arXiv subjects

Xiaoxiao Wu

Publications and source records attributed to Xiaoxiao Wu.

At least 19 recordsLinked to original sources

arXiv2026

Orthogonal Flatbands-Enabled Robust Fano Resonances through Brillouin-Zone Folding

Fano resonances based on coherent interference between localized Lorentz modes and Fabry-Perot radiation continua have been widely explored for microwave metamaterial sensors, filters, and photonic devices. However, conventional Fano metasurfaces suffer from angular dispersion and polarization-dependent spectral variations, limiting robustness under dynamic illumination. Here, we propose a band-folding-enabled flatband engineering strategy to realize robust Fano resonances in a planar microwave metasurface with a 2x2 enlarged cell of orthogonally arranged H-shaped metallic resonators. The enlarged cell induces Brillouin-zone folding, generating a nearly dispersionless flatband near 15.3 GHz with suppressed momentum dependence and enhanced photonic confinement. This flatband state provides a high-Q localized resonance strongly coupled to the FP radiation continuum, producing a stable asymmetric Fano response. Furthermore, the orthogonal resonator configuration supports two polarization-decoupled dipole modes with comparable excitation efficiency, reducing polarization-induced spectral distortion. Near-field measurements and simulations verify localized flatband features, while far-field experiments demonstrate stable Fano responses under oblique incidence from 0° to 30° with minor resonance variation. A temporal coupled-mode theory model is developed to quantitatively describe Fano spectral evolution under different illumination conditions. This work establishes a flatband-mediated route toward robust microwave Fano metasurfaces and offers a general strategy for stable resonant photonic device design.

physics.optics↗

arXiv2026

Fleets Need a Context Plane: Rethinking Cooperative Perception for Autonomous Drones

Cooperative perception allows a drone fleet to combine observations from multiple viewpoints. However, existing systems typically fix their feature-sharing policies at design time or adapt to only one context signal. This is a poor fit for aerial fleets, whose missions, bandwidth, formation geometry, and scene coverage can change during flight. We quantify the cost of context-blind sharing on UAV3D by controlling feature exchange at evaluation time using a released DiscoNet checkpoint, without retraining. Mission-aware sharing matches full-sharing accuracy while using only 5-10% of the bytes. The best tested peer selection policy changes with the byte budget, and choosing the wrong policy loses up to 7.7 AP. Moreover, under a constrained budget, two policies with the same full-scene accuracy differ by 5.9 AP within the mission region, showing that multiple context axes must be considered jointly. We therefore propose the context plane, a bounded, structured interface for runtime context. Each drone publishes a descriptor of at most 1 KB at 10 Hz, and lightweight, replaceable policies use the fleet context to decide what each drone computes, shares, and fuses. Existing sharing schemes become fixed policies within this interface. In our ROS 2 prototype on a Jetson AGX Orin, the context plane uses approximately 0.01% of the data-plane bandwidth, and each policy decision takes 0.10 ms. These results show that an explicit context interface can support low-overhead runtime adaptation without modifying or retraining the perception model.

cs.RO↗

arXiv2026

BioZKFHE: Scalable Encrypted Biometric Identification via Verifiable Homomorphic Similarity Evaluation

Large-scale biometric identification in outsourced settings requires two properties simultaneously: biometric templates and queries must remain protected during computation, and the encrypted similarity outputs produced by an untrusted compute node must be verifiably correct before any application result is released. Existing FHE-based biometric systems primarily address confidentiality, while practical verifiability introduces two bottlenecks in the underlying encrypted 1:N matching layer: rotation- and bandwidth-heavy similarity evaluation and the high cost of proving repeated homomorphic similarity traces. We present BioZKFHE, a framework for scalable encrypted biometric identification via verifiable homomorphic similarity evaluation that combines BGV homomorphic computation with committee-mediated proof opening/decryption and smart-contract verification of opened proof batches. To reduce encrypted storage and avoid rotation-heavy encrypted 1:N matching, we propose Single-Coefficient Multi-Value (SCMV) packing, which binds multiple quantized embedding values into each plaintext entry through base-T expansion. To make proof generation practical, we propose Parallelizable and Verifiable Similarity Computation (PVSC), which exploits the Double-CRT execution structure of BGV to decompose each blockwise similarity trace into parallel proof instances that are opened and checked before result release. Under standard lattice assumptions and explicit committee/verifier assumptions, we analyze recoverability, noise growth, confidentiality, encrypted-output integrity, and finalized-result integrity. Experiments on FaceNet and MobileFaceNet show near-lossless biometric utility, up to 67 percent encrypted-storage reduction, and about 22 to 44 seconds end-to-end proof-verified runtime for 10k to 40k templates.

