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Wednesday 9 September

Applied Physics

Spectral Geometry and Dispersion-Constrained Projection of Diffusive Fields

Pengfei Zhu, Julien Lecompagnon, Philipp Daniel Hirsch et al. (+1 more)

Diffusive fields obey operator-imposed relations between spatial structure and temporal decay, yet conventional spectral filtering selects components primarily according to frequency or wavenumber magnitude. Here we show that the diffusion operator defines a spectral geometry in the joint space of spatial wavenumber and modal decay rate, where physically admissible modes occupy the manifold $\eta=\alpha|\mathbf{k}|^2$. This geometry separates spectral scale from physical consistency: high-wavenumber modes can remain diffusion-consistent, whereas lower-wavenumber modes can violate the governing dynamics. We exploit this distinction by introducing an operator residual and a finite-width soft projection that selects spectral components according to their distance from the diffusion manifold rather than their spectral magnitude. Numerical studies demonstrate robust recovery under noise, diffusivity mismatch, and finite acquisition, and reveal a consistency–retention tradeoff governed by the manifold width. Photothermal experiments further confirm that the projection suppresses off-manifold spectral content while retaining the dominant thermal response. These results establish operator consistency as a spectral-selection principle for diffusive fields and provide a geometric framework for physics-informed processing of dissipative systems.
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All authors Pengfei Zhu, Julien Lecompagnon, Philipp Daniel Hirsch, Mathias Ziegler

Applied Physics

Through-thickness coupling of diffusion and viscoelastic relaxation in the transient bending of bilayer microcantilevers

YingCheng Zhou, Kosuke Minami and Genki Yoshikawa

Static-mode microcantilever sensors detect chemical analytes through the bending of a bilayer beam whose polymer coating swells upon absorption. The transient bending is usually modeled as if the coating absorbed analyte uniformly, which is adequate for thin coatings but breaks down as the coating thickens and a moving diffusion front couples to depth-dependent viscoelastic relaxation. We resolve this coupling with a purpose-built finite-element solver requiring only one linear solve per time step, and show that the through-thickness structure controls the transient response in ways uniform-uptake models cannot capture. Verified against a published analytical solution, the solver reproduces the full transition from a pronounced curvature overshoot (up to nearly twice the steady-state value) when diffusion is fast relative to relaxation to a monotonic rise when it is slow. In the intermediate-thickness regime the analytical solution cannot reach, the thickness maximizing the steady-state signal and the thickness preserving the transient overshoot are governed by different physics, one geometric and one dynamic, so one coating cannot be optimized for both. The overshoot further survives realistic surface mass-transfer resistance, justifying the idealized surface boundary condition used throughout.
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Applied Physics

Maximum signal-to-noise ratio enhancement by averaging under a limited measurement time

YingCheng Zhou, Kosuke Minami, Genki Yoshikawa et al. (+1 more)

Averaging through repetitive measurement is a ubiquitous strategy for improving signal-to-noise ratio (SNR) and is commonly assumed to yield a $\sqrt{N}$ enhancement with the number of repetitions $N$. This assumption, however, implicitly requires the signal amplitude to be independent of measurement duration. This condition does not generally hold in dynamical sensing systems with finite response time and a fixed measurement time. We derive a closed-form expression for the SNR enhancement factor by analytically accounting for the competition between statistical noise reduction and dynamical signal attenuation, and demonstrate the existence of a strict upper bound on the SNR enhancement. The enhancement factor is a non-monotonic function of $N$ with a well-defined maximum at an optimal repetition number, beyond which further averaging degrades the SNR. Moreover, below a threshold set by the ratio of measurement time to response time, averaging yields no enhancement at all. These two regimes delimit where the conventional $\sqrt{N}$ law breaks down. Experimental validation using nanomechanical gas sensing, with two receptor-analyte systems deliberately chosen to bracket this enhancement transition, confirms the theoretical predictions. Our results show that measurement time is a finite resource to be optimally partitioned between signal accumulation and averaging, and provide a quantitative guideline for selecting the repetition number in time-constrained sensing such as real-time and repetitive gas or odor detection.
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All authors YingCheng Zhou, Kosuke Minami, Genki Yoshikawa, Gaku Imamura

Applied Physics

A Predictive Design Framework for a Soft Robotic Ventricle using Contractile Actuators

Jeongmin Kim, Qiong Wang, Liuyang Cheng et al. (+4 more)

The natural cardiac cycle is divided into the systole and diastole phases which encompass four distinct stages: isovolumetric contraction and ejection during systole, followed by isovolumetric relaxation and filling during diastole. Cardiovascular modeling of this cycle ranges from high-fidelity multiphysics simulations to reduced-order lumped-parameter (Windkessel) representation of the heart-artery coupling. However, current models do not relate the mechanics of the actuator driving the ventricle pump to the hemodynamics. In this study, we develop and experimentally validate a predictive design framework for ventricle-like pumps using various types of soft contractile actuators. We build a circulatory loop which reproduces the entire loop including the isovolumetric phases-where pressure changes occur without volume shifts. The framework is based on a lumped-parameter model, hereafter referred to as the phase-dependent Actuator-driven Windkessel 3-element (AWK3) model, to bridge soft actuator mechanics to the cardiac pressure-volume (P-V) loop. Unlike traditional models that require either pressure or volume as a fixed input to estimate the other, our proposed model predicts both variables when informed by the isometric characteristics of the actuators. We validate the model using a ventricle-inspired pump driven by a linear contractile series-elastic actuator or twisted and coiled polymer actuators (TCPA). We relate the actuator isometric testing protocol to the phase-dependent AWK3 model, which replicates the Frank-Starling law, accurately describing cardiac behavior under varying conditions of preload, afterload, and inotropy (contractility). This approach provides a robust platform for the design and high-fidelity control of bio-inspired soft robotic circulatory systems.
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All authors Jeongmin Kim, Qiong Wang, Liuyang Cheng, Samuel Tsai, Seong Hyeon Kim, Harma K. Turbendian, Sameh Tawfick

