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The nonreciprocal property of quantum systems is crucial for chiral quantum networks. In this study, a phase‐controlled scheme is proposed to enhance the nonreciprocal quantum entanglement and optical transmission in a cavity optomechanical system by introducing a phase‐dependent unidirectional coupling between two whispering‐gallery‐mode (WGM) resonators. The Sagnac effect induced by the spinning resonator generates nonreciprocity, while the interference effect between direct evanescent coupling and indirect phase‐dependent unidirectional coupling significantly enhances entanglement under the anti‐Stokes sideband. For specific coupling phases, ideal nonreciprocity can be achieved in both entanglement and transmission. The proposed phase‐controlled nonreciprocity presented offers an effective strategy for constructing a unidirectional quantum channel and implementing an optical diode in chiral quantum networks, thereby opening up new possibilities for applications in quantum technologies. [ABSTRACT FROM AUTHOR]

The purpose of this work is to research the numerical results of the comparison of the synchronization speed of ring neural networks with unidirectional and bidirectional coupling. Each neuron is linearly coupled with the others and represented by a system of reaction-diffusion equations of the FitzHugh-Nagumo type. The result shows that the necessary coupling strength for the synchronization in two cases increases when the number of neurons increases. In other words, the greater the number of neurons in the ring networks is, the more difficult the synchronization occurs. Moreover, synchronizing the ring networks with bidirectional coupling is easier than the one with unidirectional coupling over the same given number of neurons. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamics of a chain of unidirectionally coupled non-identical Van der Pol (VdP) oscillators driven by a sinusoidal signal at the first node. Starting with a random generation of frequencies in the chain of standard VdP systems, we numerically study the influence of a small and a large value of disorder. It can be seen that disorder reduces the signal amplitude propagating along the chain and induces a coexistence of different dynamical states, namely periodic, quasiperiodic and chaotic states in the chain, which tend to disappear by suitably adjusting the coupling strength. A mathematical justification of the obtained dynamics is provided using multiple time-scale methods. Taking into account the cubic nonlinearity, the chain remains more or less coherent, no generation of the plateau of amplitude is observed for large disorder and the signal amplitude fluctuates greatly along the chain. Considering a chirp distribution of frequencies, the signal amplitude is characterised by a parabolic decrease followed by an irregular series of jumps back to a certain value. These effects are largely reduced by a moderate coupling strength and the presence of cubic nonlinearity. [ABSTRACT FROM AUTHOR]

The directional coupling of single photon emission from nitrogen vacancy (NV–) emitters to optical systems for various applications requires a suitable interface between NV– emitters and optical waveguides. Unidirectional coupling of photons may have significant importance in next generation quantum technology such as quantum and complex optical networks, quantum communication, and multi‐scale quantum photonics devices including quantum non‐linearity and quantum metrology. Here, a hybrid asymmetric structure of elliptically faceted (ELFA) diamond nanowire with Bragg grating (BG) containing negatively charged NV– center for efficient and unidirectional optical coupling to optical nanowire (waveguide) is proposed. The calculations indicate that the structure can provide coupling efficiency of ≈90% toward the elliptically facet direction and ≈1% in the opposite direction. Further, Purcell factor is enhanced due to the augmented electric field intensity in the ELFA structure. This structure is significantly robust against imperfect placement and rotational alignment of dipole from its intended position. [ABSTRACT FROM AUTHOR]

• The presence of unpredictable oscillations in SICNNs with delay is rigorously proved. • Rectangular input currents are used to generate unpredictable oscillations. • Unpredictable oscillations in coupled retarded SICNNs are demonstrated. • The control of the unpredictable behavior is performed. We rigorously prove that unpredictable oscillations take place in the dynamics of shunting inhibitory cellular neural networks (SICNNs) with delay when rectangular input currents generated by an unpredictable sequence are utilized. The existence, uniqueness, and exponential stability of such oscillations are discussed. The contraction mapping principle is applied to achieve the theoretical results. Numerical simulations supporting the presence of unpredictable oscillations are provided, and the transfer of unpredictable behavior between SICNNs under unidirectional coupling is demonstrated. It is also shown by means of the delayed feedback control method that the obtained unpredictable behavior is controllable. Moreover, an application to secure communication is discussed. [ABSTRACT FROM AUTHOR]

