orthogonal bases which have no analogs for orthogonal bases. We further investigate the problem of determining the energy cost of creating non-orthogonal coherence, and find that it scales linearly with the non-orthogonal coherence created.

Motor learning and COMT Val158met polymorphism: Analyses of oculomotor behavior and corticocortical communication.

Differences in motor learning can be partially explained by differences in genotype. The catechol-O-methyltransferase (COMT) Val158Met polymorphism regulates the dopamine (DA) availability in the prefrontal cortex modulating motor learning and performance. Given the differences in tonic and phasic DA transmission, this study aimed to investigate whether the greater cognitive flexibility associated with the Val allele would favor the learning of movement parametrization, while the greater cognitive stability associated with the Met allele favors the acquisition of the movement pattern. Furthermore, we investigated if the genotypic characteristics impact visual scanning of information related to parametrization and to the movement pattern, and the level of cortical connectivity associated with motor planning and control. Performance and learning of a sequential motor task were compared among three genotypes (Val/Val, Val/Met, and Met/Met), as well as their oculomotor behavior and level of cortical coherence. The findings show that the cognitive flexibility promoted by the Val allele is associated with a better parametrization. The search for information through visual scanning was specific to each genotype. Also, a greater cortical connectivity associated with the Val allele was found. The combined study of behavioral, electrophysiological and molecular levels of analysis showed that the cognitive stability and flexibility associated with the COMT alleles, influence specific aspects of motor learning.

Adaptive Learning: A New Decentralized Reinforcement Learning Approach for Cooperative Multiagent Systems

Multiagent systems (MASs) have received extensive attention in a variety of domains, such as robotics and distributed control. This paper focuses on how independent learners (ILs, structures used in decentralized reinforcement learning) decide on their individual behaviors to achieve coherent joint behavior. To date, Reinforcement learning(RL) approaches for ILs have not guaranteed convergence to the optimal joint policy in scenarios in which communication is difficult. Especially in a decentralized algorithm, the proportion of credit for a single agent’s action in a multiagent system is not distinguished, which can lead to miscoordination of joint actions. Therefore, it is highly significant to study the mechanisms of coordination between agents in MASs. Most previous coordination mechanisms have been carried out by modeling the communication mechanism and other agent policies. These methods are applicable only to a particular system, so such algorithms do not offer generalizability, especially when there are dozens or more agents. Therefore, this paper mainly focuses on the MAS contains more than a dozen agents. By combining the method of parallel computation, the experimental environment is closer to the application scene. By studying the paradigm of centralized training and decentralized execution(CTDE), a multi-agent reinforcement learning algorithm for implicit coordination based on TD error is proposed. The new algorithm can dynamically adjust the learning rate by deeply analyzing the dissonance problem in the matrix game and combining it with a multiagent environment. By adjusting the dynamic learning rate between agents, coordination of the agents’ strategies can be achieved. Experimental results show that the proposed algorithm can effectively improve the coordination ability of a MAS. Moreover, the variance of the training results is more stable than that of the hysteretic Q learning(HQL) algorithm. Hence, the problem of miscoordination in a MAS can be avoided to some extent without additional communication. Our work provides a new way to solve the miscoordination problem for reinforcement learning algorithms in the scale of dozens or more number of agents. As a new IL structure algorithm, our results should be extended and further studied.

Dynamic phase fluctuations in potential-driven Bose–Einstein condensate

We report on the dynamics of a Bose–Einstein condensate in one and two dimensions driven by the time-dependent harmonic trapping potential. Without the inter-particle interaction, the condensate exhibits the coherent behavior with the time-oscillating density distribution. When the inter-particle interaction is taken into consideration, the phase fluctuations, the multi-peak structure of the density distribution, and the coherence revival phenomenon, apart from the well-studied density oscillation behavior, can be observed in the condensate. Furthermore, it is demonstrated that due to the dimensional restriction these effects are more stable in the two and three-dimensional system, if compared to the one-dimensional case.

Coherent magnetic behaviors of bcc FexMn1−x films on MgO (0 0 1)

We report the epitaxial growth, structural characterization, magnetic and transport properties of body-centered-cubic (bcc) FexMn1−x films on MgO (0 0 1). Reflection high-energy electron diffraction and high-resolution x-ray diffractometry show that the 15-nm-thick FexMn1−x films remain pure bcc when x ≥ 0.71. A secondary phase appears when x ≤ 0.69. The moments of the pure bcc films are found no deviation from the Slater-Pauling behavior, much beyond the reported range of x ≥ 0.84. A dramatic moment deviation occurs with a secondary phase observed. The transport results exhibit a coherent magnetic behavior of the bcc FexMn1−x films up to x = 0.71 (29% Mn).

