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Given the structure of a large-scale complex network and the nodal dynamics are known, can we predict all the possible synchronization patterns to be emerged and, in addition, the conditions for generating these patterns? Whereas this question has been broadly interested and extensively studied, the existing methods require a priori knowledge of the network symmetries and, additionally, a perfect network symmetry. Recently, Huawei Fan, et al., proposed a general framework for [Detail] ...
Download coverWhereas topological symmetries have been recognized as crucially important to the exploration of synchronization patterns in complex networks of coupled dynamical oscillators, the identification of the symmetries in large-size complex networks remains as a challenge. Additionally, even though the topological symmetries of a complex network are known, it is still not clear how the system dynamics is transited among different synchronization patterns with respect to the coupling strength of the oscillators. We propose here the framework of eigenvector-based analysis to identify the synchronization patterns in the general complex networks and, incorporating the conventional method of eigenvalue-based analysis, investigate the emergence and transition of the cluster synchronization states. We are able to argue and demonstrate that, without a prior knowledge of the network symmetries, the method is able to predict not only all the cluster synchronization states observable in the network, but also the critical couplings where the states become stable and the sequence of these states in the process of synchronization transition. The efficacy and generality of the proposed method are verified by different network models of coupled chaotic oscillators, including artificial networks of perfect symmetries and empirical networks of non-perfect symmetries. The new framework paves a way to the investigation of synchronization patterns in large-size, general complex networks.
Analytical expressions for scaling of brain wave spectra derived from the general nonlinear wave Hamiltonian form show excellent agreement with experimental “neuronal avalanche” data. The theory of the weakly evanescent nonlinear brain wave dynamics [Phys. Rev. Research 2, 023061 (2020); J. Cognitive Neurosci. 32, 2178 (2020)] reveals the underlying collective processes hidden behind the phenomenological statistical description of the neuronal avalanches and connects together the whole range of brain activity states, from oscillatory wave-like modes, to neuronal avalanches, to incoherent spiking, showing that the neuronal avalanches are just the manifestation of the different nonlinear side of wave processes abundant in cortical tissue. In a more broad way these results show that a system of wave modes interacting through all possible combinations of the third order nonlinear terms described by a general wave Hamiltonian necessarily produces anharmonic wave modes with temporal and spatial scaling properties that follow scale free power laws. To the best of our knowledge this has never been reported in the physical literature and may be applicable to many physical systems that involve wave processes and not just to neuronal avalanches.
Heavy flavour physics provides excellent opportunities to indirectly search for new physics at very high energy scales and to study hadron properties for deep understanding of the strong interaction. The LHCb experiment has been playing a leading role in the study of heavy flavour physics since the start of the LHC operations about ten years ago, and made a range of high-precision measurements and unexpected discoveries, which may have far-reaching implications on the field of particle physics. This review highlights a selection of the most influential physics results on CP violation, rare decays, and heavy flavour production and spectroscopy obtained by LHCb using the data collected during the first two operation periods of the LHC. The upgrade plan of LHCb and the physics prospects are also briefly discussed.
Accessing a full image of the inner content of hadrons represents a central endeavour of modern particle physics, with the main scientific motivation to investigate the strong interaction binding the visible matter. On the one hand, the structure of known exotic candidates is a fundamental open issue addressed widely by scientists. On the other hand, looking for new states of exotic nature is a central component for theoretical and experimental efforts from electron-positron machine and electron accelerator with fixed target to heavy ion and electron-ion colliders. In this article we present a succinct short overview of the attempt to search for exotic narrow N∗ and Z states containing light quarks only or also charm, and its connotation for bottom regions (the latter two are also known as Pc (Zc) and Pb (Zb) states, respectively in the literature). We address the effort of searching for exotic narrow N∗ and Z states in light quark sector. We focus on recent progress in searching for signal of Pc and Zc states photoproduction and its implication into the Pb and Zb photoproduction and their decay properties. We also discuss future perspectives for the field in electron-ion colliders, a good place to disentangle the nature of some of these states and investigate some other enlightening topics including QCD trace anomaly and quarkonium-nucleon scattering length.