We propose and demonstrate experimentally a scheme for simultaneously generating multi-channel broadband chaotic signals based on two unidirectionally coupled weak-resonant-cavity Fabry-Perot laser diodes (WRC-FPLDs) with almost the same mode interval, where one WRC-FPLD is utilized as master WRC-FPLD (M-WRC-FPLD) and the other is used as slave WRC-FPLD (S-WRC-FPLD). Under the optical injection from the M-WRC-FPLD with suitable injection parameters, multiple longitudinal modes of the S-WRC-FPLD can be simultaneously driven into chaotic states, which can provide multi-channel chaotic signals. Via a tunable optical filter, we inspect the performances of 9-channel chaotic signals, the results show that the chaotic bandwidths are within the range of 8~15 GHz for all the 9-channel chaotic signals. Furthermore, the influences of the injection power and frequency detuning on the performances of the chaotic output from one of the channels are also analyzed.

In this study, we investigate the dynamics of impulsive systems driven by a chaotic system. It is shown that the response impulsive system replicates the sensitivity and the period-doubling cascade of the drive. Illustrative examples that support the theoretical results are provided.

Valley photonic crystal is a typical strategy of topological photonics with promising applications for novel integrated waveguides. The valley pseudospin provides an intrinsic paradigm to implement unidirectional coupling with robustly optical transport. But the key issue on the analysis of unidirectional coupling based on topological modes is lack of deep understanding on valley photonic crystals. In this work, we systematically study the mechanism and performance of unidirectional coupling between valley photonic crystal waveguides and chiral dipole emitters. Forming by two topologically-distinct valley photonic crystals, there are two types of valley-interface waveguides, i.e. bearded stack with glide-plane symmetry and zigzag stack with inversion symmetry. Analytical derivation shows that the Stokes parameters of topological eigenmodes can predict the directionality in the above two types of valley-interface waveguides, which is also confirmed by full-wave simulations. The strategy of bearded valley-interface waveguide can be easier to achieve high efficiency of unidirectional coupling than the zigzag case, and can relax the bias error of frequency and source location. It is also proved that the topological-protected unidirectional coupling supports robust transport against sharp-bending interface. Finally, we give a brief summary and perspective in the development of topological integrated photonics. This work gives a deterministic guidance on chiral light-matter interaction based on topological photonics, as well as shows the outlook of topological integrated photonics. [ABSTRACT FROM AUTHOR]

We theoretically investigate the sensitivity of the beat frequency in a coupled oscillatory system comprising two originally synchronized similar or dissimilar oscillators up on weak perturbation of the frequency of one of the oscillators. Based on the well-known Kuramoto model, we analytically show that the variation of the beat frequency near the synchronization edge of two coupled oscillators induced by external perturbation of one of the oscillators, is much larger than the frequency shift of an isolated oscillator induced by the same level of perturbation. The theoretical predications are validated by experimental measurements of the response of two different coupled oscillatory systems to external perturbation: 1) Two bidirectionally coupled electronic Colpitts oscillators, when a photo induced current is applied to one of them. 2) An electronic oscillator unidirectionally coupled to an optoelectronic oscillator (OEO), when the temperature of the delay line of the OEO is changed. [ABSTRACT FROM AUTHOR]

