arXiv subjects

Jensen Li

Publications and source records attributed to Jensen Li.

At least 19 recordsLinked to original sources

arXiv2026

Real-space Hybrid Topological Singularities in Structured Elastic Waves

Real-space singularities govern a broad spectrum of wave phenomena, yet they remain largely unexplored in elastic wave systems. Here, we report hybrid topological singularities that emerge on the surfaces of finite-sized solids due to the full vectorial character of elastic waves. These textures fuse spin-field singularities with displacement-field singularities and exhibit unique non-pairwise topological charge dynamics. Moreover, a subset of these singularities imprint dislocation lines onto the radiated acoustic field, generating robust acoustic vortices in free space from an otherwise achiral source and structure. Our results establish elastic waves as a powerful platform for engineering real-space singularities and open avenues for singular phononics and the exploration of rich topological defects in elastic media.

physics.app-ph↗

arXiv2025

Path-Optimized Fast Quasi-Adiabatic Driving in Coupled Elastic Waveguides

Fast quasi-adiabatic driving (FAQUAD) is a central technique in shortcuts to adiabaticity (STA), enabling accelerated adiabatic evolution by optimizing the rate of change of a single control parameter. However, many realistic systems are governed by multiple coupled parameters, where the adiabatic condition depends not only on the local rate of change but also on the path through parameter space. Here, we introduce an enhanced FAQUAD framework that incorporates path optimization in addition to conventional velocity optimization, extending STA control to two-dimensional parameter spaces. We implement this concept in a coupled elastic-waveguide system, where the synthetic parameters-detuning and coupling-are controlled by the thicknesses of the waveguides and connecting bridges. Using scanning laser Doppler vibrometry, we directly map the flexural-wave field and observe adiabatic energy transfer along the optimized path in parameter space. This elastic-wave platform provides a versatile classical analogue for exploring multidimensional adiabatic control, demonstrating efficient and compact implementation of shortcut-to-adiabaticity protocols.

physics.app-ph↗

arXiv2025

Data-driven discovery of thermal illusions through latent-space geometry

Illusion effects-where one object appears as another-arise from the non-uniqueness of physical systems, in which different material configurations yield identical external responses. Conventional approaches, such as coordinate transformation, map equivalent configurations but provide only specific solutions, while analytical or numerical optimization methods extend these designs by minimizing scattering yet remain constrained by model assumptions and computational cost. Here, we exploit this non-uniqueness through a data-driven framework that uses a variational autoencoder to compress high-dimensional thermal-field data into a compact latent space capturing geometrical relations between configurations and observations. In this latent space, thermal illusion corresponds to finding configurations that minimize geometric distance to a target configuration, with thermal cloaking as a special case where the target is free space. Specifically, we demonstrate the concept in a cylindrical shell with anisotropic thermal conductivities enclosing a core of arbitrary conductivity, achieving robust thermal illusion and cloaking using only positive conductivities. Such a latent-space distance approach provides a refreshed perspective for achieving illusion and can be applied to inverse-design problems in other classical wave systems.

physics.app-ph↗

arXiv2025

Bell-State Quantum Holography with Metasurfaces

Metasurfaces composed of subwavelength nanostructures enable simultaneous control of polarization and wavefront, greatly enhancing holographic information capacity. Building on this capability, we extend holography into the quantum domain by experimentally realizing Bell-state holograms-distinct holographic images encoded in polarization-entangled Bell states of photon pairs. A polarization-multiplexed dielectric metasurface generates spatial modes conditioned on both input and output polarizations, entangling the holographic pattern with the two-photon state. To characterize these quantum holograms, we further develop quantum hologram tomography, reconstructing the full density matrix of the holographic state pixel by pixel. The reconstructed density-matrix hologram reveals tailor-made holographic symbols attached to individual Bell states through the metasurface, with contrast built up among the different Bell components as theory shows. This framework unifies metasurface photonics with quantum-state reconstruction and provides a scalable route toward high-dimensional quantum communication, encryption and information processing based on holographically encoded quantum light.