cs.CR↗

arXiv2026

Dirac-vortex modes beyond the continuum limit

Dirac-vortex modes (DVMs) in Kekule-modulated lattices provide a topological route to wave confinement and are commonly described by the continuum Jackiw-Rossi model, in which the initial phase acts as a redundant gauge degree of freedom and does not affect observables of the mode. Here we show that this picture breaks down in discrete lattices when the complex mass texture that induces the DVMs no longer satisfies the slowly varying envelope approximation. In this regime, lattice discreteness turns the initial phase into a physically observable parameter that shifts the DVM center. By further introducing a sublattice-antisymmetric perturbation, we convert this phase-dependent center motion into a continuous spectral response of the DVM, enabling its frequency tuning across nearly the entire topological bandgap. Our simulation and experimental results agree well with a revised continuum model accounting for the mode-center motion. Within this perturbative framework, the model shows that the frequency shift exhibits a sinusoidal-like dependence on the initial phase. These findings reveal initial phase-sensitivity of the DVMs realized in lattices, an important and basic feature absent from the ideal continuum Jackiw-Rossi model, and demonstrate initial phase engineering as a potential pathway towards reconfigurable photonic devices.

physics.optics↗

arXiv2026

Chiral Landau levels induced by two in-plane pseudomagnetic fields in underwater acoustic metamaterials

The chiral zeroth Landau levels (LLs) constitute topologically protected bulk states that enable robust control of acoustic wave propagation. Given the central role of underwater acoustics in marine engineering, realizing such Landau-level physics in underwater acoustic systems is highly desirable. Nevertheless, existing studies have primarily been limited to airborne acoustic systems, and the implementation of chiral zeroth LLs in underwater acoustics remains a challenge due to the unavoidable fluid-solid interactions. In this study, we realize two kinds of chiral LLs in an open underwater spoof surface acoustic wave (SSAW) platform by introducing two perpendicular in-plane artificial pseudomagnetic fields (PMFs), oriented along the x and y directions, respectively, and reveal that scalar acoustic fields in water and vectorial elastic vibrations in solids can be jointly manipulated within a unified framework. Specifically, by strategically opening bandgaps at the Dirac points, position-dependent effective mass terms are introduced into the Dirac Hamiltonians, thereby synthesizing two in-plane PMFs. This results in the emergence of chiral LLs, which is confirmed both numerically and experimentally. The unidirectional propagation of the chiral LLs and their robustness against defects are also demonstrated. In addition, we achieve flexible manipulation of underwater ultrasonic energy carried by SSAWs, including beam splitting and arbitrary wave steering. Dual-band chiral LLs are also observed in small-scale underwater topological metamaterials. Our work provides a new route toward SSAW-based underwater ultrasonic control, opening opportunities for multiband underwater acoustic signal processing and detection, as well as underwater acoustic energy harvesting.

physics.app-ph↗

arXiv2026

Spatiotemporal Optical Vortices From All-Dielectric Bilayer Metagratings

Spatiotemporal optical vortices (STOVs) carry transverse orbital angular momentum within the space-time domain, rendering them powerful tools for constructing high-dimensional and quantum optical fields. However, most existing approaches rely on highly lossy metallic structures or complex pulse-shaping systems. Here, we propose an all-dielectric route to STOV generation based on symmetry-protected bound states in the continuum (BICs) in a bilayer metagrating and provide proof-of-concept validation of its key momentum-frequency signatures. By simply introducing a lateral shift between the upper and lower layers of the vertical slots on the dielectric metagrating, the Γ-point BIC transforms into a quasi-BIC (qBIC) with momentum-dependent directional radiation and asymmetric coupling. This qBIC further leads to an isolated zero-transmission dip associated with a clear phase singularity and branch cut in the momentum-frequency response, enabling stable STOV generation under excitation by a spatiotemporal Gaussian pulse. The multipole analysis of the qBIC reveals the key role of the Kerker-type interference between its electric and magnetic dipoles and associated asymmetric coupling in the STOV generation. Experimentally, free-space transmission measurements reveal a transmission zero and a branch cut that agree excellently with theoretical analysis. Therefore, our work provides an experimentally validated, scalable route for manipulating spatiotemporal optical fields on low-loss all-dielectric metasurfaces via only gliding offsets, with potential applications in directional coupling of quantum light sources and spatiotemporal shaping of single-photon wave packets.