We propose and demonstrate experimentally a scheme for simultaneously generating multi-channel broadband chaotic signals based on two unidirectionally coupled weak-resonant-cavity Fabry-Perot laser diodes (WRC-FPLDs) with almost the same mode interval, where one WRC-FPLD is utilized as master WRC-FPLD (M-WRC-FPLD) and the other is used as slave WRC-FPLD (S-WRC-FPLD). Under the optical injection from the M-WRC-FPLD with suitable injection parameters, multiple longitudinal modes of the S-WRC-FPLD can be simultaneously driven into chaotic states, which can provide multi-channel chaotic signals. Via a tunable optical filter, we inspect the performances of 9-channel chaotic signals, the results show that the chaotic bandwidths are within the range of 8∼15 GHz for all the 9-channel chaotic signals. Furthermore, the influences of the injection power and frequency detuning on the performances of the chaotic output from one of the channels are also analyzed. [ABSTRACT FROM AUTHOR]

We investigate experimentally and theoretically the communication of inhibited spiking dynamics between two interlinked photonic neurons based upon the vertical-cavity surface-emitting lasers (VCSELs). We show that the sub-nanosecond speed spiking dynamics fired by a Transmitter-VCSEL (T-VCSEL) can be inhibited under the arrival of suitable external stimuli and that the inhibited spiking behaviors are propagated into another Receiver-VCSEL (R-VCSEL). Both VCSELs exhibit analogous inhibited spiking dynamics in response to stimuli with different temporal durations and strength. In addition, a very good agreement is found between theoretical simulations and experiments. These results offer greater prospects for future networks of VCSEL-based photonic neurons for neuromorphic computing platforms.

In this study, we present a new method for assessing the functional connectivity between the drive and the noisy response chaotic oscillators with significant frequency mismatch. This method is based on the footprint of the drive oscillator on the response oscillator. Specifically, we calculate the magnitude squared coherence between the intrinsic frequency of the drive oscillator and the oscillation frequency of the dynamics of the spectral energy of the response oscillator. The spectral energy of the response oscillator is estimated using a modified S-transform algorithm with a short sliding window. We apply the proposed approach to master–slave Rössler systems and coupled Van der Pol oscillators with a frequency ratio of ∼ 1:4 and show that when the slave signal is contaminated with white Gaussian noise at different signal-to-noise ratios (SNR), the new algorithm is well suited to assess the presence of coupling with a priori known direction in noisy, unidirectionally coupled chaotic oscillators, especially in the case of weak and moderate coupling. [ABSTRACT FROM AUTHOR]

In this paper, the problem of finite-time synchronisation of uncertain delay spatiotemporal networks via unidirectional coupling technology is investigated. Based on Lyapunov theorem and finite-time stability theory, an effective finite-time synchronisation scheme is designed to achieve finite-time synchronisation between uncertain delay spatiotemporal networks, and adaptive estimations of coupling coefficient, unknown parameter and uncertain network topology are realised. Then, the Fisher–Kolmogorov spatiotemporal model is used as the state equation of the network node for numerical simulation. The simulation results show that the finite-time synchronisation scheme is effective. [ABSTRACT FROM AUTHOR]

In the present work, we present a new algorithm for assessing causality in uni-directionally coupled chaotic oscillators with small frequency mismatch embedded in heavy white Gaussian noise. This method is based on the correlation between changes in the phase dynamics of the slave oscillator and the dynamics of the phase difference between the oscillators. To recover the phase at low signal-to-noise ratio, a nonlinear adaptive denoising algorithm based on finding sinusoidal fits to the local neighbourhood of the reconstructed phase space is used. Application of the proposed approach to master-slave Rössler systems showed that the new algorithm is well-suited for assessing the presence and direction of coupling in highly noisy uni-directionally coupled chaotic oscillators, especially in the case of weak and moderate coupling. [ABSTRACT FROM AUTHOR]

We study numerically external synchronization of chimera states in a network of many unidirectionally coupled layers, each representing a ring of nonlocally coupled discretetime systems. The dynamics of each element in the network is described by either the logistic map or the bistable cubic map. We consider two cases: when all M unidirectionally coupled layers are identical and when (M − 1) identical layers differ from the first driving layer in their nonlocal coupling parameters. It is shown that the master chimera state in the first layer can be retranslating along the network with small distortions which are defined by a parameter mismatch. We also analyze the dependence of the mean-square deviation of the structure in the ith layer on the nonlocal coupling parameters. [ABSTRACT FROM AUTHOR]