physics.optics↗

arXiv2025

Non-Markovian Exceptional Points by Interpolating Quantum Channels

Exceptional points (EPs) are special points in non-Hermitian systems where both eigenvalues and eigenvectors coalesce. In open quantum systems, these points are typically analyzed using effective non-Hermitian Hamiltonians or Liouvillian superoperators. While quantum channels offer the most general framework for describing state evolution in such systems, the existence and properties of EPs within this setting remain largely unexplored. In this work, we present a general strategy for generating quantum EPs for a single-qubit setting. We show that quantum channels can be separated into two distinct phases, with the transition between them marked by the presence of an EP. Based on this, we propose a systematic method to realize EPs by interpolating between quantum channels representing different phases. Experimentally, we implement these interpolated channels on a nuclear magnetic resonance (NMR) quantum computer and confirm the emergence of second-order EPs with high fidelity. Extending the interpolation to three channels further reveals third-order EPs. Our results establish quantum channel interpolation as a versatile framework for generating EPs and provide a general description of EPs in open quantum systems.

quant-ph↗

arXiv2025

Eigenmode-Guided Amplification via Spatiotemporal Active Acoustic Metamaterials

We present a spatiotemporal gain-loss framework for eigenmode steering in coupled acoustic resonators. A cross-coupled gain-loss coefficient links the gain of one resonator to the intensity of its partner, creating nonlinear feedback that conserves total energy while driving the system toward the eigenmode associated with the eigenvalue having the largest imaginary part-a deterministic eigenmode collapse. Spatial gain-loss profiles shape the eigenvalue spectrum and attractor landscape, while temporal modulation governs the transition dynamics. When symmetry prevents direct access to a target eigenmode, controlled spatiotemporal perturbations enable otherwise symmetry-forbidden transitions and accelerate convergence. Within this framework, parity-time (PT) symmetry appears as a special case, allowing tunable switching between collapse and Rabi-like oscillations near the exceptional point. Full-wave simulations of coupled Helmholtz resonators confirm precise and programmable acoustic energy routing, establishing spatiotemporal gain-loss engineering as a route to reconfigurable wave control and analog information processing.

physics.app-ph↗

arXiv2025

Searching for topological semi-complete bandgap in elastic truss lattices

Gapless topological phases have attracted significant interest across both quantum and classical systems owing to their novel physics and promising applications. However, the search for ideal gapless topological nodes inside a clear bandgap is still lacking in elastic systems. The degenerate points are always hidden in the trivial bulk bands due to the intricate elastic modes involved. Here, we find a topological semi-complete bandgap in a three-dimensional elastic truss lattice by tuning a supporting rod, which exhibits a complete bandgap except for the inevitable topological degenerate points. Furthermore, we experimentally map the topological semi-complete bandgap and the inside nontrivial surface state arcs with a scanning laser vibrometer. The introduced scheme provides a systematic approach for the idealization of semi-complete bandgaps and thus may significantly advance the practical utility of topological phases in mechanical engineering domains.

cond-mat.mes-hall↗

arXiv2025

Temporal Effective Medium for Programmable Acoustic Metamaterials with Multiple Resonances

We extend effective medium theory (EMT) to time-modulated, frequency-dispersive acoustic metamaterials with multiple resonances. While previous studies focused on non-dispersive or single-resonance systems, advances in programmable materials now enable precise control of time-varying responses. We derive explicit averaging rules that account for the interplay between resonant and modulation frequencies. When resonant frequencies are much lower than the modulation frequency, modulating the resonant strength yields the temporal average of monopolar susceptibility \c{hi}, while modulating the resonant frequency results in the average of 1/\c{hi}, applied per resonance mode. In hybrid cases, high-frequency resonances (relative to modulation) can be renormalized as a non-dispersive background before averaging the rest. This generalized temporal EMT offers a unified framework for designing compact, topologically robust, and non-Hermitian acoustic devices, leveraging the possible programmability of time-dependent material parameters in future.

physics.app-ph↗

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 2{\pi} 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 2{\pi} 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 2{\pi} 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