Precise measurements of the boron-to-carbon and boron-to-oxygen ratios by DAMPE show clear hardenings around 100 GeV/n, which provide important implications on the production, propagation, and interaction of Galactic cosmic rays. In this work we investigate a number of models proposed in literature in light of the DAMPE findings. These models can roughly be classified into two classes, driven by propagation effects or by source ones. Among these models discussed, we find that the re-acceleration of cosmic rays, during their propagation, by random magnetohydrodynamic waves may not reproduce sufficient hardenings of B/C and B/O, and an additional spectral break of the diffusion coefficient is required. The other models can properly explain the hardenings of the ratios. However, depending on simplifications assumed, the models differ in their quality in reproducing the data in a wide energy range. The models with significant re-acceleration effect will under-predict low-energy antiprotons but over-predict low-energy positrons, and the models with secondary production at sources over-predict high-energy antiprotons. For all models high-energy positron excess exists.
Two-dimensional (2D) black phosphorus (BP) has attracted great attention in recent years in fundamental research as well as optoelectronics applications. The controllable synthesis of high-quality BP is vital to the investigation of its intrinsic physical properties and versatile applications. Originally, BP was mostly synthesized under high temperatures and pressures. Subsequently, metal flux, wet chemical and chemical vapor transport (CVT) methods had been appeared successively. The pulsed laser deposition (PLD) and CVT methods have been used to prepare high-quality BP thin films on silicon substrates, which is significant for its monolithic integration and practical applications. To meet the demand of the scalable applications of BP, the direct preparation of BP films on dielectric substrates that avoids additional transfer process, is crucial to high-performance device implementation. In this review, the growing methods and corresponding mechanisms of BP are summarized and analyzed. Meanwhile, the view on the controllable growth of large-area, high-quality BP films is envisioned.
We review the description and modeling of transport phenomena among the electron systems coupled via scalar or vector photons. It consists of three parts. The first part is about scalar photons, i.e., Coulomb interactions. The second part is with transverse photons described by vector potentials. The third part is on ϕ = 0 or temporal gauge, which is a full theory of the electrodynamics. We use the nonequilibrium Green’s function (NEGF) formalism as a basic tool to study steady-state transport. Although with local equilibrium it is equivalent to the fluctuational electrodynamics (FE), the advantage of NEGF is that it can go beyond FE due to its generality. We have given a few examples in the review, such as transfer of heat between graphene sheets driven by potential bias, emission of light by a double quantum dot, and emission of energy, momentum, and angular momentum from a graphene nanoribbon. All of these calculations are based on a generalization of the Meir−Wingreen formula commonly used in electronic transport in mesoscopic systems, with materials properties represented by photon self-energy, coupled with the Keldysh equation and the solution to the Dyson equation.
Ionic liquids (ILs) are expected to be used as readily available “designer” solvents, characterized by a number of tunable properties that can be obtained by modulating anion and cation combinations and ion chain lengths. Among them, its high ionicity is outstanding in the preparation and property modulation of two-dimensional (2D) materials. In this review, we mainly focus on the ILs-assisted exfoliation of 2D materials towards large-scale as well as functionalization. Meanwhile, electric-field controlled ILs-gating of 2D material systems have shown novel electronic, magnetic, optical and superconducting properties, attracting a broad range of scientific research activities. Moreover, ILs have also been extensively applied in various field practically. We summarize the recent developments of ILs modified 2D material systems from the electrochemical, solar cells and photocatalysis aspects, discuss their advantages and possibilities as “designer solvent”. It is believed that the design of ILs accompanying with diverse 2D materials will not only solve several scientific problems but also enrich materials design and engineer of 2D materials.
Moiré superlattices created by stacking different pieces of two-dimensional layered materials with a slight lattice mismatch have recently emerged as an exceptional platform for exploring emergent quantum phenomena. In stark contrast to the “parent” materials, the electronic band structures are significantly modified from moiré engineering due to the large-scale periodic moiré potential and interlayer hybridization. In this paper, we mainly focus on the recent progresses achieved in graphene-based moiré systems which have been a condensed-matter playground showing unprecedented abundance of quantum states such as strongly correlated states, superconductivity and novel band topologies.
