Medical Physics
Vector Flow Imaging in Layered Models With a High Speed of Sound Contrast Using Pulse-Echo Ultrasound and Photoacoustics
Caitlin Smith, Guillaume Renaud, Kasper van Wijk et al. (+1 more)
In this study, we develop vector flow imaging techniques for multi-layered models with a high wavespeed contrast using photoacoustic and ultrasonic imaging. We use refraction-corrected delay-and-sum image reconstruction (RC-DAS), which enforces Snell's law to accurately calculate time delays within each layer. We compare RC-DAS against conventional delay-and-sum for vector flow imaging in benchtop phantoms made of transparent polymethyl methacrylate (PMMA) in a water bath. We study the flow beneath a PMMA layer using two phantoms, where the PMMA layer has different shapes and thicknesses. We image a slow-moving suspension of carbon microspheres (~4 mm/s) using interleaved photoacoustic and multi-angle plane wave ultrasound acquisitions measured with a 7.6 MHz linear ultrasound array. Photoacoustic waves are generated by a 1064 nm wavelength nanosecond-pulsed
laser at 50 Hz, and multi-angle plane wave ultrasound data are acquired at 100 Hz for eleven steering angles between $\pm$10$^\circ$. RC-DAS improves the flow speed accuracy, reducing the mean absolute error by 0.41-0.63 mm/s compared to the expected flow profile. The error in direction estimates improves when we use RC-DAS, with the interdecile range reducing by up to 17$^\circ$. This work emphasises the importance of refraction correction for accurate flow measurements in layered media with photoacoustics and ultrasonic imaging. While both imaging modalities can quantify flow in these multi-layered models, the modality best suited for a specific application will depend on the imaging target and flow dynamics. These techniques show promise for biomedical applications such as intraosseous and transcranial blood flow quantification, and in nondestructive testing to monitor fluid motion.
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All authors Caitlin Smith, Guillaume Renaud, Kasper van Wijk, Jami Shepherd
Optics
Ultrasensitive Polarization-Resolved Probing of Transient Dynamics in MoS$_2$ on Silicon Nitride Microresonators
Ramesh Kudalippalliyalil, Gyan Prakash, Christopher Munley et al. (+2 more)
We present an ultrasensitive technique for probing transient optical changes in atomically thin molybdenum disulfide (MoS$_2$) layers integrated onto silicon nitride (Si$_3$N$_4$) ring resonators. The MoS$_2$ is illuminated by a femtosecond
laser, while a tunable near-infrared (NIR) continuous-wave
laser probes the microresonator resonance. The NIR light polarization can be adjusted to either transverse electric (TE, parallel to the 2D material) or transverse
magnetic (TM, perpendicular), a configuration that is impossible to achieve with conventional normal-incidence pump-probe techniques. By capturing the transmitted signal on a fast oscilloscope, we detect transient optical shifts with unprecedented sensitivity, observing phenomena over time scales ranging from picoseconds to microseconds. Our results reveal both a rapid, carrier-induced nonlinear optical shift in the resonance, and a slower thermo-optic transient. The ability to simultaneously measure these fast and slow dynamics offers new insight into the complex optoelectronic behavior of 2D materials when integrated with microresonators. This method provides a significant advance over traditional pump-probe approaches, enabling the detection of exceedingly small transient signals and opening new avenues for exploring the optical properties of atomically thin materials. Our findings highlight the potential of this approach for investigating polarization-dependent nonlinear effects, with applications in photonics, sensing, and optoelectronics.