Metalens array for complex-valued optical discrete Fourier transform

Photonic computing has emerged as a promising platform for accelerating computational tasks with high degrees of parallelism, such as image processing and neural network. We present meta-DFT (discrete Fourier transform), a single layer metasurface device, designed to perform optical complex-to-complex DFT with O(N) time complexity. One critical challenge in free-space analog optical computing is to control the measurement error. Our scheme addresses this issue by focusing light on spatially separated focal points and reconstructing the complex phase, which enable error correction. We systematically evaluate the device's performance using input vectors with random complex amplitudes and phases, to demonstrate its robust accuracy. Our findings pave the way towards advancement of metasurface-based computation, offering a robust framework that is readily extensible to an arbitrary complex-valued matrix-vector multiplication (MVM).

physics.optics↗

arXiv2025

Metamaterial sound absorbers based on microperforated panels: an approach toward enhanced flexibility and near-limit broadband performance

Traditional microperforated panels (MPPs) and metamaterial-based sound absorbers rely on local resonances or multi-resonator designs, which limit their bandwidth, angular applicability, and ease of fabrication. Leveraging the reciprocity theorem and cavity resonances, we introduce a new class of robust MPP absorbers, termed meta-MPPs, capable of achieving ultrabroadband near-total sound absorption across a range of 0.37 to 10 kHz. These absorbers demonstrate average performance exceeding that of traditional MPPs by over 100%, approaching the theoretical causality limit. Notably, their absorption performance can be tuned between angularly asymmetric and omnidirectional modes and remains highly robust to variations in MPP parameters and geometrical configurations. Validated through simulations and experiments, our findings present a simpler, more robust, and highly adaptable solution for noise control.

physics.app-ph↗

arXiv2024

Programmable lattices for non-Abelian topological photonics and braiding

Non-Abelian physics, originating from noncommutative sequences of operations, unveils novel topological degrees of freedom for advancing band theory and quantum computation. In photonics, significant efforts have been devoted to developing reconfigurable non-Abelian platforms, serving both as classical testbeds for non-Abelian quantum phenomena and as programmable systems that harness topological complexities. Here we establish topological spinor lattices for non-Abelian programmable photonics. We design a building block for reconfigurable unitary coupling between pseudospin resonances, achieving a universal set of rotation gates through coupling along the unit cell boundary. The lattice assembly of our building blocks enables the emulation of the extended quantum Hall family across various eigenspinor bases. Particularly, we reveal the emergence of a non-Abelian interface even when the bulks are Abelian, which allows the topologically trivial engineering of topologically protected edge states. We also define the braid group for pseudospin observables, demonstrating non-Abelian braiding operations and the Yang-Baxter relations. Our results pave the way for realizing a reconfigurable testbed for a wide class of Abelian and non-Abelian topological phenomena and braiding operations.

physics.optics↗

arXiv2024

Nonreciprocal Local-Resonance Induced Complex Band Hybridization

We study the complex band hybridization induced by nonreciprocal local resonances in photonic crystals. Composed of trimer unit cells, a two-dimensional (2D) magnetophotonic crystal with an analytically obtainable solution is considered. We find that nonreciprocal spectral gap may appear without nonreciprocal transmission and that the imaginary parts of the complex wavevectors $\text{Im}(\mathbf{k})$ may blow up at resonance to give extreme nonreciprocal transmission. We further show that, for a subwavelegnth lattice, the isolation ratio for the nonreciprocal transmission is determined solely by $\text{Im}(\mathbf{k})$ instead of the extensively studied real part $\text{Re}(\mathbf{k})$. Our finding contradicts the common belief that "spectral nonreciprocity [$\omega(\mathbf{k})\neq\omega(-\mathbf{k})$] always implies nonreciprocal transmission".

physics.optics↗

arXiv2024

Metasurface-enabled quantum holograms with hybrid entanglement

Metasurfaces, with their capability to control all possible dimensions of light, have become integral to quantum optical applications, including quantum state generation, operation, and tomography. In this work, we utilize a metasurface to generate polarization-hologram hybrid entanglement between a signal-idler photon pair to construct a quantum hologram. The properties of the quantum hologram can be revealed by collapsing the polarization degree of freedom of the idler photon, inducing interference between two holographic states of the signal photon, as a meaningful and selective erasure of the holographic content. In contrary, interference disappears when the idler photon is detected without observing polarization. This process can be further interpreted as a quantum holographic eraser, where the erasing action is visualized with erased contents in holograms. Our construction of polarization-hologram hybrid entangled state with metasurfaces will be useful for quantum communication with enhanced robustness, anti-counterfeiting applications through the additional quantum degrees of freedom, and as an emerging platform for exploring fundamental quantum concepts for entanglement and non-locality.