Quantum Beat between Sunlight and Single Photons.

We demonstrate fourth-order quantum beat between sunlight and single photons from a quantum dot. With a fast time-resolved detection system, we observed high-visibility quantum beat between the independent photons of different frequencies from the two astronomically separated light sources. The temporal dynamics of the beat oscillation indicate the coherent behavior of the interfering photons, and the raw visibility of two-photon interference shows violation of the classical limit with a frequency mismatch of three-times the line width.

Superdirectional light emission and emission reversal from microcavity arrays

Optical microdisk cavities with certain asymmetric shapes are known to possess unidirectional far-field emission properties. Here, we investigate arrays of these dielectric microresonators with respect to their emission properties resulting from the coherent behaviour of the coupled constituents. This approach is inspired by electronic mesoscopic physics where the additional interference effects are known to enhance the properties of the individual system. As an example we study the linear arrangement of nominally identical Lima\c{c}on-shaped cavities and find mostly an increase of the portion of directional emitted light while its angular spread is largely diminished from 20 degrees for the single cavity to about 3 degrees for a linear array of 10 Lima\c{c}on resonators, in fair agreement with a simple array model. Moreover, by varying the inter-cavity distance we observe windows of reversion of the emission directionality and super-directionality that can be interesting for applications. We introduce a generalized array factor model that takes the coupling into account.

Entropy squeezing and coherence for a non-Markovian dissipative qubit system

We examine the impact of the non-Markovian environment on the dynamical behavior of the quantum coherence and entropy squeezing considering a two-level atomic system (qubit) immersed in a reservoir with zero-temperature for two types of non-Markovian environments. We consider a cavity little off-resonance with the transition frequency of the qubit and the case of a non-perfect photonic band gap (PBG). We show that the amount of coherence is dependent on the structure of the environment and influenced through the memory effects. We obtain that the delay and revival of the coherence loss might take place by controlling the detuning of the cavity-qubit system. Whereas, a partial coherence trapping occurs in non-ideal PBG and the decrease of the gap width will destroy the coherence. On the other hand, we show the situation for which the squeezing is occurring and enhanced with respect to the main parameters for the system. Finally, we display the monotonic dependence of the quantum coherence and squeezing on the main model parameters.

Two-dimensional hybrid-direct kinetic simulation of a Hall thruster discharge plasma

A direct kinetic (DK) simulation is capable of modeling the nonequilibrium state of plasma as it evolves in the discharge region of a Hall thruster without the numerical noise that is inherent to particle-based methods since the velocity distribution functions are obtained in a deterministic manner. In this work, a hybrid-DK simulation utilizes a quasi-one-dimensional fluid electron model in conjunction with a two-dimensional DK method to simulate neutral atoms and ions in a Hall thruster channel and near-field plume. Instantaneous and time-averaged plasma properties calculated using the hybrid-DK simulation are benchmarked against the results obtained from a two-dimensional hybrid-particle-in-cell (PIC) simulation with an identical fluid electron model. For both high and low-frequency oscillations, the two simulations show good agreement for time-averaged and dynamic plasma properties. Numerical noise tends to randomize plasma oscillations in the PIC simulation results, whereas the DK results exhibit coherent oscillatory behavior.

Coherent vs incoherent effects and Debye length

For some class of studies, the space charge is treated as frozen, allowing to capture the dynamics of incoherent phenomena. We explore the possibility that a beam may exhibit non-resonant coherent behavior by developing and studying a one-dimensional model.

Leisure behavior and sense of coherence in the context of depression.

Improved sense of coherence (SOC) can protect health among individuals with depression. Literature suggests that leisure behavior can improve SOC, yet empirical studies are lacking. The current study aimed to examine whether leisure behavior was associated with SOC and depression. A cross-sectional online survey method was used with a sample of community-living adults (62% female, age 18-75 years) with a self-reported current or historical diagnosis of depression recruited from four different depression-related populations. The results of structural equation modeling found that leisure behavior predicted greater SOC as well as lower depressive symptoms. Greater SOC was associated with lower perceived stress and lower depressive symptoms. The total effect size, including both direct and indirect association between leisure behavior and depressive symptoms was 0.452. The findings suggested the potential benefits of leisure behavior on SOC and depressive symptoms.

Multipartite quantum discord and quantum coherence in Heisenberg–Ising bond alternating chain

The behaviour of multipartite quantum discord and quantum coherence in Heisenberg–Ising bond alternating spin-1 / 2 chain are computed by exploiting the method of quantum renormalisation group (QRG). At larger number of iterations, both quantum coherence and quantum discord have found to exhibit quantum phase transition (QPT) between the spin fluid phase and the Neel phase. In addition, at the critical point, the first derivative of both quantum coherence and quantum discord have shown a non-analytical behaviour. Finally, the scaling behaviour of both quantum coherence and quantum discord has been investigated.