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All authors Ramesh Kudalippalliyalil, Gyan Prakash, Christopher Munley, Karen E. Grutter, Thomas E. Murphy
Chemical Physics
Multiply charged uranium monoxide as a versatile probe of fundamental physics
Jonas Stricker, Konstantin Gaul, Paul Fischer et al. (+8 more)
Multiply charged actinide molecules provide a unique platform to study fundamental physics and the chemical bond under extreme conditions. Beyond the inherently large relativistic effects associated with a high
proton number $Z$, an increased molecular charge can further enhance the electronic sensitivity to
symmetry-violating
nuclear effects, including
nuclear Schiff moments. Experimental investigations of multiply charged actinide molecules are challenging because the high charges severely destabilize chemical bonds, leading to spontaneous Coulomb explosion. We demonstrate a method to systematically generate and detect molecular ions at the edge of chemical stability. By applying high-fluence
laser ablation to a depleted uranium metal foil, we produce atomic uranium ions U$^{z+}$ and uranium monoxide cations UO$^{z+}$ with $z = 1$–4. Among them, we observe UO$^{3+}$ and UO$^{4+}$, which exhibit comparatively simple electronic structures and are therefore promising for precision spectroscopy. The experiments are supported by relativistic density functional theory calculations of
equilibrium bond lengths, charge distributions, and binding energies of all observed molecules. Calculations of
symmetry-violating properties suggest a pronounced sensitivity of UO$^{3+}$ to hadronic $CP$ violation. This approach opens a pathway for high-precision investigations of fundamental
symmetries and the exploration of relativistic actinide chemistry in previously inaccessible regimes.
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All authors Jonas Stricker, Konstantin Gaul, Paul Fischer, Lennard M. Arndt, Florian Kraus, David Krug, Dennis Renisch, Ferdinand Schmidt-Kaler, Lutz Schweikhard, Jean Velten, Christoph E. Düllmann
Accelerator Physics
3D Printing as a Rapid Prototyping Approach for Novel RF Cavity Designs
David Sims, Benjamin Sims, Brian Wright et al. (+2 more)
3D-printing of radiofrequency (RF) cavity resonators could provide a cost-effective solution that enables rapid prototyping and design flexibility compared to traditional fabrication of full-metal cavities. In this work, the feasibility of fabrication of a useful multi-mode GHz cavity is explored. Two kinds of plastics, two slicing approaches and two metal coating techniques were used to build a series of clamped cavities with thin inner copper surface on otherwise 3D printed plastic surface. The cavities were then bench-tested to identify spatial field distributions, operating frequencies and quality factors (Q-factor). Pros and cons of the used fabrication approaches were identified and understood, and the performance of longitudinally sliced painted cavity design demonstrated considerable practicality of 3D-printing approach in designing rf systems.
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All authors David Sims, Benjamin Sims, Brian Wright, John W. Lewellen, Sergey V. Baryshev
Atmospheric and Oceanic Physics
Effects of Climate Change on Moroccan Coastal Upwelling: Relationships between the NAO, Upwelling Index, and Sea Surface Temperature (1978-2024)
Mohammed El Abdioui
This study investigates
climate change impacts on Moroccan Atlantic coastal upwelling (21$^{\circ}$–35$^{\circ}$N), analyzing interrelationships among the North Atlantic Oscillation (NAO), Coastal Upwelling Index (CUI), and Sea Surface Temperature (SST) from 1978–2024 using ERA5 reanalysis data. Methods include index calculations, seasonal correlations, Granger causality tests, linear trends, and breakpoint detection to evaluate spatio-temporal dynamics and causality. Results reveal seasonal variability: strong NAO–CUI coupling in winter (DJF; $r = +0.65$), local upwelling dominance in summer (JJA; $r = -0.46$ CUI–SST), and a north–south gradient with intense southern upwelling (mean Ekman transport $37.1 \pm 34.5$ m$^3$/s/100m). Trends show significant SST warming ($+0.0736$ units/decade; $+0.149^{\circ}$C/decade spatially), summer upwelling decline ($-0.0635$ units/decade in JJA), and weak NAO shifts. Granger causality indicates rapid local forcing (CUI $\to$ SST, lag 1–3 months), delayed teleconnections (NAO $\to$ SST, lag 2–4 months), and ocean feedback (SST $\to$ NAO, lag 7–11 months). Breakpoints (1992–1997) signal warming acceleration, highlighting a paradox of global SST rise amid localized upwelling-induced cooling per Bakun's hypothesis. Findings underscore implications for fisheries, aquaculture, and tourism, advocating adaptive management via seasonal
forecasting. Keywords: Coastal upwelling, NAO, SST,
climate change, Granger causality, Moroccan Atlantic, Ekman transport, spatio-temporal variability.