Applied Physics

Round-the-Clock Sub-Ambient Cooling via Dynamic Sky View Factor Steering

Qiuyu Chen, Minghao Dong, Zheng Zhang et al. (+3 more)

Passive daytime radiative cooling holds significant potential to address sustainability challenges such as the energy-water nexus. However, common static horizontal configurations cannot respond to dynamic changes of environmental conditions such as solar position and cloud coverage, thereby forfeiting the opportunity of optimizing the cooling performance in the 24-h day-night cycle. Here, inspired from the heliotropism of sunflowers, we develop a dynamic sky view factor steering (DSVFS) system. By dynamically steering the emitter to an optimal angle, this system not only relaxes the stringent dual requirement of ultra-high solar reflectivity and infrared emissivity of the radiative emitter, but also maximizes its cooling power round-the clock. Using this DSVFS system, we experimentally demonstrate sub-ambient cooling during a typical hot noon even with a near-blackbody emitter; with a selective emitter, we demonstrate an increase of cooling power by 135% as compared to its static counterpart. Case studies of multiple cities across the world indicate a maximum annual electricity saving of up to 200 kWh/m^2.
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All authors Qiuyu Chen, Minghao Dong, Zheng Zhang, Xiaodonog Zhao, Peng Xiao, Zhen Chen

Applied Physics · Cross-listed from cond-mat.mtrl-sci

Heteroepitaxial Growth of PbSe on InP Substrates via Lattice-Matched III-V Buffer Layers

Biridiana Rodriguez, Mark Martino, Brody Yeung et al. (+2 more)

Detector cost remains a barrier to the widespread adoption of mid-wave infrared (3-5 micron) technology. PbSe, an inexpensive narrow band gap IV-VI semiconductor that has been used since the early 1940s, delivers high performance for infrared detection despite the abundance of grain boundaries in polycrystalline films. Epitaxial growth, however, could provide superior crystalline quality and interfaces, but suitable substrates remain limited for PbSe. Recent PbSe heteroepitaxy has focused primarily on III-V, II-VI and group-IV substrates that each offer a comparatively narrow range of lattice-matched alloys for heterostructure engineering. Here we show that InP-based heteroepitaxy provides access to a broader materials platform while limiting the lattice mismatch with PbSe to approximately 4%. We grow 150-nm thick PbSe films by molecular beam epitaxy on 200-nm thick In0.53Ga0.47As and In0.52Al0.48As buffers on (001) InP substrates. Reflection high-energy electron diffraction and X-ray diffraction show (001)-oriented rock-salt PbSe with an out-of-plane lattice constant of 6.12 Angstrom on both buffers. Photoluminescence (PL) is observed from room-temperature down to 12 K and the peak wavelength red-shifts from 3.7 to 5.0 microns. Under identical measurement conditions, the room-temperature peak PL intensities from films on In0.53Ga0.47As and In0.52Al0.48As are approximately 1.9x and 1.3x that of a PbSe on GaAs substrate reference, respectively. These results establish an InP-compatible platform for integrating narrow band-gap PbSe with a broad range of ternary and quaternary III-V alloys, including, for example, structures in which In0.53Ga0.47As serves as both a short-wave infrared absorber and a template for PbSe growth.
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All authors Biridiana Rodriguez, Mark Martino, Brody Yeung, Benjamin Sprenger, Leland Nordin

Tuesday 8 September

Applied Physics

Dynamic Sensing via Photomodulated Gas Desorption in Plasmonic Nanoparticle Chemiresistors

Lukas Mielke, Dahee Heo, Gabriele Carelli et al. (+1 more)

Quasi-static sensing, i.e., measurement of a sensor signal change induced by analyte presence with respect to a baseline signal observed in a reference gas beforehand, is the state of the art for qualitative and quantitative analyte identification in chemiresistive sensing. However, this approach is prone to baseline drift and, especially for inexpensive miniaturized point-of-care sensors, repeated calibration with reference gas is not feasible. To access reliable baseline information, active switching between analyte and reference gas would be required, causing a limitation for miniaturized implementation. Dynamic excitation of sensors offers an alternative: Via external stimuli the sensor is reversibly driven out of equilibrium in a controlled way, and the resulting transient sensor response, which is dependent on analytes present, is recorded and interpreted. Correlation of excitation and response signals can reduce effects of baseline drift and furthermore, dynamic features in sensor responses may contain valuable information. Especially light activation is a powerful and potentially miniaturizable approach to agitate sorption processes and therefore induce dynamics. In this work we report photothermal heating of hybrid, chemiresistive gold nanoparticle composites via LED excitation matching the plasmon resonance, to dynamically shift the analyte sorption equilibrium and induce dynamic sensor responses in a highly controlled way. We demonstrate that these sensor responses enable the detection of volatile organic compounds (VOC) via interpretation of differential signal components and that this approach improves the chemiresistors' baseline stability.
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All authors Lukas Mielke, Dahee Heo, Gabriele Carelli, Hendrik Schlicke