As a two-dimensional material with a hollow hexatomic ring structure, Néel-type anti-ferromagnetic (AFM) GdI3 can be used as a theoretical model to study the effect of electron doping. Based on first-principles calculations, we find that the Fermi surface nesting occurs when more than 1/3 electron per Gd is doped, resulting in the failure to obtain a stable ferromagnetic (FM) state. More interestingly, GdI3 with appropriate Mg/Ca doping (1/6 Mg/Ca per Gd) turns to be half-metallic FM state. This AFM−FM transition results from the transfer of doped electrons to the spatially expanded Gd-5d orbital, which leads to the FM coupling of local half-full Gd-4f electrons through 5d−4f hybridization. Moreover, the shortened Gd−Gd length is the key to the formation of the stable ferromagnetic coupling. Our method provides new insights into obtaining stable FM materials from AFM materials.
Two-dimensional layered materials (2DLMs) have attracted growing attention in optoelectronic devices due to their intriguing anisotropic physical properties. Different members of 2DLMs exhibit unique anisotropic electrical, optical, and thermal properties, fundamentally related to their crystal structure. Among them, directional heat transfer plays a vital role in the thermal management of electronic devices. Here, we use density functional theory calculations to investigate the thermal transport properties of representative layered materials: β-InSe, γ-InSe, MoS2, and h-BN. We found that the lattice thermal conductivities of β-InSe, γ-InSe, MoS2, and h-BN display diverse anisotropic behaviors with anisotropy ratios of 10.4, 9.4, 64.9, and 107.7, respectively. The analysis of the phonon modes further indicates that the phonon group velocity is responsible for the anisotropy of thermal transport. Furthermore, the low lattice thermal conductivity of the layered InSe mainly comes from low phonon group velocity and atomic masses. Our findings provide a fundamental physical understanding of the anisotropic thermal transport in layered materials. We hope this study could inspire the advancement of 2DLMs thermal management applications in next-generation integrated electronic and optoelectronic devices.
Silicon carbide nanosheets (SiCNSs) have a very broad application prospect in the field of new two-dimensional (2D) materials. In this paper, the interlayer interaction mechanism of bilayer SiCNSs (BL-SiCNSs) and its effect on optical properties are studied by first principles. Taking the charge and dipole moment of the layers as parameters, an interlayer coupling model is constructed which is more convenient to control the photoelectric properties. The results show that the stronger the interlayer coupling, the smaller the band gap of BL-SiCNSs. The interlayer coupling also changes the number of absorption peaks and causes the red or blue shift of absorption peaks. The strong interlayer coupling can produce obvious dispersion and regulate the optical transmission properties. The larger the interlayer distance, the smaller the permittivity in the vertical direction. However, the permittivity of the parallel direction is negative in the range of 150-300 nm, showing obvious metallicity. It is expected that the results will provide a meaningful theoretical basis for further study of SiCNSs optoelectronic devices.
Dual topological insulator (DTI), which simultaneously hosts topological insulator (TI) and topological crystalline insulator (TCI) phases, has attracted extensive attention since it has a better robustness of topological nature and broad application prospects in spintronics. However, the realization of DTI phase in two-dimensional (2D) system is extremely scarce. By first-principles calculations, we predict that the 2D rectangular bismuth (R−Bi) bilayer is a novel DTI, featured by
As a revolutionary observation tool in life science, biomedical, and material science, optical microscopy allows imaging of samples with high spatial resolution and a wide field of view. However, conventional microscopy methods are limited to single imaging and cannot accomplish real-time image processing. The edge detection, image enhancement and phase visualization schemes have attracted great interest with the rapid development of optical analog computing. The two main physical mechanisms that enable optical analog computing originate from two geometric phases: the spin-redirection Rytov-Vlasimirskii-Berry (RVB) phase and the Pancharatnam-Berry (PB) phase. Here, we review the basic principles and recent research progress of the RVB phase and PB phase based optical differentiators. Then we focus on the innovative and emerging applications of optical analog computing in microscopic imaging. Optical analog computing is accelerating the transformation of information processing from classical imaging to quantum techniques. Its intersection with optical microscopy opens opportunities for the development of versatile and compact optical microscopy systems.
