Sharp Localization Research Articles

Robust Effective Ground State in a Nonintegrable Floquet Quantum Circuit.

An external periodic (Floquet) drive is believed to bring any initial state to the featureless infinite temperature state in generic nonintegrable isolated quantum many-body systems in the thermodynamic limit, irrespective of the driving frequency Ω. However, numerical or analytical evidence either proving or disproving this hypothesis is very limited and the issue has remained unsettled. Here, we study the initial state dependence of Floquet heating in a nonintegrable kicked Ising chain of length up to L=30 with an efficient quantum circuit simulator, showing a possible counterexample: the ground state of the effective Floquet Hamiltonian is exceptionally robust against heating, and could stay at finite energy density even after infinitely many Floquet cycles, if the driving period is shorter than a threshold value. This sharp energy localization transition or crossover does not happen for generic excited states. The exceptional robustness of the ground state is interpreted by (i)its isolation in the energy spectrum and (ii)the fact that those states with L-independent ℏΩ energy above the ground state energy of any generic local Hamiltonian, like the approximate Floquet Hamiltonian, are atypical and viewed as a collection of noninteracting quasiparticles. Our finding paves the way for engineering Floquet protocols with finite driving periods realizing long-lived, or possibly even perpetual, Floquet phases by initial state design.

A finite element configuration interaction method for Wigner localization

The Wigner localization is an electron phase at low densities when the electrons are sharply localized around equilibrium positions. The simulation of the Wigner localization phenomenon requires careful treatment of the many-body correlations, as the electron-electron interaction dominates the system. This work proposes a numerical algorithm to study the electron ground states of the Wigner localized systems. The main features of our algorithm are three-fold: (i) a finite element discretization of the one-body space such that the sharp localization can be captured; (ii) a good initial state obtained by exploiting the strongly correlated limit; and (iii) a selected configuration interaction method by choosing the Slater determinants from (stochastic) gradients. Numerical experiments for some typical low-dimensional systems are provided to show the efficiency of our algorithm.

Opto-thermophoretic superlattice for atoms

We propose and study a dissipative optical superlattice for manipulation of resonant particles (atoms, ions and similar ones) located in a transparent buffer gas. Its working principle is based on the simultaneous effect of a longitudinal rectified gradient force and a transverse thermophoretic force in the field of collinear superposition of bichromatic cosine-Gaussian laser beams. As a result, there occurs a strong periodic stratification of the gas manifested in the accumulation and sharp localization of the resonant particles at the nodes of the superlattice and their cooling. Moreover, in the case of linearly polarized light beams, there appear circulating currents of the resonant particles (the so-called Brownian vortices) in the gas. Unlike the traditional dissipative optical lattices, in the superlattice under consideration, transverse particle confinement is implemented only due to the light-induced thermophoretic force, associated with the finiteness of the effective radius of the light beams.

Atomistic study on simultaneous achievement of partial crystallization and rejuvenated glassy structure in thermal process of metallic glasses

ABSTRACT The relaxation state and partial crystallization are crucial factors that affect the material properties of metallic glasses. Rejuvenation induces a less relaxed glass state and hence facilitates the control of the relaxation state. The rejuvenation and crystallization during thermal processing are associated closely with the phase changes of metallic glasses upon heating. Most nanocrystalline metallic glasses formed via conventional thermal annealing have a relaxed glassy matrix. In this molecular dynamics study, we investigate the feasibility of thermal processing to simultaneously realise both partial crystallization and rejuvenation using model alloy system. Dynamic mechanical analyses reveal relaxation behaviours and local deformation features of metallic glasses composed of a crystalline phase and a rejuvenated glass matrix. The crystalline phase increases the macroscopic shear stiffness of the composite model over a wide temperature range, whereas it does not significantly affect the internal friction of the rejuvenated glass matrix. In addition, dispersed nanocrystals suppress the development of sharp and concentrated shear localisation in the rejuvenated glass matrix. The simultaneous adjustment of the relaxation state and crystalline phase in the glass matrix is discussed from a viewpoint of the microstructure design of metallic glasses.

Global time evolution of concentrated vortex rings

We study the time evolution of an incompressible fluid with axial symmetry without swirl, assuming initial data such that the initial vorticity is very concentrated inside N small disjoint rings of thickness varepsilon and vorticity mass of the order of |log varepsilon |^{ -1}. When varepsilon rightarrow 0, we show that the motion of each vortex ring converges to a simple translation with constant speed (depending on the single ring) along the symmetry axis. We obtain a sharp localization of the vorticity support at time t in the radial direction, whereas we state only a concentration property in the axial direction. This is obtained for arbitrary (but fixed) intervals of time. This study is the completion of a previous paper [5], where a sharp localization of the vorticity support was obtained both along the radial and axial directions, but the convergence for varepsilon rightarrow 0 worked only for short times.