Applied Physics · Cross-listed from physics.optics

Encoding Propagation Invariance into Light

Wenxiang Yan, Tianyue Li, Zhuolin Wu et al. (+6 more)

Diffraction governs the axial evolution of optical fields, whereas conventional holographic synthesis primarily controls their transverse structure. Here we add axial diffraction management as an additional design freedom to the transverse_field programmability of holography, enabling the transverse optical function and its diffraction-driven axial evolution to be co_designed. By incorporating established propagation_invariant dynamics into computer_generated hologram and meta_hologram synthesis, we realize task_selectable axial responses in user_defined monochromatic, full-colour and vectorial fields. On a spatial light modulator, the same scalar user_defined field is configured either for a rapidly evolving 1.2_cm depth of field or for an approximately 75_cm propagation_invariant range. Millimetre_scale metasurfaces further enable metre_scale refocusing_free full_colour projection and vectorial colour fields with polarization textures preserved over more than 30 cm. This transverse_axial co_design framework extends holographic field synthesis beyond transverse programmability, providing a broadly compatible route towards task_configurable optical systems and compact multidimensional photonics.
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All authors Wenxiang Yan, Tianyue Li, Zhuolin Wu, Yiyu Zhao, Zhi-Cheng Ren, Xi-Lin Wang, Hui-Tian Wang, Shuming Wang, Jianping Ding

Applied Physics · Cross-listed from physics.optics

Magic-free coexisting photonic and phononic moiré flat bands

Ziming Chen, Kaiyu Cui, Ning Wu et al. (+8 more)

Moiré flat bands enhance localization and interactions through suppressed group velocity, but existing approaches largely target a single physical field because distinct excitations generally require different, finely tuned magic configurations. Here we introduce a flat-band mechanism based on strong diffractive hybridization among moiré-folded bands. Period-mismatched modulations open distinct coupling channels whose hybridization renormalizes the band dispersion. An effective Hamiltonian shows that increasing the diffractive coupling progressively suppresses the group velocity, driving the system toward a flat-band regime without field-specific magic configurations. This coupling-induced mechanism enables band flattening across distinct physical excitations. We demonstrate this mechanism in a single-layer moiré optomechanical crystal, where photonic and phononic flat bands are simultaneously realized, and their localized modes and optomechanical interaction are experimentally observed. Beyond photonic and phononic systems, this mechanism may extend to other wave and quasiparticle platforms, providing a general route to co-localizing and coupling distinct physical fields in moiré systems.
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All authors Ziming Chen, Kaiyu Cui, Ning Wu, Shuyuan Li, Chenxuan Wang, Xue Feng, Fang Liu, Wei Zhang, Hao Sun, Yongzhuo Li, Yidong Huang

Applied Physics · Cross-listed from quant-ph

Instantaneous-Frame Theory of Strongly Driven Parametric Gates

Kentaro Kubo, Shinichi Inoue, Jushin Tei et al. (+3 more)

Parametric two-qubit gates using tunable couplers are a promising approach to scalable superconducting quantum processors. However, conventional theories formulated in the idle eigenbasis break down in the large-amplitude regime required for fast gate operations. Here, we show that parametric gates are more naturally and accurately described as coherent rotations between instantaneous eigenstates rather than idle eigenstates. This approach may appear counterintuitive, since instantaneous eigenbases are usually associated with adiabatic dynamics. However, they also form a natural moving frame for driven dynamics, where the non-Abelian Berry connection governs transitions and provides a compact description of the exchange and effective $ZZ$ couplings. We show that this theory achieves quantitative agreement with exact numerical simulations across representative tunable-coupler architectures, including double-transmon, capacitively shunted double-transmon, and single-transmon couplers. The description remains accurate even in regimes where idle-frame descriptions fail, while substantially reducing the reliance on computationally demanding exact simulations. These results establish an instantaneous-frame theory of parametric gates beyond conventional idle-frame models and provide a new perspective on driven quantum dynamics.
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All authors Kentaro Kubo, Shinichi Inoue, Jushin Tei, Yinghao Ho, Yasunobu Nakamura, Hayato Goto

Monday 7 September

Applied Physics

Capacitance of Undoped Thin-Film Diodes

Oskar J. Sandberg, Mathias Nyman, Stefan Zeiske et al. (+3 more)

The capacitance of thin-film diodes based on undoped semiconductors are dominated by injected charge carriers rather than doping-induced carriers. However, an analytical framework of the capacitance in these devices has remained elusive. Here, we derive an analytical description of the capacitance, fully accounting for injected charge carrier and electrode charge effects. Based on these findings, a method to extract the built-in voltage in these devices is presented. The theoretical framework is substantiated numerically by drift-diffusion simulations and experimentally on organic solar cells.
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All authors Oskar J. Sandberg, Mathias Nyman, Stefan Zeiske, Staffan Dahlstrom, Johannes Benduhn, Ardalan Armin

