arXiv subjects

R. Wang

Publications and source records attributed to R. Wang.

At least 19 recordsLinked to original sources

arXiv2026

Floquet-Sambe Bottleneck and Frequency-Selective Localization in a Driven Synthetic Spin Chain

We study a finite Floquet chain in which a uniform nearest-neighbor hopping coexists with a periodically rotating, \textrm{SU(2)}-dictated spin-assisted hopping profile. The resulting coupling is spatially inhomogeneous -- weakest at the chain boundaries and strongest in the bulk -- and produces a frequency-dependent Floquet-Sambe bottleneck. In the closed system, the mean inverse participation ratio (\textrm{MIPR}) of the Floquet eigenstates exhibits a striking nonmonotonic dependence on the driving frequency $\omega $: the states remain extended at both low and high frequencies, but become maximally localized at an intermediate frequency. We demonstrate that this localization maximum occurs at $\omega _{\mathrm{peak}}\sim \mu _{-s}=\sqrt{% 2s}$, a scale controlled by the first boundary bottleneck. To connect these spectral properties to measurable transport, we construct an open-system Floquet-Sambe Green-function inverse participation ratio from the spatial density of the injected scattering state. This open-system diagnostic recovers the same nonmonotonic localization trend as its closed-system counterpart, with the peak shifted to higher frequencies by the static bandwidth and the lead self-energy. These findings establish the driven synthetic spin chain as a directly realizable, frequency-tunable platform for coherent information storage and retrieval, rooted in the interplay of Floquet-Sambe virtual channels, boundary-controlled localization, and frequency-selective transport in emerging multi-level superconducting circuit architectures.

cond-mat.mes-hall↗

arXiv2025

Wave-packet revival in a Floquet engineering quadratic potential system

We investigate the quantum dynamics of a one-dimensional tight-binding lattice driven by a spatially quadratic and time-periodic potential. Both Hermitian ($J_1 = J_2$) and non-Hermitian ($J_1 \neq J_2$) hopping regimes are analyzed. Within the framework of Floquet theory, the time-dependent Hamiltonian is mapped onto an effective static Floquet Hamiltonian, enabling a detailed study of the quasi-energy spectrum as function of the driving frequency $\omega$. By applying a gauge transformation, we find that critical frequencies $\omega_c$ emerge, at which nearly equidistant quasi-energy ladders appear, as revealed by a pronounced minimum in the normalized variance $\Delta(\omega)$ of the level spacings. This spectral regularity leads to robust periodic revivals and Bloch-like oscillations in the time evolution. Numerical simulations confirm that such coherent oscillations persist even in the non-Hermitian regime, where the periodic driving stabilizes an almost real and uniformly spaced quasi-energy ladder.

quant-ph↗

arXiv2025

ML-Driven Strong Lens Discoveries: Down to $\theta_E \sim 0.03''$ and $M_\mathrm{halo}< 10^{11} M_\odot$

We present results on extending the strong lens discovery space down to much smaller Einstein radii ($\theta_E\lesssim0.03''$) and much lower halo mass ($M_\mathrm{halo}<10^{11}M_\odot$) through the combination of JWST observations and machine learning (ML) techniques. First, we forecast detectable strong lenses with JWST using CosmoDC2 as the lens catalog, and a source catalog down to 29th magnitude. By further incorporating the VELA hydrodynamical simulations of high-redshift galaxies, we simulate strong lenses. We train a ResNet on these images, achieving near-100\% completeness and purity for ``conventional" strong lenses ($\theta_E\gtrsim 0.5''$), applicable to JWST, HST, the Roman Space Telescope and Euclid VIS. For the first time, we also search for very low halo mass strong lenses ($M_{halo}<10^{11}M_\odot$) in simulations, with $\theta_E\ll 0.5''$, down to the best resolution ($0.03''$) and depth (10,000~sec) limits of JWST using ResNet. A U-Net model is employed to pinpoint these small lenses in images, which are otherwise virtually impossible for human detection. Our results indicate that JWST can find $\sim 17$/deg$^2$ such low-halo-mass lenses, with the locations of $\sim 1.1$/deg$^2$ of these detectable by the U-Net at $\sim100$\% precision (and $\sim 7.0$/deg$^2$ at a 99.0\% precision). To validate our model for finding ``conventional" strong lenses, we apply it to HST images, discovering two new strong lens candidates previously missed by human classifiers in a crowdsourcing project (Garvin et al. 2022). This study demonstrates the (potentially ``superhuman") advantages of ML combined with current and future space telescopes for detecting conventional, and especially, low-halo-mass strong lenses, which are critical for testing CDM models.