We propose a method to generate the multi-mode entangled catalysis squeezed vacuum states (MECSVS) by embedding the cross-Kerr nonlinear medium into the Mach−Zehnder interferometer. This method realizes the exchange of quantum states between different modes based on Fredkin gate. In addition, we study the MECSVS as the probe state of multi-arm optical interferometer to realize multi-phase simultaneous estimation. The results show that the quantum Cramer−Rao bound (QCRB) of phase estimation can be improved by increasing the number of catalytic photons or decreasing the transmissivity of the optical beam splitter using for photon catalysis. In addition, we also show that even if there is photon loss, the QCRB of our photon catalysis scheme is lower than that of the ideal entangled squeezed vacuum states (ESVS), which shows that by performing the photon catalytic operation is more robust against photon loss than that without the catalytic operation. The results here can find applications in quantum metrology for multiparatmeter estimation.
Quantum communication network scales point-to-point quantum communication protocols to more than two detached parties, which would permit a wide variety of quantum communication applications. Here, we demonstrate a fully-connected quantum communication network, exploiting three pairs of Einstein−Podolsky−Rosen (EPR) entangled sideband modes, with high degree entanglement of 8.0 dB, 7.6 dB, and 7.2 dB. Each sideband modes from a squeezed field are spatially separated by demultiplexing operation, then recombining into new group according to network requirement. Each group of sideband modes are distributed to one of the parties via a single physical path, making sure each pair of parties build their own private communication links with high channel capacity better than any classical scheme.
Diode-pumped alkali lasers, possessing high efficiency and narrow linewidth, can provide feasible solutions for wavelength ranges difficult to reach by commercial lasers. In this study, we investigate a generation of coherent blue light (CBL) via four-wave mixing (FWM)-based up-conversion processes in cesium (Cs) vapor. A bichromatic pumping scheme with 852- and 917-nm lasers drives the Cs atoms to the 6D5/2 excited level, followed by cascaded decay of 6D5/2 → 7P3/2 → 6S1/2, producing 456-nm CBL under phase matching conditions. The fluorescence in multiple bands from blue to near- and far-infrared in the FWM process is demonstrated under different experimental conditions. To optimize the experimental parameters, we investigate the dependence of 456-nm CBL on the vapor temperature, frequency, and intensity of the two pump lasers. A maximum power of 2.94 mW is achieved with pump powers of 430 mW (for 852 nm) and 470 mW (for 917 nm). The corresponding conversion efficiency is 1.5%/W, three-fold higher than those in previous studies. Our results can contribute to fundamental research on atom−photon interactions and quantum metrology.
Pancharatnam−Berry (PB) phase metasurface, as a special class of gradient metasurfaces, has been paid much attention owing to the robust performance for phase control of circularly polarized waves. Herein, we present an element-based polarizer for the first step, which enables the incident electromagnetic waves into the cross-polarized waves with the relative bandwidth of 71%, and the polarization conversion ratio exceeds 90% at 6.9−14.5 GHz. Then an eight-elements coding polarizer based on the PB phase is presented for the applications on beam control and radar cross section reduction. The simulated values indicate that the reduction of radar cross section is more than 10 dB at 6−16 GHz. Our work reveals the availability of manipulating the waves, beamforming in communication systems and electromagnetic stealth, and so on.
Yb3+:YAG crystal is one excellent material for developing high-power radiation-balanced lasers (RBLs). An experimental study of the laser cooling performances of YAG crystals with various doping Yb3+ concentrations, especially for application of RBLs, is reported here. With improved Yb3+ doping concentration in YAG crystal, though the resonance absorption coefficient increases, the corresponding external quantum efficiency has been found to decrease with the average fluorescence wavelength being red shifted, which is detrimental to anti-Stokes fluorescence (ASF) cooling. The decrease of the external quantum efficiency can cause the first zero crossing wavelength to red shift, which is not conducive to RBLs. Based on the comprehensive study of the cooling characteristics of the series of Yb3+-doped YAG crystals, the optimal Yb3+ doping concentration for ASF cooling has been suggested.
We present protocols to generate quantum entanglement on nonlocal magnons in hybrid systems composed of yttrium iron garnet (YIG) spheres, microwave cavities and a superconducting (SC) qubit. In the schemes, the YIGs are coupled to respective microwave cavities in resonant way, and the SC qubit is placed at the center of the cavities, which interacts with the cavities simultaneously. By exchanging the virtual photon, the cavities can indirectly interact in the far-detuning regime. Detailed protocols are presented to establish entanglement for two, three and arbitrary N magnons with reasonable fidelities.