Applied Physics

Wave-based reading of mechanical memory in multistable mass-in-mass metamaterials

Audrey Watkins, Giovanni Bordiga, Vincent Tournat et al. (+1 more)

Mechanical metamaterials with integrated bistable elements have emerged as promising platforms for mechanical information storage, where transitions between stable states encode information as mechanical bits. While it has been shown that information can be written into such metamaterials by applying global inputs, existing readout strategies rely predominantly on visual inspection. Here, we experimentally demonstrate a mass-in-mass bistable metamaterial with state-dependent stiffness that enables both writing and reading of mechanical information using only boundary-applied dynamic excitations. We further show that such metamaterial architecture functions as both a mechanical sensor of input amplitude and a reconfigurable wave-control device. Together, these results highlight the versatility of bistable metamaterials as multifunctional platforms that integrate mechanical memory, sensing, and adaptive wave manipulation.
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All authors Audrey Watkins, Giovanni Bordiga, Vincent Tournat, Katia Bertoldi

Applied Physics · Cross-listed from cond-mat.mtrl-sci

High-Field Electron Transport in AlGaN alloys: A Full-Band Monte Carlo Study Based on Ab Initio Supercell Calculations

Animesh Datta, Matinehsadat Hosseinigheidari and Uttam Singisetti

AlGaN alloys are promising wide and ultra-wide-bandgap semiconductors for next-generation power and RF electronics applications. To realize the full potential of AlGaN based devices, it is important to understand the electron transport to accurately predict device performance and identify material limits under various operating conditions. In this work, the high-field electron transport properties of AlxGa1-xN are investigated using a supercell based full band Monte Carlo method. The supercell approach is employed to explicitly capture the true disorder of the alloy system, enabling a more realistic description of carrier transport. The velocity field characteristics are calculated across a range of Al compositions to evaluate key transport metrics, including peak velocity, saturation velocity, and critical electric field. The role of different scattering mechanisms is studied in detail to understand the high field transport mechanism in the AlGaN alloy system. In addition to steady state transport, transient electron dynamics are examined for various Al fractions to study velocity-overshoot behavior, which is especially important for improving the performance of scaled RF devices. Finally, the temperature dependence of the velocity field characteristics in ultra-wide-bandgap Al0.75Ga0.25N is investigated to assess its transport performance under high temperature conditions. These results provide a detailed understanding of high-field transport in AlGaN alloys and offer guidance for the design of AlGaN-based RF and power electronic devices.
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Applied Physics

Quantum Sensing for Spatial Spin Noise Mapping via Nitrogen-Vacancy Magnetic Quenching in Diamond

Ashley J. Tyler, Thomas D. Bateman-Price, Bradley T. Flinn et al. (+4 more)

Detecting and mapping spin noise can reveal spatial variations in surface defect states, catalytic residues, free radicals, and spintronic materials. However, bulk measurements average over spatial heterogeneity, while scanning-probe maps require sequential rastering. Here, we demonstrate a microwave-free magnetic quenching (MQ) method for wide-field spin-noise mapping using nitrogen-vacancy (NV) centres in diamond. The protocol combines continuous LED illumination with a low-frequency, amplitude-modulated magnetic field, avoiding resonant microwave delivery or pulsed optical hardware. Field-induced spin-state mixing reduces NV photoluminescence, providing the primary contrast mechanism. We examine the response as a function of optical power and magnetic modulation amplitude, interpreting the results using a spin-state mixing model. The method is validated with aqueous gadobutrol concentration series, showing trends consistent with optically detected magnetic resonance (ODMR) measurements. We map spin-noise variations across boron nitride and single-walled carbon nanotube samples with differing defect and metallic catalyst contributions, supported by electron microscopy and spectroscopy. Notably, MQ detects a spin-noise response in boron nitride nanotubes that is silent in bulk EPR spectroscopy. This approach provides a practical framework for spatially resolved spin-noise sensing across quantum technologies and advanced functional materials.
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All authors Ashley J. Tyler, Thomas D. Bateman-Price, Bradley T. Flinn, William J. Cull, Tom J. P. Irons, Andrei N. Khlobystov, Melissa L. Mather

Applied Physics · Cross-listed from eess.SY

Noninvasive Anisotropic Identification of Magnetic Properties in Toroidal Shaped Magnetic Steel

Xusen Qin, Reza Zeinali and Mitrofan Curti

This research proposes a model-free inverse approach for identifying the nonlinear anisotropic single-valued magnetic constitutive characteristics of soft magnetic materials from boundary measurements. Using the harmonic approximation, the internal magnetic flux density B and magnetic field strength H are independently reconstructed from the measured boundary data, thus avoiding the limitation of using a predefined parametric B–H mapping function. Subsequently, the reconstructed fields are spatially averaged along selected collection lines to recover the B–H characteristics of the principal directions. Numerical results demonstrate high reconstruction accuracy for unperturbed data and good robustness against Gaussian perturbations of the boundary measurements, with the overall mean error remaining below 5% for a 10% noise level. These results indicate that under the harmonic-field assumptions, the field-based reconstruction provides a simple and computationally efficient framework for non-invasive identification of nonlinear anisotropic magnetic constitutive characteristics.
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Applied Physics · Cross-listed from physics.optics