Topological properties and localization transition in a one-dimensional non-Hermitian lattice with a slowly varying potential

We explore the eigenenergy distribution, localization transition, and topological property of a one-dimensional non-Hermitian lattice with a slowly varying potential, which does not possess parity-time ($\mathcal{PT}$) symmetry. We found that, in contrast to $\mathcal{PT}$-symmetric systems whose eigenenergies can stay real until the $\mathcal{PT}$-symmetry breaking point, the eigenenergies in the present system are fully complex and their distribution in the complex plane depends on the parameters. As non-Hermiticity is introduced into the system, also depending on the parameters, the eigenstates may show a crossover behavior from fully extended to fully localized as non-Hermiticity is increased, or there will be a sharp localization transition at finite non-Hermiticity. Nevertheless, this non-Hermitian system is proven to be topologically trivial, thus we conclude that in general non-Hermitian systems, the localization transition is not always of a topological nature.

Diffusion-assisted ultrashort laser pulse induced photothermal growth of core-shell nanoparticles in polymer matrix.

Light-to-heat conversion that occurs when irradiating a metal nanoparticle within a polymer matrix with ultrashort laser pulses initiates photothermal destruction of dissolved precursor molecules just near the nanoparticle. Extracted elementary species deposit on the nanoparticle surface, forming a core-shell structure. We construct an approximate analytical model for this process. The necessary step here is the diffusion of the precursor molecules towards the nanoparticle surface, replacing the broken ones. This diffusion can be a limiting factor for the rate of the shell growth. However, we show that because of the sharp localization of the process the precursor diffusion can successfully supply the growing shell with elementary species at realistic values of the precursor diffusion coefficient if the sample is kept in viscoelastic state at a temperature near the glass transition between the laser pulses. The main restriction on the obtained shell thickness comes from the requirement of matrix stability during the laser processing. Taking this restriction into account, the model allows estimating reachable shell thicknesses depending on the kinetic parameters of the precursor destruction reaction. This paper relies on numerous publications on photo/laser-induced growth of homogeneous metal or semiconductor nanoparticles within polymer matrices; however, this type of growth for compound core-shell nanoparticles is studied for the first time, to our knowledge.

Local Form of Loss of Stability of Honeycomb Energy Absorber Plates

Landing devices perform the energy absorption function during the spacecraft motion. Precise analytical solution to the problem of stability of a lengthy plate with free edge exposed to the edge compressive load was obtained in order to analyze operation of the honeycomb materials used in structural elements absorbing the moving bodies energy. General solution analysis of the differential equation for a lengthy plate bending in the deflected position was carried out, and general solution is subjected to the boundary conditions corresponding to the loaded free edge. Critical load value and form of the loss of stability were determined. Critical load identified value was significantly lower than the critical load for a plate supported on the loaded edge. The loss of stability identified form was characterized by sharp deflection localization near the loaded edge and could create conditions for forming a local fold near the loaded edge. Obtained analytical solution was verified by comparing it with results of the similar numerical solution. Comparison performed revealed satisfactory agreement both in the critical load value and in the form of loss of stability for two solutions obtained by different methods. The results obtained could be used in designing energy absorbers made of honeycomb materials, as well as in other areas of technology

Topolectric circuits: Theory and construction

We highlight a general theory to engineer arbitrary Hermitian tight-binding lattice models in electrical LC circuits, where the lattice sites are replaced by the electrical nodes, connected to its neighbors and to the ground by capacitors and inductors. In particular, by supplementing each node with $n$ subnodes, where the phases of the current and voltage are the $n$ distinct roots of \emph{unity}, one can in principle realize arbitrary hopping amplitude between the sites or nodes via the \emph{shift capacitor coupling} between them. This general principle is then implemented to construct a plethora of topological models in electrical circuits, \emph{topolectric circuits}, where the robust zero-energy topological boundary modes manifest through a large boundary impedance, when the circuit is tuned to the resonance frequency. The simplicity of our circuit constructions is based on the fact that the existence of the boundary modes relies only on the Clifford algebra of the corresponding Hermitian matrices entering the Hamiltonian and not on their particular representation. This in turn enables us to implement a wide class of topological models through rather simple topolectric circuits with nodes consisting of only two subnodes. We anchor these outcomes from the numerical computation of the on-resonance impedance in circuit realizations of first-order ($m=1$), such as Chern and quantum spin Hall insulators, and second- ($m=2$) and third- ($m=3$) order topological insulators in different dimensions, featuring sharp localization on boundaries of codimensionality $d_c=m$. Finally, we subscribe to the \emph{stacked topolectric circuit} construction to engineer three-dimensional Weyl, nodal-loop, quadrupolar Dirac and Weyl semimetals, respectively displaying surface and hinge localized impedance.