In this paper, we present some improvements to the convergent cross mapping (CCM) algorithm for detecting causality in uni-directionally connected chaotic systems. The basic concept of the CCM algorithm is that the causal influence of system X on system Y appears as mapping of the neighbouring states in the reconstructed d-dimensional manifold, My, to the neighbouring states in the reconstructed d-dimensional manifold, Mx, and this effect is evaluated using the correlation coefficient between the estimated and observed values of Mx. We proposed a composite indicator of causality as the ratio between the correlation coefficient and the Shannon entropy of the distribution of the residuals between the estimated and observed values of Mx. Application of the proposed approach to four master-slave Rössler and Lorenz systems and real-world data showed that the new algorithm allowed a slight increase in capability to reveal the presence and direction of couplings. [ABSTRACT FROM AUTHOR]

Time delay is inevitable in unidirectionally coupled drive-free vibratory gyroscope system. The effect of time delay on the gyroscope system is studied in this paper. To this end, amplitude death and Hopf bifurcation induced by small time delay are first investigated by analyzing the related characteristic equation. Then, the direction of Hopf bifurcations and stability of Hopf-bifurcating periodic oscillations are determined by calculating the normal form on the center manifold. Next, spatiotemporal patterns of these Hopf-bifurcating periodic oscillations are analyzed by using the symmetric bifurcation theory of delay differential equations. Finally, it is found that numerical simulations agree with the associated analytic results. These phenomena could be induced although time delay is very small. Therefore, it is shown that time delay is an important factor which influences the sensitivity and accuracy of the gyroscope system and cannot be neglected during the design and manufacture. [ABSTRACT FROM AUTHOR]

In this work, the case of coupling between chaotic nonlinear circuits via a memristor, is studied. As a circuit, the most well-known nonlinear circuit, the circuit of Chua oscillator, is chosen. The two identical circuits are coupled unidirectionally via the HP’s memristor, by using a recently new proposed window function. The simulation results show a variety of dynamical phenomena, such as chaotic synchronization and on-off intermittency, depending on memristor’s initial state and the parameters of the chosen window function.

Chaotic systems are characterized by sensitive dependence on initial conditions, similar to random behavior, and continuous broad-band power spectrum. Chaos is a good potential to be used in secure communications system. In this paper, in order to show some interesting phenomena of three-order Jerk circuit with modulus nonlinearity, the chaotic behavior as a function of a variable control parameter, has been studied. The initial study in this paper is to analyze the phase portraits, the Poincaré maps, the bifurcation diagrams, while the analysis of the synchronization in the case of unidirectional coupling between two identical generated chaotic systems, has been presented. Moreover, some appropriate comparisons are made to contrast some of the existing results. Finally, the effectiveness of the unidirectional coupling scheme between two identical Jerk circuits in a secure communication system is presented in details. Integration of theoretical physics, the numerical simulation by using MATLAB 2010, as well as the implementation of circuit simulations by using MultiSIM 10.0 has been performed in this study

The last decades, the synchronization between coupled chaotic circuits has attracted the interest of the research community because it is a rich and multi-disciplinary phenomenon with broad range applications, such as in broadband communication systems, in secure communications and in cryptography. For this reason many coupling schemes between identical nonlinear circuits with chaotic behavior have been presented. However, the basic drawback of the majority of these schemes is the request the coupled circuits to be identical, due to the fact that in real world applications this is impossible. Motivated by the aforementioned inevitable feature of this class of circuits, which drives the systems out of synchronization, a unidirectional coupling scheme between non-identical, nonlinear circuits, is presented in this work. The circuit, which is used, realizes a four-dimensional modified Lorenz system, which is capable of producing chaotic and hyperchaotic attractors. Furthermore, the coupling scheme is designed by using Nonlinear Open Loop Controllers to target the synchronization state. The stability of synchronization is ensured by using Lyapunov function stability theory. Simulation results of the proposed coupling scheme by using SPICE are also presented to verify the feasibility of the proposed coupling scheme. [ABSTRACT FROM AUTHOR]