astro-ph.CO↗

arXiv2025

Probing quantum phase transition in a staggered Bosonic Kitaev chain via layer-resolved localization-delocalization transition

The bosonic statistics, which allow for macroscopic multi-occupancy of single-particle states, pose significant challenges for analyzing quantum phase transitions in interacting bosonic systems, both analytically and numerically. In this work, we systematically investigate the non-Hermitian Bloch core matrix of a Hermitian staggered bosonic Kitaev chain, formulated within the Nambu framework. We derive explicit analytic conditions for the emergence of exceptional points (EPs) in the $4\times 4$ Bloch core matrix, with each EP marking the onset of complex-conjugate eigenvalue pairs. By mapping the full many-body Hamiltonian onto an effective tight-binding network in Fock-space and introducing layer-resolved inverse participation ratio, we demonstrate that these EPs coincide precisely with sharp localization--delocalization transitions of collective eigenstates. Comprehensive numerical analyses across hopping amplitudes, pairing strengths, and on-site potentials confirm that the EP of effective Hamiltonian universally capture the global many-body phase boundaries. Our results establish an analytically tractable, EP-based criterion for detecting critical behavior in interacting bosonic lattices, with direct relevance to photonic and cold-atom experimental platforms.

cond-mat.quant-gas↗

arXiv2024

Dynamic manifestation of exception points in a non-Hermitian continuous model with an imaginary periodic potential

Exceptional points (EPs) are distinct characteristics of non-Hermitian Hamiltonians that have no counterparts in Hermitian systems. In this study, we focus on EPs in continuous systems rather than discrete non-Hermitian systems, which are commonly investigated in both the experimental and theoretical studies. The non-Hermiticity of the system stems from the local imaginary potential, which can be effectively achieved through particle loss in recent quantum simulation setups. Leveraging the discrete Fourier transform, the dynamics of EPs within the low-energy sector can be well modeled by a Stark ladder system under the influence of a non-Hermitian tilted potential. To illustrate this, we systematically investigate continuous systems with finite imaginary potential wells and demonstrate the distinctive EP dynamics across different orders. Our investigation sheds light on EP behaviors, potentially catalyzing further exploration of EP phenomena across a variety of quantum simulation setups.

quant-ph↗

arXiv2024

A Primal Staggered Discontinuous Galerkin Method on Polytopal Meshes

This paper introduces a novel staggered discontinuous Galerkin (SDG) method tailored for solving elliptic equations on polytopal meshes. Our approach utilizes a primal-dual grid framework to ensure local conservation of fluxes, significantly improving stability and accuracy. The method is hybridizable and reduces the degrees of freedom compared to existing approaches. It also bridges connections to other numerical methods on polytopal meshes. Numerical experiments validate the method's optimal convergence rates and computational efficiency.

math.NA↗

arXiv2024

A Multi-station Meteor Monitoring (M$^3$) System. II. system upgrade and a pathfinder network