Synthesizing multi-dimensional excitation dynamics and localization transition in one-dimensional lattices

The geometric dimensionality of a physical system significantly impacts its fundamental characteristics. While experiments are fundamentally limited to the maximum of three spatial dimensions, there is a growing interest in harnessing additional synthetic dimensions. In our work, we introduce a new paradigm for the experimental realization of excitation dynamics associated with many-dimensional systems. Crucially, it relies solely on static one-dimensional equivalent structures with judiciously tailored parameters to faithfully reproduce the same optical spectrum and density of states of the high-dimensional system to be represented. In order to showcase the capabilities of our approach, we fabricate 1D photonic lattices that exhibit the characteristic non-monotonic excitation decays associated with quantum walks in up to 7D square lattices. Furthermore, we find that a new type of bound state at the edge of the continuum emerges in higher-than-three dimensions and gives rise to a sharp localisation transition at defect sites. In a series of experiments, we implement the mapped equivalent lattices of up to 5D systems and observe an extreme increase of sensitivity with respect to the detuning of the respective anchor sites. Our findings demonstrate the feasibility and applicative potential of harnessing high-dimensional effects in planar photonics for ultra-sensitive switching or sensing. Notably, our general approach is by no means limited to optics, and can readily be adapted to a variety of other physical contexts, including cold atoms and superconducting qubits with exclusively nearest-neighbour interactions, promising to drive significant advances in different fields including quantum simulations and information processing.

Unconventional localization prior to wrinkles and controllable surface patterns of film/substrate bilayers through patterned cavities

Wrinkle formation followed by sharp strain localization is commonly observed in compressed stiff film/soft substrate systems. However, cavities or defects beneath the film may directly trigger the formation of local ridges and then folding configurations at a relatively small compressive strain, and a mixture of wrinkles and folds upon further compression. The morphological transition is different than those of defect-free substrates. Numerical simulations of continuously compressed bilayer with pre-patterned cavities are carried out to elucidate the transition mechanism of surface patterns. Parallel experiments of cavities-patterned bilayer prototypes by 3D-printing are also performed to validate the findings in simulations. A rich diversity of periodic surface topologies, including overall spreading waves, localizations, saw-like and co-existing features of folds and wrinkles can be obtained by varying the diameter, depth and spacing of cavities, which provides a potential approach to engineer various surface patterns for applications.

Existence of surface smectic states of liquid crystals

The Landau–de Gennes model of liquid crystals is a functional acting on wave functions (order parameters) and vector fields (director fields). In a specific asymptotic limit of the physical parameters, we construct critical points such that the wave function (order parameter) is localized near the boundary of the domain, and we determine a sharp localization of the boundary region where the wave function concentrates. Furthermore, we compute the asymptotics of the energy of such critical points along with a boundary energy that may serve in localizing the director field. In physical terms, our results prove the existence of a surface smectic state.

FUSION OF LANDSAT- 8 THERMAL INFRARED AND VISIBLE BANDS WITH MULTI-RESOLUTION ANALYSIS CONTOURLET METHODS

Abstract. Land surface temperature image is an important product in many lithosphere and atmosphere applications. This image is retrieved from the thermal infrared bands. These bands have lower spatial resolution than the visible and near infrared data. Therefore, the details of temperature variation can't be clearly identified in land surface temperature images. The aim of this study is to enhance spatial information in thermal infrared bands. Image fusion is one of the efficient methods that are employed to enhance spatial resolution of the thermal bands by fusing these data with high spatial resolution visible bands. Multi-resolution analysis is an effective pixel level image fusion approach. In this paper, we use contourlet, non-subsampled contourlet and sharp frequency localization contourlet transform in fusion due to their advantages, high directionality and anisotropy. The absolute average difference and RMSE values show that with small distortion in the thermal content, the spatial information of the thermal infrared and the land surface temperature images is enhanced.

Optical Tamm states in photonic structures made of inhomogeneous material

We demonstrate a tunable optical Tamm state at the interface between a photonic crystal (PC) and a film with non-uniformly varying refractive index. The optical Tamm state is associated with a sharp transmission peak and strong localization of the electric field. It is spectrally located inside the overlapping band gaps. The shift of the optical Tamm state is sensitive to the lattice constant of the inhomogeneous material. Our results provide an approach to tailor interface states in a controllable manner.