In this letter, a theoretical model is proposed to calculate the coupling efficiency of surface plasmon polaritons (SPPs) by a single slit on the metal film. In contrast to previous work developed for normal incident light only, TM0 and TM1 modes of the slit are incorporated in the model, which makes it applicable for the case of oblique incidence. Numerical simulations confirm that this two-mode model can accurately predict the coupling efficiency of SPPs by slits with subwavelength widths ( $< \lambda $ ). Moreover, we demonstrate that unidirectional SPPs can be coupled by an oblique incident light beam, which can be explained by the generation and interference of these two modes in the slit. [ABSTRACT FROM PUBLISHER]

We study the bifurcation structures in three unidirectionally coupled nonlinear electromechanical systems (EMS) with no external signal. The coupling between the systems is realized with integrator operational amplifiers. It is found that the magnetic field and the damping coefficient control the appearance of Hopf bifurcation. By varying the coupling coefficient, various dynamical behaviors corresponding to different types of bifurcation are observed. A special case having one linear EMS unidirectionally coupled to two nonlinear EMS also shows a series of bifurcation leading to periodicity, quasiperiodicity, chaos, hyperchaos and then again periodic states. Finally taking into consideration a time delay due to regenerative process, it is found that for small time delay and regenerative process strength, the system remains motionless, leading to periodic oscillation at critical value, then quasiperiodicity, chaos and instability as the delay and the regenerative process strength increase. [ABSTRACT FROM AUTHOR]

Based on the unidirectional propagation property of a single coupler composed of two parallel rectangular slots with different lengths, a near infrared broadband circular surface plasmonic lens is proposed. Multiple identical couplers are arranged on the two concentric circles each of which has half of the total couplers. The numerical investigation using the finite difference in time domain method is performed. The results show that when a radially polarized beam is directed onto the surface plasmonic lens from the side of the substrate, a highly enhanced and confined, dominantly longitudinal polarized nanoscale electromagnetic field spot can be obtained in the center of this circular lens. Various simulations are conducted to optimize the nanostructure. It is demonstrated that, with the optimized lens nanostructure, the extinction ratio of the intensity of the hot spot to the maximum intensity of the off-lens areas is more than 24 within the bandwidth of more than 224 nm. This characterization attributes to the unidirectional propagation property of a single coupler. The high extinction ratio can minimize the outward propagating surface plasmonic energy which may cause the noise and unnecessary coupling with the adjacent nanostructure in the circuit. [ABSTRACT FROM AUTHOR]

A polarization-sensitive V-shaped slot nanoantenna column is utilized to realize tunable unidirectional coupling of surface plasmon polaritons (SPP). Two plasmon resonant modes are excited in the V-shaped slot nanoantennas with x- and y-polarized incident light, respectively. The electric fields of coupled SPP show different symmetries corresponding to that of the two resonant modes. Linear combinations of the two resonant modes result in asymmetric SPP intensity distributions. As a result, by controlling the incident polarizations, tunable unidirectional coupling of SPP to two opposite directions perpendicular to the column at different wavelengths are realized. A highest extinction ratio of 36.7 dB is achieved, and the extinction ratio keeps larger than 7 dB within a wavelength of 149 nm. [ABSTRACT FROM AUTHOR]

In this work, the case of coupling between chaotic nonlinear circuits via a memristor, is studied. As a circuit, the most well-known nonlinear circuit, the circuit of Chua oscillator, is chosen. The two identical circuits are coupled unidirectionally via the HP's memristor, by using a recently new proposed window function. The simulation results show a variety of dynamical phenomena, such as chaotic synchronization and on-off intermittency, depending on memristor's initial state and the parameters of the chosen window function. [ABSTRACT FROM AUTHOR]