Mechanical quality factor estimation from a nonlinear optical cavity response

Zohran Ali, Davide Tomasella, Daniel Allepuz Requena et al. (+2 more)

Intrinsic damping rate and quality factor ($Q$) are key parameters in optomechanical systems. However, in high-Q devices, their measurement is often challenging because probe-induced dynamical backaction (DBA) and the need to resolve and accurately track the mechanical resonance limit the performance of state-of-the-art techniques. Here, we introduce an all-optical ringdown method in the unresolved-sideband regime that exploits the nonlinear, time-averaged optical response induced by strong mechanical motion. We derive an analytical model of the time-averaged optical cavity response probed by a weak frequency-scanning laser. During the evolution of the mechanical oscillator, the excited motion modulates the Lorentzian lineshape into a double-horned profile whose peak separation enables an accurate estimation of the modulation amplitude. Tracking this response during the mechanical ringdown allows the intrinsic damping rate to be determined without resolving the mechanical oscillation. We apply the method to a density-modulated phononic crystal membrane placed inside a high-finesse cavity and obtain mechanical quality factors consistent with independent measurements on the same platform. Our method requires a minimal optical setup, while offering an in situ diagnostic and reduced impact from probe-induced DBA and robustness against measurement noise. Finally, the model can describe other resonant systems dispersively coupled to coherent frequency modulations, providing new insights and measurement strategies that expand beyond the optomechanical platform.
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All authors Zohran Ali, Davide Tomasella, Daniel Allepuz Requena, Alexander Huck, Ulrik Lund Andersen

Applied Physics

Dynamic distortion from discretized coupling feedback in soft-spin Ising machines

Victor H. González and Natalia G. Berloff

Although Ising machines (IMs) have grown in popularity due to their potential as physics-based accelerators for combinatorial optimization problems (COPs), most literature focuses on empirically-obtained benchmarks with low universality. In this work, we propose dynamic feedback distortion as a universal metric to quantify the effect of coupling field discretization in time-multiplexed IMs. Starting from the transfer functions of realistic hardware, we analytically show how this distortion can be mitigated using a global bias (or choosing the correct discrete coupling element) and injecting coloured noise. Our numerical results show that our mitigation protocols are very effective, especially in complicated energy landscapes (namely tunable Möbius ladders and 2D tiling problems); where an analogue reduction of the distortion leads to a two–three order of magnitude increase in the success rate of complex COPs.
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Applied Physics

An integrated viscoelastic modeling framework combining analytical and FEM approaches: Application to WSe2 coatings

Mohamed Bensalem, Fateh Bahadur, Yue Wang et al. (+2 more)

This work presents an integrated methodology combining analytical and finite element FEM based viscoelastic modeling for characterizing the nanoindentation response of coatings. The proposed framework combines two complementary modeling approaches: an analytical model based on the Burgers formulation to analyze nanoindentation load displacement data and extract rheological parameters, and a numerical FEM model implemented in ABAQUS using a 2D axisymmetric indenter coating substrate configuration with viscoelasticity represented through Prony series. An automated inverse optimization routine employing the Nelder Mead simplex algorithm minimizes the discrepancy between experimental and simulated responses. The methodology is demonstrated and validated on WSe2 coatings, showing an agreement between the analytical predictions, FEM simulations, and experimental measurements. Despite the geometric simplifications, the FEM approach provides accurate predictions while maintaining high computational efficiency of time dependent mechanical behavior. The proposed framework provides a robust tool for characterizing viscoelastic behavior from nanoindentation data while enabling access to internal stress and strain fields, thereby offering deeper insight into plastic deformation, crack initiation, and failure mechanism.
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All authors Mohamed Bensalem, Fateh Bahadur, Yue Wang, Nabil Daghbouj, Tomas Polcar

Applied Physics · Cross-listed from physics.atom-ph

Magnetic characterization of electronic components for portable atomic sensors using a zero-field optically pumped magnetometry platform

Hyeonjae Kim, Sangkyung Lee, Sin Hyuk Yim et al. (+2 more)

We present a zero-field optically pumped magnetometry platform for magnetic characterization of a photodetector (PD) board and a resistance temperature detector (RTD) used in a portable atomic magnetometer. For each component, the static magnetic field along the measurement axis is determined from the shift in the center of the dispersive response, while response distortion caused by off-axis magnetic-field components is assessed from the absorptive admixture. Magnetic-field noise is evaluated based on the quadrature difference in the amplitude spectral density (ASD). The platform achieved a -3 dB bandwidth of 71.5 Hz and a median ASD of 57.6 $\mathrm{fT}/\sqrt{\mathrm{Hz}}$ over 20-70 Hz. For the unpowered PD board, static magnetic fields of approximately 8 nT in magnitude and opposite signs were measured in the front- and back-facing orientations. The back-facing orientation also exhibited a degraded dispersive response consistent with magnetic-field inhomogeneity. The magnetic-noise contributions associated with the PD board were estimated at 36.0 and 63.2 $\mathrm{fT}/\sqrt{\mathrm{Hz}}$ in the front- and back-facing orientations, respectively. By contrast, operation of the RTD readout generated a static magnetic field of -0.6 nT, with no measurable response degradation or additional magnetic-field noise. These results provide guidance for the design and placement of electronic components in portable atomic magnetometers targeting sensitivities below 0.1 $\mathrm{pT}/\sqrt{\mathrm{Hz}}$.
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All authors Hyeonjae Kim, Sangkyung Lee, Sin Hyuk Yim, Taek Jeong, Younghoon Lim