Meteors are important phenomenon reflecting many properties of interplanetary dust particles. The study of their origin, mass distribution, and orbit evolution all require large data volume, which can only be obtained using large meteor networks. After meteor networks in Europe and America, we present our designs and upgrades of a proposing network in China. The new designs are mainly aimed for facilitating data gathering process. Each of the newly designed meteor stations now can support up to 4 cameras to cover the full sky. Newer version of meteor station software now works as an integral system, which can streamline the process of detecting, measuring and uploading meteors. We have built a meteor data platform to store, process and display the meteor data automatically. The software and data platform are designed to be easy to learn and use, so it can attract more people to join and operate meteor stations. Four stations are installed as the first phase of the network, and during the operation in 10 months, the network detected 8,683 orbits, and we find that half of the orbits can be related to established meteoroid streams. The statistical analysis of sporadic meteoroids shows a bimodal distribution of the velocities, which coincides with previous studies. The distribution of Tisserand parameters, $T_j$, shows the two peaks at $T_j=0$ and 3, indicating the different orbits of parent bodies (isotropic and ecliptic), which are divided by $T_j=2$. The falling trajectory of a meteorite was also predicted using observational data of the network. We are currently expanding the network, and in the future we will carry out detailed analysis of the key parameters of the distribution of the meteoroids.

astro-ph.IM↗

arXiv2024

Performance assessment of the HERD calorimeter with a photo-diode read-out system for high-energy electron beams

The measurement of cosmic rays at energies exceeding 100 TeV per nucleon is crucial for enhancing the understanding of high-energy particle propagation and acceleration models in the Galaxy. HERD is a space-borne calorimetric experiment that aims to extend the current direct measurements of cosmic rays to unexplored energies. The payload is scheduled to be installed on the Chinese Space Station in 2027. The primary peculiarity of the instrument is its capability to measure particles coming from all directions, with the main detector being a deep, homogeneous, 3D calorimeter. The active elements are read out using two independent systems: one based on wavelength shifter fibers coupled to CMOS cameras, and the other based on photo-diodes read-out with custom front-end electronics. A large calorimeter prototype was tested in 2023 during an extensive beam test campaign at CERN. In this paper, the performance of the calorimeter for high-energy electron beams, as obtained from the photo-diode system data, is presented. The prototype demonstrated excellent performance, e.g., an energy resolution better than 1% for electrons at 250 GeV. A comparison between beam test data and Monte Carlo simulation data is also presented.

physics.ins-det↗

arXiv2024

A Multi-station Meteor Monitoring (M$^3$) System. I. Design and Testing

Meteors carry important and indispensable information about the interplanetary environment, which can be used to understand the origin and evolution of our solar system. We have developed a Multi-station Meteor Monitoring ($\rm M^3$) system that can observe almost the entire sky and detect meteors automatically, and it determines their trajectories. They are highly extensible to construct a large-scale network. Each station consists of a waterproof casing, a wide field-of-view lens with a CMOS camera, and a supporting computer. The camera has a built-in GPS module for accurately timing the meteoroid entry into the atmosphere (accurate to 1 $\mu$s), which is the most prominent characteristic compared with other existing meteor monitoring devices. We have also developed a software package that can efficiently identify and measure meteors appearing in the real-time video stream and compute the orbits of meteoroids in the solar system via multi-station observations. During the Geminid meteor shower in 2021, the M$^3$ system was tested at two stations ($\sim$55 km apart) in the suburbs of Beijing. The test results show that the astrometric accuracy is about 0.3-0.4 arcmin. About 800 meteors were detected by these two stations. A total of 473 meteors have their orbits calculated by our software, and 377 of them belong to the Geminid meteoroid stream. Our M$^3$ system will be further tested and upgraded, and it will be used to construct a large monitoring network in China in the future.