Faulting of natural serpentinite: Implications for intermediate-depth seismicity

The seismic potential of serpentinites at high pressure was investigated via deformation experiments on cored natural serpentinite samples, during which micro-seismicity was monitored by recording Acoustic Emissions (AEs). Deformation was performed at pressures of 3–5 GPa, using a Deformation-DIA device, and over a wide range of temperatures, both within and outside antigorite's stability field. Below 400 °C, serpentinite deformation involves “silent” semi-brittle mechanisms, even in cases where strain localization is observed. At high temperature (i.e., above 600 °C), despite conditions propitious to dehydration embrittlement (i.e., fast strain rates and reaction kinetics), joint deformation and dehydration lead to ductile shear, without generation of AEs. Brittle behavior was observed in a narrow temperature window ca. 500 °C. In this latter case, AEs are consistently observed upon faulting and extremely sharp strain localization is observed in recovered samples. The resulting microstructures are consistent with the inverse ductile-to-brittle transition proposed by Proctor and Hirth (2016) in antigorite. This may therefore be a source of seismicity in subducting slabs at mantle pressures and temperatures from 500 to 600 °C. However, the acoustic signal observed here is orders of magnitude weaker than what is obtained at low PT conditions with brittle failure, consistently with low radiation efficiency of serpentinite faulting (Prieto et al., 2013) and suggests that other mechanisms are responsible for large intermediate-depth earthquakes. In fact, the present results are in line with a recent study (Ferrand et al., 2017), that suggests that intermediate earthquakes are likely induced by mechanical instabilities due to dehydration in partly hydrated peridotites.

Metastable localization of diseases in complex networks.

We describe the phenomenon of localization in the epidemic susceptible-infective-susceptible model on highly heterogeneous networks in which strongly connected nodes (hubs) play the role of centers of localization. We find that in this model the localized states below the epidemic threshold are metastable. The longevity and scale of the metastable outbreaks do not show a sharp localization transition; instead there is a smooth crossover from localized to delocalized states as we approach the epidemic threshold from below. Analyzing these long-lasting local outbreaks for a random regular graph with a hub, we show how this localization can be detected from the shape of the distribution of the number of infective nodes.

Local microstructure evolution at shear bands in metallic glasses with nanoscale phase separation

At room temperature, plastic flow of metallic glasses (MGs) is sharply localized in shear bands, which are a key feature of the plastic deformation in MGs. Despite their clear importance and decades of study, the conditions for formation of shear bands, their structural evolution and multiplication mechanism are still under debate. In this work, we investigate the local conditions at shear bands in new phase-separated bulk MGs containing glassy nanospheres and exhibiting exceptional plasticity under compression. It is found that the glassy nanospheres within the shear band dissolve through mechanical mixing driven by the sharp strain localization there, while those nearby in the matrix coarsen by Ostwald ripening due to the increased atomic mobility. The experimental evidence demonstrates that there exists an affected zone around the shear band. This zone may arise from low-strain plastic deformation in the matrix between the bands. These results suggest that measured property changes originate not only from the shear bands themselves, but also from the affected zones in the adjacent matrix. This work sheds light on direct visualization of deformation-related effects, in particular increased atomic mobility, in the region around shear bands.

Image Denoising with Trivariate Shrinkage Based on Sharp Frequency Localization Contourlet

Image Denoising with Trivariate Shrinkage Based on Sharp Frequency Localization Contourlet

Breast Cancer Diagnosis System via Contourlet Transform with Sharp Frequency Localization and Least Squares Support Vector Machines

Breast Cancer Diagnosis System via Contourlet Transform with Sharp Frequency Localization and Least Squares Support Vector Machines

Nonparametric Denoising Methods Based on Contourlet Transform with Sharp Frequency Localization: Application to Low Exposure Time Electron Microscopy Images

Image denoising is a very important step in cryo-transmission electron microscopy (cryo-TEM) and the energy filtering TEM images before the 3D tomography reconstruction, as it addresses the problem of high noise in these images, that leads to a loss of the contained information. High noise levels contribute in particular to difficulties in the alignment required for 3D tomography reconstruction. This paper investigates the denoising of TEM images that are acquired with a very low exposure time, with the primary objectives of enhancing the quality of these low-exposure time TEM images and improving the alignment process. We propose denoising structures to combine multiple noisy copies of the TEM images. The structures are based on Bayesian estimation in the transform domains instead of the spatial domain to build a novel feature preserving image denoising structures; namely: wavelet domain, the contourlet transform domain and the contourlet transform with sharp frequency localization. Numerical image denoising experiments demonstrate the performance of the Bayesian approach in the contourlet transform domain in terms of improving the signal to noise ratio (SNR) and recovering fine details that may be hidden in the data. The SNR and the visual quality of the denoised images are considerably enhanced using these denoising structures that combine multiple noisy copies. The proposed methods also enable a reduction in the exposure time.