Applied Physics · Cross-listed from quant-ph

Qubit-Based Benchmarking of InP HEMT LNAs: Readout Fidelity Versus Power Consumption

Junjie Li

High-fidelity single-shot readout of superconducting qubits is essential for fault-tolerant quantum computation. Without a quantum-limited amplifier such as a Josephson parametric amplifier, the cryogenic high-electron-mobility-transistor (HEMT) low-noise amplifier (LNA) at the 4 K stage is the dominant noise source in the readout chain. HEMT LNAs are conventionally characterized by Y-factor measurements of the noise temperature $T_N$, independently of the quantum measurement they ultimately serve. Here we present a qubit-in-the-loop benchmarking method. The method uses the two-dimensional IQ histogram of single-shot readout as a direct figure of merit. We apply it to three state-of-the-art cryogenic InP HEMT LNAs with 53%, 60%, and 70% channel indium content, together with a commercial reference amplifier. The 60% and 70% devices have similar $T_N$ in Y-factor measurements, both lower than the 53% device. The 70% device has the highest gain, but qubit readout SNR and assignment fidelity $\mathcal{F}_a$ instead peak at 60%. Using this method, we map $\mathcal{F}_a$ against HEMT LNA dc power consumption for each device. $\mathcal{F}_a$ does not simply saturate with increasing power. For several devices it declines above a device-dependent power well below typical operating points. For the 60% device, which has the highest overall $\mathcal{F}_a$, about 1~mW is needed to maintain $\mathcal{F}_a > 85\%$. Across all four devices, $\mathcal{F}_a > 80\%$ is reached with as little as about 0.3~mW, roughly an order of magnitude below typical operating points. These results establish a qubit-referenced benchmarking methodology and provide practical guidance for amplifier selection and bias in power-constrained multi-qubit readout systems.
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Applied Physics

Boundary-induced medium mapping enables air-equivalent acoustic propagation and perfect absorption in water

Mingyu Duan, Xiangjun Peng, Ying-Jing Qian et al. (+1 more)

The extreme water-air impedance contrast (~3600) has long acted as a fundamental barrier separating airborne and underwater acoustics. Here, we overcome this barrier with flexible boundaries, which establish a direct physical mapping between disparate acoustic media, enabling a water-filled channel to emulate air-equivalent wave propagation. Through vibroacoustic coupling, the effective wave velocity is rescaled in an approximately nondispersive manner, producing slow waves with tunable attenuation. Leveraging this concept, we demonstrate broadband underwater sound absorption at a deep-subwavelength thickness approaching the causal limit. Our findings reveal that acoustic media can be reshaped via boundary dynamics rather than bulk composition, paving the way for transplanting acoustic functionalities and metamaterial design across distinct media.
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All authors Mingyu Duan, Xiangjun Peng, Ying-Jing Qian, Tian Jian Lu

Applied Physics

Physics-Constrained Inverse Estimation of Irradiation-Induced Strain in He-H Ion-Implanted 4H-SiC Using Nanoindentation and Finite Element Modeling

M. Bensalem, N. Daghbouj, J.Duchon et al. (+8 more)

Nanoindentation is widely used to evaluate the mechanical properties of irradiated materials however its potential for quantifying irradiation induced subsurface strain remains underexplored. In this work, an integrated experimental numerical framework based on a physics constrained inverse modeling approach is employed to estimate the magnitude of a depth dependent irradiation induced strain distribution in single crystal 4H SiC following sequential He and H ion implantation. The approach combines depth sensing nanoindentation, finite element modeling FEM, and a simplex based inverse optimization routine to calibrate a physically motivated eigenstrain profile derived from ion damage simulations. The strain field is assumed to follow a lognormal distribution consistent with independently determined damage profiles SRIM, and is implemented in the FEM model through a depth dependent thermal expansion formulation. By minimizing the squared error between simulated and experimental force displacement curves, the peak tensile strain is estimated to be 0.91, accompanied by an effective Young s modulus of 310 GPa and a yield strength of 16.4 GPa. Independent validation using nano beam precession electron diffraction N PED confirms good agreement between the reconstructed and experimentally measured out of plane strain profiles in both magnitude and spatial distribution. The results demonstrate that nanoindentation, when combined with physics based inverse modeling, can provide a practical tool for quantifying irradiation-induced strain and residual stress in nuclear ceramics. This methodology offers a complementary approach to diffraction based techniques for assessing subsurface damage in ion irradiated materials relevant to advanced nuclear systems.
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All authors M. Bensalem, N. Daghbouj, J.Duchon, B.S. Li, A.T. AlMotasem, S. Magalhaes, A. Yie, F. Munnik, Xin Ou, W.J. Weber, T. Polcar

Applied Physics · Cross-listed from physics.optics

Broad-angle photon-pair generation from flatband quasi-BIC resonant 3R-MoS$_{2}$ metasurfaces

Tingting Liu, Huifu Qiu, Xintong Shi et al. (+2 more)