astro-ph.IM↗

arXiv2024

In-plane dielectric constant and conductivity of confined water

Water is essential for almost every aspect of life on our planet and, unsurprisingly, its properties have been studied in great detail. However, disproportionately little remains known about the electrical properties of interfacial and strongly confined water where its structure deviates from that of bulk water, becoming distinctly layered. The structural change is expected to affect water's conductivity and particularly its polarizability, which in turn modifies intermolecular forces that play a crucial role in many physical and chemical processes. Here we use scanning dielectric microscopy to probe the in-plane electrical properties of water confined between atomically flat surfaces separated by distances down to 1 nm. For confinement exceeding a few nm, water exhibits an in-plane dielectric constant close to that of bulk water and its proton conductivity is notably enhanced, gradually increasing with decreasing water thickness. This trend abruptly changes when the confined water becomes only a few molecules thick. Its in-plane dielectric constant reaches giant, ferroelectric-like values of about 1,000 whereas the conductivity peaks at a few S/m, close to values characteristic of superionic liquids. We attribute the enhancement to strongly disordered hydrogen bonding induced by the few-layer confinement, which facilitates both easier in-plane polarization of molecular dipoles and faster proton exchange. This insight into the electrical properties of nanoconfined water is important for understanding many phenomena that occur at aqueous interfaces and in nanoscale pores.

cond-mat.mes-hall↗

arXiv2024

On the critical competition between singlet exciton decay and free charge generation in non-fullerene-based organic solar cells with low energetic offsets

In this era of non-fullerene acceptor (NFA) based organic solar cells, reducing voltage losses while maintaining high photocurrents is the holy grail of current research. Recent focus lies in understanding the manifold fundamental mechanisms in organic blends with minimal energy offsets - particularly the relationship between ionization energy offset ({\Delta}IE) and free charge generation. We quantitatively probe this relationship in multiple NFA-based blends by mixing Y5 and Y6 NFAs with PM6 of varying molecular weights, covering a 15% to 1% power conversion efficiency (PCE) range and a progression of {\Delta}IE. Spectroelectrochemistry reveals a critical {\Delta}IE of approximately 0.3 eV, below which the PCE sharply declines. Transient absorption spectroscopy consistently reveals that a smaller {\Delta}IE slows the dissociation of the NFA's local singlet exciton (LE) into free charges, albeit restorable by an electric field. Bias-dependent time delayed collection experiments quantify the free charge generation efficiency, while photoluminescence quantum efficiency measurements assess photocurrent loss from LE decay. Combined with transient photoluminescence experiments, we find that the decay of singlet excitons is the primary competition to free charge generation in low-offset NFA-based organic solar cells, with neither noticeable losses from charge-transfer (CT) decay nor evidence for LE-CT hybridization. Our experimental data align with Marcus theory calculations, supported by density functional theory simulations, for zero-field free charge generation and exciton decay efficiencies. We find that efficient photocurrent generation generally requires that the CT state is located below the LE, but that this restriction is lifted in systems with a small reorganization energy for charge transfer.

cond-mat.mtrl-sci↗

arXiv2024

Revealing the Microscopic Mechanism of Elementary Vortex Pinning in Superconductors

Vortex pinning is a crucial factor that determines the critical current of practical superconductors and enables their diverse applications. However, the underlying mechanism of vortex pinning has long been elusive, lacking a clear microscopic explanation. Here using high-resolution scanning tunneling microscopy, we studied single vortex pinning induced by point defect in layered FeSe-based superconductors. We found the defect-vortex interaction drives low-energy vortex bound states away from EF, creating a "mini" gap that effectively lowers the system energy and enhances pinning. By measuring the local density-of-states, we directly obtained the elementary pinning energy and estimated the pinning force via the spatial gradient of pinning energy. The results are consistent with bulk critical current measurement. Furthermore, we show that a general microscopic quantum model incorporating defect-vortex interaction can naturally capture our observation. It suggests that the local pairing near pinned vortex core is actually enhanced compared to unpinned vortex, which is beyond the traditional understanding that non-superconducting regions pin vortices. Our study thus unveils a general microscopic mechanism of vortex pinning in superconductors, and provides insights for enhancing the critical current of practical superconductors.