Recently, highly resolved experiments and simulations have provided detailed insight into the dynamics of turbulent pipe flow. This has revived the interest in identifying mechanisms that generate chaotic transients with superexponential growth of lifetime as a function of a control parameter, the Reynolds number for pipe flow, and with transitions from bounded chaotic patches to an invasion of space of irregular motion. Dynamical systems models are unique tools in this respect because they can provide insight into the origin of the very long lifetime of puffs, and the dynamical mechanism leading to the transition from puffs to slugs in pipe flow. The present paper contributes to this enterprise by introducing a unidirectionally coupled map lattice. It mimics three of the salient features of pipe-flow turbulence: (i) the transition from laminar flow to puffs, (ii) a superexponential scaling of puff lifetime, and (iii) the transition from puffs to slugs by an unbinding transition in an intermittency scenario. In our model all transitions and scalings are theoretically described from a dynamical systems point of view. [ABSTRACT FROM AUTHOR]

It is shown that the approach based on the Granger causality may lead to erroneous conclusions about bidirectional coupling (BC) in the case of unidirectional coupling (UC) and quite a sparse sample of the data series analyzed. This effect was revealed in an analysis of coupling between variations in the solar irradiance and global surface temperature. We present a statistical test to confirm or reject speculations about the character (unidirectional or bidirectional) of coupling. The corresponding analysis of coupling between phenomena of El Niño and the Indian Monsoon confirmed the earlier conclusions about their mutual influence. [ABSTRACT FROM AUTHOR]

Chaotic systems are characterized by sensitive dependence on initial conditions, similar to random behavior, and continuous broad-band power spectrum. Chaos is a good potential to be used in secure communications system. In this paper, in order to show some interesting phenomena of three-order Jerk circuit with modulus nonlinearity, the chaotic behavior as a function of a variable control parameter, has been studied. The initial study in this paper is to analyze the phase portraits, the Poincaré maps, the bifurcation diagrams, while the analysis of the synchronization in the case of unidirectional coupling between two identical generated chaotic systems, has been presented. Moreover, some appropriate comparisons are made to contrast some of the existing results. Finally, the effectiveness of the unidirectional coupling scheme between two identical Jerk circuits in a secure communication system is presented in details. Integration of theoretical physics, the numerical simulation by using MATLAB 2010, as well as the implementation of circuit simulations by using MultiSIM 10.0 has been performed in this study. [ABSTRACT FROM AUTHOR]

Abstract: The Hindmarsh–Rose (HR) dynamical system is a well-known model of neuronal activity. It is known that two HR neurons can synchronize when coupled in the action potential variable. Here, I report on exponentially fast synchronization of two HR neurons with novel unidirectional coupling. Explicit proof of global stability is given where the Lyapunov function is found with single parameter bounds as sufficient criteria. Numerical explorations verify such synchronization yet reveal additional single-link unidirectional couplings enabling full or subsystem synchronization where the parameters of two HR neurons might differ. Despite the mathematical prediction, from neuroscience and molecular biology points of view such connectivity between neurons has no simple explanation. The result opens up a fundamental question on the valid interpretation of unidirectional links, their potential use, and if such synchronization is an active principle of biological neurons. [Copyright &y& Elsevier]

This paper proposes methods for designing bidirectionally coupled systems via generalized synchronization technique. Starting from a chaotic system we are constructing synchronized bidirectionally coupled driving and response systems. Numerical simulation results are presented to prove the effectiveness of the scheme. [ABSTRACT FROM AUTHOR]

Abstract: Rotating waves in a ring of unidirectionally coupled Lorenz systems are studied. When a single system is bistable and nonchaotic, various rotating waves are generated and bifurcated in the ring of systems. We consider two kinds of rotating waves: exponential transient rotating waves and chaotic rotating waves. Exponential transient rotating waves are those the duration of which increases exponentially with the number of systems in the ring. Chaotic rotating waves are caused through interactions between periodic rotating waves of multiple wave numbers. [Copyright &y& Elsevier]