Spontaneous parametric down-conversion (SPDC) in ultrathin optical resonant metasurfaces offers a promising platform for integrated quantum light sources. However, conventional resonances suffer from steep momentum dispersion, limiting photon-pair generation to narrow excitation and emission angles. Here, we demonstrate a flatband-resonant 3R-MoS$_{2}$ metasurface for high-efficiency, broad-angle SPDC photon-pair generation. By implementing a supercell symmetry-breaking strategy via Brillouin zone folding, we achieve a flatband quasi-bound states in the continuum (quasi-BICs) resonance in the near-infrared regime that maintains a robust quality factor across a wide range of incident angle. Exploiting the strong local electric field enhancement of resonance and the large second-order susceptibility of 3R-MoS$_{2}$, the metasurface boosts the degenerate SPDC pair-generation rate with orders of magnitude enhancement over an unpatterned film of identical thickness. Crucially, the near-zero band dispersion extends the effective emission angle to $\pm 5^{\circ}$ with negligible spectral drift $\sim 0.1$ nm and high directional tolerance. Under pulsed excitation with a finite spectral bandwidth, the photon pair yield remains high, demonstrating strong spectral locking to the quasi-BIC resonance against pump detunings. This work establishes a versatile strategy for momentum-independent quantum light sources, opening new avenues for scan-free quantum ghost imaging and spatial-frequency quantum processing.
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All authors Tingting Liu, Huifu Qiu, Xintong Shi, Jumin Qiu, Shuyuan Xiao

Sunday 6 September

Applied Physics · Cross-listed from cond-mat.mtrl-sci

$\beta-(Al_{0.19} Ga_{0.81})_2 O_3/Ga_2 O_3$ Modulation-Doped Field-Effect Transistors with $>$ 6 kV Breakdown

Julian Gervassi Saga, Joshua T Buontempo, Nabasindhu Das et al. (+3 more)

$\beta-(Al_{0.19} Ga_{0.81})_2 O_3/Ga_2 O_3$ modulation-doped field-effect transistors (MODFETs) incorporating a high-quality Al2O3 gate dielectric and SiNx passivation are demonstrated for high-voltage operation. The devices exhibited a maximum drain current of 54 mA/mm, an on-resistance of 149 Ohm.mm, a minimum subthreshold slope of 94 mV/dec, and an ION/IOFF ratio exceeding $10^8$. Three-terminal breakdown measurements performed in Flourinert demonstrated a breakdown voltage that increased with gate-drain spacing, reaching 6.6 kV for a device with LGD = 28 microns. The corresponding average lateral electric field approached 2.4 MV/cm, while a power figure of merit of 222 MW/cm2 was achieved. To the best of the authors knowledge, the demonstrated breakdown voltage represents the highest reported value for a $\beta-(Al_x Ga_{1-x})_2 O_3/Ga_2 O_3$ MODFET and highlights the potential of modulation-doped $\beta$-Ga2O3 heterostructures for next-generation multi-kV power devices.
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All authors Julian Gervassi Saga, Joshua T Buontempo, Nabasindhu Das, Advait Gilankar, Hari P Nair, Nidhin Kurian Kalarickal

Saturday 5 September

Applied Physics · Cross-listed from physics.atom-ph

Floquet Interpretation of Avoided Crossings in AC Stark-Shifted Rydberg-EIT Spectra

Rajavardhan Talashila, Nikunjkumar Prajapati, Noah Schlossberger et al. (+1 more)

We present a combined experimental and Floquet-theoretical study of avoided crossings in the AC Stark-shifted electromagnetically induced transparency (EIT) spectra of Rydberg atoms. Observed avoided-crossing structures cannot be fully explained by conventional AC Stark maps alone, which provide the energy shifts but do not reveal the underlying state composition and coupling pathways. Using the Shirley method, we analyze the Floquet eigenstates to establish a direct connection between the measured spectra and the underlying dressed-state dynamics. By tracking the evolution of state mixing, bare-state composition, and dominant higher-order Floquet coupling pathways, we reveal the physical mechanisms responsible for the formation of avoided crossings across different principal quantum numbers and RF frequencies. Our results demonstrate that Floquet-eigenstate analysis provides a powerful framework for interpreting complex AC Stark-shifted Rydberg-EIT spectra and the underlying higher-order Floquet coupling interactions.
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All authors Rajavardhan Talashila, Nikunjkumar Prajapati, Noah Schlossberger, Christopher L. Holloway

Applied Physics · Cross-listed from cond-mat.soft

In situ local learning of dynamic network materials

Shuaifeng Li and Xiaoming Mao

Functional materials realize functionalities through pre-designed structures, whereas physical neural networks are trained by prescribing input-output behavior. Unifying these views would allow materials to acquire functions directly from dynamical tasks. Here we introduce an in situ local learning framework for dynamic network materials. A forward drive and a time-reversed adjoint error drive are applied to the same mechanical network, enabling the material to compute gradients of a time-domain loss through its own dynamics. The resulting update rules are local, compatible with the principle of physical learning. Each bond or node requires only co-located forward and adjoint fields. The method trains spring constants, nodal masses, bond damping coefficients and nodal damping coefficients, and programs dynamical functions including broadband wave cloaking, evanescent-wave imaging, passive transient output enhancement and vowel classification. These examples involve distinct physical mechanisms, such as wave scattering, near-field information transfer, dissipative non-normal dynamics and machine learning, but are obtained by simply changing the loss function, rather than leveraging expert knowledge. Therefore, dynamic network materials can act both as programmable matter and as physical neural networks, providing a route to material systems that learn temporal responses in situ.
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Applied Physics · Cross-listed from cond-mat.mes-hall