physics.optics↗

arXiv2026

Agentic Trading: When LLM Agents Meet Financial Markets

A growing body of work explores how Large Language Models (LLMs) can be embedded in trading systems as agents that perceive market information, retrieve context, reason about decisions, emit tradable actions, and adapt under market feedback. This paper reframes LLM-based trading agents as expert-system decision pipelines and presents an audit-oriented evidence map of 77 included studies in a protocol-coded snapshot screened through 2026-03-09. A primary empirical subset (n=19) satisfies the minimum boundary of Action Output plus Closed-Loop Evaluation; the remaining 58 included studies are retained as background and design context. The central empirical finding is protocol incomparability: within the primary subset, only 2/19 studies report extractable time-consistent split protocols, 1/19 reports an explicit transaction-cost model, 1/19 documents universe or survivorship handling, 11/19 report execution timing or semantics, 15/19 are coded as R0, and no study reaches R3 reproducibility. We therefore use Architecture-Capability-Adaptation as a working analytical lens rather than a validated taxonomy, and we foreground the evidence ledger, reproducibility audit, and reporting checklist as the main contributions. The resulting survey shows that architectural experimentation is expanding rapidly, while comparable evaluation protocols, execution semantics, and reproducible artifacts remain the field's immediate bottlenecks.

cs.AI↗

arXiv2026

Unveiling spin-orbital angular momentum locking in photonic Dirac vortex cavities

Dirac vortices, originally studied in quantum field theories to predict localized zero-energy modes, were recently realized in photonics, leading to Dirac vortex cavities. With topological protection, Dirac vortex cavities offer robust single-mode large-area localized modes appealing for high-performance micro-lasers and other applications. As a spectrally-isolated single mode, the radiation of a Dirac vortex cavity mode was believed as having vanishing orbital angular momentum due to time-reversal symmetry. Here, we report the direct observation of orbital angular momentum radiation of a Dirac vortex cavity through spin-resolved measurements. Remarkably, we confirm the spin-orbital angular momentum locking in such radiation due to the spin-valley locking and inter-valley couplings. We demonstrate that the spin-orbital angular momentum locking is controlled by the chirality of the Kekulé modulation and propose design schemes for arbitrary-order single-mode OAM radiation.

physics.optics↗

arXiv2025

Giant and Rapidly Switching Intrinsic Chirality Enabled by Toroidal Quasi-Bound States in the Continuum

Circular dichroism (CD), arising from spin-selective light-matter interactions controlled by chirality, is critical for advanced applications such as chiral imaging and ultrasensitive biosensing. However, CD of chiral natural materials is inherently constrained owing to molecular symmetry and thermodynamic stability. Recently, artificially engineered metasurfaces incorporating chiral quasi-bound states in the continuum (Q-BICs) have emerged as a promising solution, which enables near-unity CD responses. However, their current designs heavily rely on complex three-dimensional geometries, posing significant challenges for integration with planar on-chip platforms. To address the stringent challenges, we demonstrate a truly planar metasurface that achieves giant intrinsic chiral responses by utilizing a chiral Q-BIC dominated by out-of-plane toroidal dipoles (Tz). With deep-subwavelength (λ/20) thickness, our metasurface exhibits outstanding intrinsic CD values in both simulations (>0.90) and experiments (~0.80). Moreover, in contrast to previous electric or magnetic chiral Q-BICs, the toroidal Q-BIC produces a rapidly switching CD response - transitioning sharply between positive and negative giant CD values within ~0.2 GHz, and the switching is highly sensitive to small oblique incidence of opposite angles. Therefore, our scheme provides a planar platform for studying chiral light-matter interactions involving toroidal dipoles, important for future development of polarization- and angle-sensitive photonic and optoelectronic devices.