The dynamical behavior of quantum coherence in one-dimensional transverse-field Ising model

Quantum coherence and quantum correlation, as a key feature, have proven essential to our understanding of quantum critical phenomena. In this study, we contribute to characterize the quantum phase transition in the Ising model in a transverse field by using l1 norm coherence and quantum discord. The unitary operator is enforced in the model so that we extend the static problem to dynamics case. For quantum coherence, we show that it oscillates with the increase of magnetic field g. The extent of oscillation decreases when the size of the spin chain increase. Meanwhile, however, the oscillating frequency will increase. For quantum discord, it will decrease with the increase of quantum renormalization group and that result totally different with quantum coherence. We demonstrate that the classical correlation have similar behavior like quantum coherence. Furthermore, we show that quantum coherence also can detect the quantum critical point even when the intrinsic decoherence are enforced in the model.

TRÂNSITO E EDUCAÇÃO: conceitos e práticas desenvolvidas com alunos do ensino básico em Ituiutaba (MG) no ano de 2018

Traffic is visible to human perceptions, because of this a concern about daily occurrences occurring throughout the country becomes essential. Several reasons may stimulate a traffic accident, such as driver recklessness, lack of knowledge about traffic laws, dangerous driving, as well as other associations. In the face of the case, a greater intensification on the subject is necessary, including applying the Tijucana community to which it was the target of the research, transforming the lack of information into an alert, consequently passing the learning to the next. In this sense, the main objective of this research was to present experiences obtained with the students of the CAIC (Center for Integrated Community Service) in Ituiutaba-MG, regarding the usual subjects on traffic and education, with the purpose of establishing a more playful dialogue, coherent behavior towards the situations that are experienced daily in traffic. The methodological processes that guided this research were divided in some stages: a) Bibliographic Review; b) Data collection; c) Reambulation at school; d) Sample of the project at UFU (Federal University of Uberlândia - Campus Pontal) and final wording. It is worth highlighting that the results attracted were notorious, thanks to the collaboration of those involved, emphasizing important aspects about traffic education, as well as the establishment of dialogue and awareness on the part of elementary school students in relation to the topic discussed, so that effective actions of can be really applied in your daily life, in a functional and conscious way.

Assessing the quantumness of the annealing dynamics via Leggett Garg\u2019s inequalities: a weak measurement approach

Adiabatic quantum computation (AQC) is a promising counterpart of universal quantum computation, based on the key concept of quantum annealing (QA). QA is claimed to be at the basis of commercial quantum computers and benefits from the fact that the detrimental role of decoherence and dephasing seems to have poor impact on the annealing towards the ground state. While many papers show interesting optimization results with a sizable number of qubits, a clear evidence of a full quantum coherent behavior during the whole annealing procedure is still lacking. In this paper we show that quantum non-demolition (weak) measurements of Leggett Garg inequalities can be used to efficiently assess the quantumness of the QA procedure. Numerical simulations based on a weak coupling Lindblad approach are compared with classical Langevin simulations to support our statements.

Coherent collective behaviour emerging from decentralised balancing of social feedback and noise

Decentralised systems composed of a large number of locally interacting agents often rely on coherent behaviour to execute coordinated tasks. Agents cooperate to reach a coherent collective behaviour by aligning their individual behaviour to the one of their neighbours. However, system noise, determined by factors such as individual exploration or errors, hampers and reduces collective coherence. The possibility to overcome noise and reach collective coherence is determined by the strength of social feedback, i.e. the number of communication links. On the one hand, scarce social feedback may lead to a noise-driven system and consequently incoherent behaviour within the group. On the other hand, excessively strong social feedback may require unnecessary computing by individual agents and/or may nullify the possible benefits of noise. In this study, we investigate the delicate balance between social feedback and noise, and its relationship with collective coherence. We perform our analysis through a locust-inspired case study of coherently marching agents, modelling the binary collective decision-making problem of symmetry breaking. For this case study, we analytically approximate the minimal number of communication links necessary to attain maximum collective coherence. To validate our findings, we simulate a 500-robot swarm and obtain good agreement between theoretical results and physics-based simulations. We illustrate through simulation experiments how the robot swarm, using a decentralised algorithm, can adaptively reach coherence for various noise levels by regulating the number of communication links. Moreover, we show that when the system is disrupted by increasing and decreasing the robot density, the robot swarm adaptively responds to these changes in real time. This decentralised adaptive behaviour indicates that the derived relationship between social feedback, noise and coherence is robust and swarm size independent.