Large Nernst effect in chemically derived multilayer graphene at millitesla magnetic fields

Valentin Semkin, Denis Borisenko, Yana Litun et al. (+4 more)

Simple synthesis of graphitic compounds, their high conductivity, and integrability with other materials motivate the effort toward graphite-based thermoelectric generators. At the same time, semimetallic nature of graphite and graphene results in nearly-zero thermopower due to electron-hole compensation. Here, we observe large transverse thermopower in chemically derived multilayer graphene films with strong fluctuations of thickness and carrier density at low magnetic fields $B$. Using the scanning laser-induced heating of macroscopic film, we find that transverse (Nernst) thermoelectric voltage becomes comparable to the longitudinal thermoelectric voltage at the metal-doped graphene contact at $B^*\approx4$ mT and ambient conditions. Estimates of transverse thermopower $S_{xy}$ based on the known laser-induced temperature show that it is as large as $\sim 10$ $\mu$V/K at $B^*$, and raises in a sub-linear fashion to 250 $\mu$V/K at $B\approx315$ mT, the maximum field we reach with centimeter-sized permanent magnet. Extra increase in thermoelectric signal is achieved upon voltage measurement at Hall probes when the dc field lines are co-directional with local Nernst current. Our results show the promise of large-scale multilayer graphene for thermoelectricity generation.
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All authors Valentin Semkin, Denis Borisenko, Yana Litun, Oleg Kononenko, Dmitry Mylnikov, Alexey Bocharov, Dmitry Svintsov

Friday 4 September

Applied Physics · Cross-listed from cond-mat.mes-hall

Spectroscopy With Intelligent Feature Tracking for automated characterization of excited-state structure in semiconductor quantum dot devices

A. R. Huffman, Daniel Schug, Merritt Losert et al. (+6 more)

The characterization of excited-state structure in semiconductor quantum dot (QD) devices is an important component of tuning them for spin-qubit operation. We present Spectroscopy With Intelligent Feature Tracking (SWIFT), a framework that combines machine-learning (ML)-assisted feature identification with physics-informed geometric processing to extract energy-level splittings from pulsed-gate spectroscopy data. SWIFT isolates the relevant spectral features and exploits their characteristic geometry to reduce the two-dimensional spectroscopy analysis to a one-dimensional peak-detection problem. It further combines an ensemble-based confidence metric with sequential accumulation of rapid, low-SNR scans, allowing the inferred spectrum to be reevaluated as experimental evidence accumulates. Using Si/SiGe QD devices, we demonstrate SWIFT both offline and in real time, including automated tracking of QD excited states and lead resonances. Benchmarking on 255 manually labeled scans shows that SWIFT reduces the median splitting error to 0.05 mV from 0.11 mV for a classical baseline, with the largest improvement on lower-quality measurements. These results provide a path toward incorporating excited-state spectroscopy into autonomous QD characterization, tuning, and optimization, which will be essential in large-scale quantum dot devices.
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All authors A. R. Huffman, Daniel Schug, Merritt Losert, Sanghyeok Park, Daniel King, Yuna Chun, Giordano Scappucci, M. A. Eriksson, Justyna P. Zwolak

Applied Physics · Cross-listed from physics.ins-det

Nanoscale NMR of DNA-Functionalized Diamond Using Individual NV Centers

Erika Janitz, Konstantin Herb, Laura A. Völker et al. (+2 more)

Nuclear magnetic resonance (NMR) spectroscopy is a powerful probe of molecular structure and dynamics but typically requires large spin ensembles. Here, we demonstrate nanoscale NMR detection of fluorinated DNA using individual near-surface nitrogen-vacancy (NV) centers in diamond nanopillar waveguides under ambient conditions. We covalently tether $^{19}$F-labeled oligonucleotides to mixed nitrogen- and oxygen-terminated surfaces, localizing target spins within the nanoscale sensing volume. Probabilistic spin simulations suggest that the measured signals are consistent with those expected from a few molecules and depend strongly on NV-molecule separation, configuration, and local surface heterogeneity. These results establish a framework for NMR of surface-tethered biomolecules and identify key challenges for single-molecule structural elucidation.
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All authors Erika Janitz, Konstantin Herb, Laura A. Völker, Christian L. Degen, John M. Abendroth

Applied Physics

Thermoelectric properties of metal-semiconductor percolation composites

Oleksandr Porubaniyi, Sergii Tomko, Mihailo Cherkez et al. (+2 more)

We analyze thermoelectric response of composite materials comprising homogeneous semiconductor hosts with randomly distributed metallic inclusions. We demonstrate that the properties of such materials are strongly affected by the percolation transition (with background conductivity). We show that in vicinity of percolation threshold, the power factor and the thermoelectric figure of merit strongly depend on both the concentration and arrangement of inclusions. Finally, we identify promising regimes for enhancing the power factor in realistic composites.
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All authors Oleksandr Porubaniyi, Sergii Tomko, Mihailo Cherkez, Viktor Podolskiy, Radion Cherkez