physics.optics↗

arXiv2025

Kirigami-based Flexible Metasurface with Reconfigurable Intrinsic Chirality from Zero to Near-unity

Chiral responses in electromagnetic metasurfaces are typically categorized as extrinsic, resulting from asymmetric interactions between the structure and incident waves, and intrinsic, arising from three-dimensional symmetry breaking of the unit cell. However, most existing metasurface designs target only one type of chirality and lack a unified, continuously tunable platform for broader chiroptical control. To address this limitation, the designed kirigami-based flexible metasurface is proposed for dynamic, continuous modulation of chirality, which expands the control scope to both extrinsic and intrinsic chiral responses within a single, reconfigurable platform. Initially, the unfolded metasurface exhibits extrinsic chirality under oblique incidence. By introducing well-designed kirigami-based cuts and folds, the metasurface transitions from a planar and achiral configuration to a three-dimensional chiral geometry that breaks the mirror symmetry, thereby exhibiting tunable intrinsic chirality and asymmetric extrinsic chirality. As the folding angle increases, the resulting deformation enables continuous tuning of the chiral response, with circular dichroism and its asymmetry under oblique incidences progressively increasing and reaching pronounced levels across the X-band. Our work provides a lightweight, easy-fabricated, and mechanically reconfigurable metasurface, which offers strong potential for future development in adaptive photonic systems and advanced chiroptical technologies.

physics.optics↗

arXiv2025

Hybrid Cavity from Tunable Coupling between Anapole and Fabry-Perot Resonance or Anti-resonance

Enhancing light-matter interactions depends critically on the ability to tailor photonic modes at subwavelength scales, and combining distinct resonant modes has shown remarkable potential unattainable by individual resonances alone. Despite recent advances in anapole metasurfaces for energy confinement and Fabry-Perot (FP) cavities for spectral control, their synergistic coupling and resulting opportunities remain largely unexplored due to challenges such as precise nanoscale assembly. Here, we demonstrate that embedding a terahertz (THz) anapole metasurface within a tunable FP cavity results in a hybrid cavity that demonstrates exotic properties as the anapole transitions between coupling to FP resonances and anti-resonances via cavity-length tuning. At room temperature, we observe ultrastrong coupling (> 30% of the anapole frequency) between anapoles and FP resonances, generating tunable-dispersion polaritons that blend favorable properties of both modes. Meanwhile, anapole spectrally aligns with FP anti-resonances, leading to weak coupling that narrows the linewidth of the anapole's transmission peak by two orders of magnitude and enhances its local density of states (LDOS) near the metasurface correspondingly. With exceptional capabilities including formation of polaritons and significant enhancement of LDOS, the hybrid cavity enables strong interaction with functional materials, paving the way for exploration of quantum optics, molecular sensing, and ultrafast nonlinear photonics.

physics.optics↗

arXiv2025

A Compact Dual-Beam Zeeman Slower for High-Flux Cold Atoms

We present a compact design of dual-beam Zeeman slower optimized for efficient production of cold atom applications. Traditional single-beam configurations face challenges from substantial residual atomic flux impacting downstream optical windows, resulting in increased system size, atomic deposition contamination, and a reduced operational lifetime. Our approach employs two oblique laser beams and a capillary-array collimation system to address these challenges while maintaining efficient deceleration. For rubidium ($^{87}$Rb), simulations demonstrate a significant increase in the fraction of atoms captured by a two-dimensional magneto-optical trap (2D-MOT) and nearly eliminate atom-induced contamination probability at optical windows, all within a compact Zeeman slower length of 44 cm. Experimental validation with Rb and Yb demonstrates highly efficient atomic loading within the same compact design. This advancement represents a substantial improvement for high-flux cold atom applications, providing reliable performance for high-precision metrology, quantum computation and simulation.

physics.atom-ph↗

arXiv2025

Direct Observation of Strongly Tilted Dirac Points at General Positions in the Reciprocal Space