cond-mat.supr-con↗

arXiv2024

Extended Donnan model for ion partitioning in charged nanopores

Membranes consist of pores and the walls of these pores are often charged. In contact with an aqueous solution, the pores fill with water and ions migrate from solution into the pores until chemical equilibrium is reached. The distribution of ions between outside and pore solution is governed by a balance of chemical potential, and the resulting model is called a Donnan theory, or Donnan equation. Including a partitioning coefficient that does not depend on salt concentration results in an extended Donnan equation `of the first kind'. Recently, an electrostatic model was proposed for ions in a pore based on the arrangement of ions around strands of polymer charge, including also ion activity coefficients in solution. That framework leads to an extended Donnan equation `of the second kind', which has extra factors depending on ion concentrations in the pores and salt concentration in solution. In the present work, we set up another Donnan model of the second kind by evaluating the Coulombic interactions of ions in a cylindrical pore, including the interaction of ions with the charged pore walls and between the ions. We assume that counterions are near the pore wall while coions distribute over the center region. Starting from a complete analysis, we arrive at an elegant expression for the chemical potential of ions in such a pore. This expression depends on coion concentration, pore size, and other geometrical factors, but there is no additional dependence on counterion concentration and charge density. This model predicts the Coulombic contribution to the chemical potential in the pore to be small, much smaller than predicted by the electrostatic model from literature. Instead, we predict that up to around 1 M salt concentration, activity effects of ions in solution are more important.

physics.chem-ph↗

arXiv2023

Solar neutrino measurements using the full data period of Super-Kamiokande-IV

An analysis of solar neutrino data from the fourth phase of Super-Kamiokande~(SK-IV) from October 2008 to May 2018 is performed and the results are presented. The observation time of the data set of SK-IV corresponds to $2970$~days and the total live time for all four phases is $5805$~days. For more precise solar neutrino measurements, several improvements are applied in this analysis: lowering the data acquisition threshold in May 2015, further reduction of the spallation background using neutron clustering events, precise energy reconstruction considering the time variation of the PMT gain. The observed number of solar neutrino events in $3.49$--$19.49$ MeV electron kinetic energy region during SK-IV is $65,443^{+390}_{-388}\,(\mathrm{stat.})\pm 925\,(\mathrm{syst.})$ events. Corresponding $\mathrm{^{8}B}$ solar neutrino flux is $(2.314 \pm 0.014\, \rm{(stat.)} \pm 0.040 \, \rm{(syst.)}) \times 10^{6}~\mathrm{cm^{-2}\,s^{-1}}$, assuming a pure electron-neutrino flavor component without neutrino oscillations. The flux combined with all SK phases up to SK-IV is $(2.336 \pm 0.011\, \rm{(stat.)} \pm 0.043 \, \rm{(syst.)}) \times 10^{6}~\mathrm{cm^{-2}\,s^{-1}}$. Based on the neutrino oscillation analysis from all solar experiments, including the SK $5805$~days data set, the best-fit neutrino oscillation parameters are $\rm{sin^{2} \theta_{12,\,solar}} = 0.306 \pm 0.013 $ and $\Delta m^{2}_{21,\,\mathrm{solar}} = (6.10^{+ 0.95}_{-0.81}) \times 10^{-5}~\rm{eV}^{2}$, with a deviation of about 1.5$\sigma$ from the $\Delta m^{2}_{21}$ parameter obtained by KamLAND. The best-fit neutrino oscillation parameters obtained from all solar experiments and KamLAND are $\sin^{2} \theta_{12,\,\mathrm{global}} = 0.307 \pm 0.012 $ and $\Delta m^{2}_{21,\,\mathrm{global}} = (7.50^{+ 0.19}_{-0.18}) \times 10^{-5}~\rm{eV}^{2}$.

hep-ex↗

arXiv2023

Constraining nucleon effective masses with flow and stopping observables from the S$\pi$RIT experiment