quant-ph↗

arXiv2024

Frequency-selective terahertz wave amplification by a time-boundary-engineered Huygens metasurface

Ultrafast manipulation of optical resonance can establish the time-boundary effect in time-variant media leading to a new degree of freedom for coherent control of electromagnetic waves. Here, we demonstrate that a free-standing all dielectric Huygens metasurface of degenerate electric and magnetic resonances can prompt the broadband near-unity transmission in its static state, whereas it enables wave amplification in the presence of time boundary. The time boundary is realized by femtosecond laser excitations that transiently inject free carriers into the constituent meta-atoms for dynamic removal of a pre-established two-fold degeneracy. We observe that the transmittance in the photo-excited Huygens metasurface can exceed unity transmittance, i.e., THz wave amplification, by a factor over 20% in intensity at frequencies tunable by varying the arrival of time boundary with respect to that of the seed terahertz pulse. By numerical simulations and analysis with time-dependent coupled mode theory, we show that the wave amplification results from the ultrafast Q-switching and shift in resonant frequencies. This work demonstrates a new approach to achieve tunable amplification in an optical microcavity by exploiting the concept of time-variant media and the unique electromagnetic properties of Huygens metasurface.

physics.optics↗

arXiv2024

Complete Interband Transitions for Non-Hermitian Spin-Orbit-Coupled Cold-Atom Systems

Recently, synthetic spin-orbit coupling has been introduced into cold-atom systems for more flexible control of the Hamiltonian, which was further made time-varying through two-photon detuning to achieve dynamic control of the cold-atom state. While an intraband transition can be adiabatically obtained, a complete interband transition, rather than a superposition of different bands, obtained through fast sweeping is usually guaranteed by having the positions of the initial and final states be far away from any band gap in the quasimomentum space. Here, by introducing an additional non-Hermitian parameter through an atom-loss contrast together with two-photon detuning as two controllable external parameters, both intraband and complete interband transitions can be achieved independent of the positions of the initial and final states. In addition, a point-source diagram approach in the 2D external parameter space is developed to visualize and predict the locations of any nonadiabatic transitions. This control protocol can have potential applications in quantum state control and quantum simulations using cold-atom systems.

quant-ph↗

arXiv2023

Flexural wave illusion on a curved plate

Manipulating elastic waves using a transformation approach is challenging due to the complex constitutive relationship. However, for flexural waves, approximated as scalar waves, two straightforward approaches emerge based on geometric curvature and plate thickness. Here, we develop transformation theory to establish equivalence between curved plates of different shapes and thickness profiles. By introducing tailor-made thickness profiles on a given curved shape enables illusion effects, where flexural waves propagate as if on a flat plate or on another curved plate with totally different configuration. Numerical simulations and experimental field mapping confirm the effectiveness of these illusions. Our approach on flexural wave illusion finds applications in structural designs with material and shape constraints, and holds potential for vibration control, wavefront shaping, chaotic dynamics and topology control.

physics.app-ph↗

arXiv2023

Experiment-based deep learning approach for power allocation with a programmable metasurface

Deep learning, as a highly efficient method for metasurface inverse design, commonly use simulation data to train deep neural networks (DNNs) that can map desired functionalities to proper metasurface designs. However, the assumptions and simplifications made in the simulation model may not reflect the actual behavior of a complex system, leading to suboptimal performance of the DNNs in practical scenarios. To address this issue, we propose an experiment-based deep learning approach for metasurface inverse design and demonstrate its effectiveness for power allocation in complex environments with obstacles. Enabled by the tunability of a programmable metasurface, large sets of experimental data in various configurations can be collected for DNN training. The DNN trained by experimental data can inherently incorporate complex factors and can adapt to changed environments through its on-site data-collecting and fast-retraining capability. The proposed experiment-based DNN holds the potential for intelligent and energy-efficient wireless communication in complex indoor environments.

eess.SP↗