Type-II Dirac points (DPs), which occur at the intersection of strongly tilted and touching energy bands, exhibit many intriguing physical phenomena fundamentally different from the non-tilted type-I counterparts. Over the past decade, their discovery has spurred extensive research into electronic systems and other Bloch-wave systems, such as photonic and phononic crystals. However, current studies typically focus on type-II DPs along high-symmetry directions in the first Brillouin zone (FBZ) under mirror symmetry conditions, which are highly restrictive and limit further investigations and applications. To overcome the stringent constraint, here we identify and demonstrate the emergence of type-II DPs at general positions inside the FBZ without requiring the mirror symmetry. The type-II DPs, being accidental degeneracies, are experimentally realized on a metacrystal slab with H-shaped metallic patterns. Our findings indicate that even in the absence of mirror symmetry, type-II DPs can emerge at designated locations inside the FBZ by simply rotating the H-shaped patterns and adjusting geometrical and physical parameters. Furthermore, based on the rotated type-II DPs, off-axis conical diffractions have been both realized and experimentally observed. Meanwhile, we discovered that during the rotation process, the type-II DPs transform into off-axis type-I DPs, but still strongly tilted, resulting in the emergence of negative refractions. Hence, the generic method we propose for inducing type-II or strongly tilted type-I DPs without the high-symmetry limitations opens potential avenues for related research. For example, the observed off-axis conical diffraction and negative refraction could inspire future development and applications in photonics and other Bloch-wave systems.

physics.optics↗

arXiv2025

Nonlocal Generation of Fano Resonance with No Symmetry Breaking in THz Hybrid Metasurfaces

Fano resonance, arising from the interference between a discrete resonance and a continuum of states, results in sharp and asymmetric line shapes and has significant applications in advanced photonic devices, particularly in sensing, filtering, and nonlinear optics. Nowadays, metasurfaces comprised of engineering microstructures play a crucial role in generation and manipulation of Fano resonance in photonics. However, current metasurfaces dominantly rely on local symmetry breaking of the microstructures to induce Fano resonances, which significant limits their tunability and scalable fabrication for practical applications. To address the challenge, a metal-dielectric hybrid metasurface is demonstrated to achieve nonlocal generation of Fano resonance with no symmetry breaking in the terahertz (THz) band. The Fano resonance, including its existence and peak frequency, is sensitively controlled by the thickness and dielectric constant of the dielectric layer, which is experimentally observed. Our analysis elucidates that the metallic layer with a pair of dumbbell holes leads to the band folding and coupling of guided modes within the dielectric layer. When the thickness or dielectric constant surpasses a critical value, the guided mode resonance falls below the diffraction limit, resulting in a unique nonlocal Fano resonance due to the interaction between the resonance and background transmission facilitated by dumbbell holes. Furthermore, the Fano transmission peak corresponds to an anapole excitation, revealed by multipole calculations. Benefiting from the ability to control the Fano resonance with no symmetry breaking, the proposed hybrid THz metasurface will advance broad applications in the fields of sensors, optical switches, and tunable filters.

physics.optics↗

arXiv2025

Twist-enabled Transmissive Metasurface with Co-polarized Geometric Phase

Metasurfaces have offered unprecedented control over electromagnetic (EM) waves across a wide range of frequency spectrum by manipulating their phase, amplitude, and polarization at subwavelength scales. Full wavefront control using metasurfaces requires 2π phase modulation, which is essential for advanced optical and photonic engineering. Common approaches, such as the Pancharatnam-Berry (PB) phases and resonant phases, face stringent limitations: PB phases essentially depend on circular polarization conversion, while resonant phases are inherently narrowband and require a complex design process. To overcome these challenges, we propose a broadband metasurface with a co-polarized transmissive geometric phase that achieves 2π phase coverage while conserving the circular polarization of incident EM waves. This co-polarized phase is enabled by a local twist angle between the upper and lower metallic patterns, forming a branch cut in the parameter space determined by the twist angle and frequency. The branch cut connects phase singularities of opposite chirality, ensuring broadband 2π phase coverage. We experimentally validate the presence of the branch cut and demonstrate broadband generation of arbitrary orbital angular momentum (OAM) for co-polarized output. Our approach provides a versatile method for designing broadband metasurfaces without altering circular polarizations, paving the way for development of compact optical and photonic devices.

physics.optics↗

arXiv2025

Experimental Demonstration of Efficient and Polarization-Diversity Fiber-Chip Coupling by 2D Grating Couplers with 193-nm DUV Lithography