Properties of the nuclear equation of state (EoS) can be probed by measuring the dynamical properties of nucleus-nucleus collisions. In this study, we present the directed flow ($v_1$), elliptic flow ($v_2$) and stopping (VarXZ) measured in fixed target Sn + Sn collisions at 270 AMeV with the S$\pi$RIT Time Projection Chamber. We perform Bayesian analyses in which EoS parameters are varied simultaneously within the Improved Quantum Molecular Dynamics-Skyrme (ImQMD-Sky) transport code to obtain a multivariate correlated constraint. The varied parameters include symmetry energy, $S_0$, and slope of the symmetry energy, $L$, at saturation density, isoscalar effective mass, $m_{s}^*/m_{N}$, isovector effective mass, $m_{v}^{*}/m_{N}$ and the in-medium cross-section enhancement factor $\eta$. We find that the flow and VarXZ observables are sensitive to the splitting of proton and neutron effective masses and the in-medium cross-section. Comparisons of ImQMD-Sky predictions to the S$\pi$RIT data suggest a narrow range of preferred values for $m_{s}^*/m_{N}$, $m_{v}^{*}/m_{N}$ and $\eta$.

nucl-ex↗

arXiv2023

The New Small Wheel electronics

The increase in luminosity, and consequent higher backgrounds, of the LHC upgrades require improved rejection of fake tracks in the forward region of the ATLAS Muon Spectrometer. The New Small Wheel upgrade of the Muon Spectrometer aims to reduce the large background of fake triggers from track segments that are not originated from the interaction point. The New Small Wheel employs two detector technologies, the resistive strip Micromegas detectors and the "small" Thin Gap Chambers, with a total of 2.45 Million electrodes to be sensed. The two technologies require the design of a complex electronics system given that it consists of two different detector technologies and is required to provide both precision readout and a fast trigger. It will operate in a high background radiation region up to about 20 kHz/cm$^{2}$ at the expected HL-LHC luminosity of $\mathcal{L}$=7.5$\times10^{34}$cm$^{-2}$s$^{-1}$. The architecture of the system is strongly defined by the GBTx data aggregation ASIC, the newly-introduced FELIX data router and the software based data handler of the ATLAS detector. The electronics complex of this new detector was designed and developed in the last ten years and consists of multiple radiation tolerant Application Specific Integrated Circuits, multiple front-end boards, dense boards with FPGA's and purpose-built Trigger Processor boards within the ATCA standard. The New Small Wheel has been installed in 2021 and is undergoing integration within ATLAS for LHC Run 3. It should operate through the end of Run 4 (December 2032). In this manuscript, the overall design of the New Small Wheel electronics is presented.

hep-ex↗

arXiv2022

Isoscaling in central Sn+Sn collisions at 270 MeV/u

Experimental information on fragment emissions is important in understanding the dynamics of nuclear collisions and in the development of transport model simulating heavy-ion collisions. The composition of complex fragments emitted in the heavy-ion collisions can be explained by statistical models, which assume that thermal equilibrium is achieved at collision energies below 100 MeV/u. Our new experimental data together with theoretical analyses for light particles from Sn+Sn collisions at 270 MeV/u, suggest that the hypothesis of thermal equilibrium breaks down for particles emitted with high transfer momentum. To inspect the system's properties in such limit, the scaling features of the yield ratios of particles from two systems, a neutron-rich system of ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ and a nearly symmetric system of ${}^{108}\mathrm{Sn}+{}^{112}\mathrm{Sn}$, are examined in the framework of the statistical multifragmentation model and the antisymmetrized molecular dynamics model. The isoscaling from low energy particles agree with both models. However the observed breakdown of isoscaling for particles with high transverse momentum cannot be explained by the antisymmetrized molecular dynamics model.

nucl-ex↗

arXiv2022

Neutron Tagging following Atmospheric Neutrino Events in a Water Cherenkov Detector

We present the development of neutron-tagging techniques in Super-Kamiokande IV using a neural network analysis. The detection efficiency of neutron capture on hydrogen is estimated to be 26%, with a mis-tag rate of 0.016 per neutrino event. The uncertainty of the tagging efficiency is estimated to be 9.0%. Measurement of the tagging efficiency with data from an Americium-Beryllium calibration agrees with this value within 10%. The tagging procedure was performed on 3,244.4 days of SK-IV atmospheric neutrino data, identifying 18,091 neutrons in 26,473 neutrino events. The fitted neutron capture lifetime was measured as 218 \pm 9 \mu s.

hep-ex↗