Two-dimensional (2D) diffraction gratings offer a polarization-independent coupling solution between the planar photonic chips and optical fibers, with advantages including placement flexibility, ease of fabrication, and tolerance to alignment errors. In this work, we first proposed and experimentally demonstrated a highly efficient 2D grating coupler enabled by exciting multipolar resonances through bi-level dielectric structures. A 70-nm shallow-etched hole array and a 160-nm-thick deposited polycrystalline silicon tooth array are employed in our proposed 2D grating coupler. Strong optical field confinement and enhanced radiation directionality can thus be attained through the use of 193-nm deep-ultraviolet (DUV) lithography, which is readily accessible from commercial silicon photonics foundries. The measured experimental peak coupling efficiency is -2.54 dB with a minimum feature size of 180 nm. Our design exhibits a 3-dB bandwidth of around 23.4 nm with good positioning tolerance for optical fibers. Due to the benefits of perfectly vertical coupling, the measured polarization-dependent loss in our experiments is below 0.3 dB within the 3-dB working bandwidth. Our proposed 2D grating structure and design method can also be applied to other integrated optics platforms, enabling an efficient and polarization-diversity coupling between optical fibers and photonic chips while reducing requirements on feature size.

physics.optics↗

arXiv2025

Giant and Flexible Toroidal Circular Dichroism from Planar Chiral Metasurface

Chirality, a fundamental concept describing an object cannot superpose with its mirror image, is crucial in optics and photonics and leads to various exotic phenomena, such as circular dichroism, and optical activity. Recent findings reveal that, besides electric and magnetic dipoles, toroidal dipoles, an elusive part of dynamic multipoles, can also contribute significantly to chirality. However, as toroidal dipoles are typically represented by solenoidal currents circulating on a three-dimensional (3D) torus, toroidal circular dichroism is usually observed in 3D intricate microstructures. Facing corresponding challenges in fabrication, integration and application, it is generally difficult to employ toroidal circular dichroism in compact metasurfaces for flexible modulation of chiral interactions between electromagnetic waves and matter. To overcome these stringent challenges, we propose and experimentally demonstrate the giant toroidal circular dichroism in a bilayer metasurface that is comprised of only planar layers, effectively bypassing various restrictions imposed by 3D microstructures. With the introduction of a displacement, or bilayer offset, between the opposite layers, we experimentally achieve giant chiral responses with the intrinsic circular dichroism (CD) reaching 0.69 in measurements, and the CD can be quantitatively manipulated in a simple manner. The giant intrinsic chirality primarily originates from distinct excitations of in-plane toroidal dipole moments under circular polarized incidences, and the toroidal chiral response is quantitatively controlled by the bilayer offset. Therefore, our work provides a straightforward and versatile approach for development of giant and flexible intrinsic chirality through toroidal dipoles with inherently planar layers, important for applications in communications, sensing, and chiroptical devices.

physics.optics↗

arXiv2024

Programming on Bitcoin: A Survey of Layer 1 and Layer 2 Technologies in Bitcoin Ecosystem

This paper surveys innovative protocols that enhance the programming functionality of the Bitcoin blockchain, a key part of the "Bitcoin Ecosystem." Bitcoin utilizes the Unspent Transaction Output (UTXO) model and a stack-based script language for efficient peer-to-peer payments, but it faces limitations in programming capability and throughput. The 2021 Taproot upgrade introduced the Schnorr signature algorithm and P2TR transaction type, significantly improving Bitcoin's privacy and programming capabilities. This upgrade has led to the development of protocols like Ordinals, Atomicals, and BitVM, which enhance Bitcoin's programming functionality and enrich its ecosystem. We explore the technical aspects of the Taproot upgrade and examine Bitcoin Layer 1 protocols that leverage Taproot's features to program non-fungible tokens (NFTs) into transactions, including Ordinals and Atomicals, along with the fungible token standards BRC-20 and ARC-20. Additionally, we categorize certain Bitcoin ecosystem protocols as Layer 2 solutions similar to Ethereum's, analyzing their impact on Bitcoin's performance. By analyzing data from the Bitcoin blockchain, we gather metrics on block capacity, miner fees, and the growth of Taproot transactions. Our findings confirm the positive effects of these protocols on Bitcoin's mainnet, bridging gaps in the literature regarding Bitcoin's programming capabilities and ecosystem protocols and providing valuable insights for practitioners and researchers.

cs.CR↗