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Atmospheric and Oceanic Physics
Predicting Forecast Error for the HRRR Using LSTM Neural Networks: A Comparative Study Using New York and Oklahoma State Mesonets
David Aaron Evans, Kara J. Sulia, Nick P. Bassill et al. (+3 more)
Long Short-Term
Memory (LSTM) models are trained to predict forecast errors for the High-Resolution Rapid Refresh (HRRR) model using the New York State Mesonet and Oklahoma State Mesonet near-surface weather observations as ground truth. When evaluated using mean-absolute-error and percent improvement relative to the HRRR, LSTMs predict precipitation error most accurately, providing, on average, a 48% improvement relative to the HRRR forecast, followed by wind error, providing, on average, a 15% improvement, and then temperature error, providing, on average, a 25% improvement. Precipitation errors exhibit an asymmetry, with overforecast precipitation detected more accurately than underforecast, while wind error predictions are consistent across over- and underforecast predictions. Temperature error predictions are relatively accurate but smoother, with respect to variance, than true observations. This paper describes an overview of LSTM performance with the expressed intent of providing forecasters with real-time predictions of forecast error at the point of use within the New York State and Oklahoma State Mesonets. In practice, the predicted errors can be used to adjust deterministic HRRR forecasts at the point of use, identify locations and variables with elevated uncertainty, and provide supplemental guidance for high-impact decision-making. This research demonstrates the potential of LSTM-based machine learning models to provide actionable, location-specific predictions of forecast error for high-resolution operational numerical weather prediction (NWP) systems. However, model performance is variable-dependent, and the approach relies on the availability of dense mesonet observations, which may limit applicability in data-sparse regions.
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All authors David Aaron Evans, Kara J. Sulia, Nick P. Bassill, Chris D. Thorncroft, Jay C. Rothenberger, Lauriana C. Gaudet
Atomic Physics
Hyperfine spectroscopy of optical-cycling transitions in singly ionized thulium
Patrick Müller, Andrei Tretiakov, Amanda Younes et al. (+3 more)
We present a spectroscopic investigation of $^{169}\mathrm{Tm}^+$ that provides two key foundations for its use as a platform for advanced
quantum applications. First, we establish the complete spectroscopic road map for optical cycling (including
laser cooling) by performing high-resolution spectroscopy on $^{169}\mathrm{Tm}^+$ ions in an ion trap. We characterize the primary $313\,\mathrm{nm}$ and complementary $448/453\,\mathrm{nm}$ cycling transitions, identify the essential near-infrared repumping frequencies, and determine the
magnetic-dipole hyperfine $A$ constants for all relevant levels. Second, we report a detailed characterization of a metastable state as a candidate for hosting a robust
qubit, performing lifetime measurements and Zeeman-resolved microwave hyperfine spectroscopy with $\mathrm{kHz}$ precision.
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All authors Patrick Müller, Andrei Tretiakov, Amanda Younes, Nicole Halawani, Wesley C. Campbell, Paul Hamilton
Accelerator Physics
Bridging the Gap Between Modern UX Design and Particle Accelerator Control Room Interfaces
Rachael Hill, Casey Kovesdi, Torrey Mortenson et al. (+3 more)
Accelerator control systems often represent relatively complex and safety-sensitive human-machine interfaces within process control industries. These systems are technically robust and reflect the cumulative integration of solutions built and adapted across decades. One of the regular, unfortunate casualties of provisional accelerator control system updates is their human-system interfaces (HSIs) which often lag behind modern usability and design standards. An additional challenge is that although there is a multitude of established human factors (HF), and user experience (UX) principles for everyday digital applications, there are very few (if any) established principles for complex and safety-critical applications for an accelerator. This paper argues for the importance of established HF and UX principles (herein referred to as human-centered design principles) into the development of accelerator HSIs, emphasizing the need for clarity, consistency, responsiveness, and cognitive accessibility. Drawing from HF/UX best practices and human-centered design, this paper discusses how these approaches can enhance operator performance, reduce human error, and improve accelerator personnel collaboration. Case studies from Accelerator Control Operations Research Network (ACORN) at Fermilab are explored to demonstrate how interfaces built with human-centered design principles can scale with system complexity while remaining intuitive and efficient for diverse user roles including operators, machine experts, and engineers. By bridging the gap between traditional control system design and modern human-centered design methods, this paper provides a roadmap for evolving accelerator HSIs into more usable, maintainable, and effective tools.
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All authors Rachael Hill, Casey Kovesdi, Torrey Mortenson, Madelyn Polzin, Zachary Spielman, Katya Le Blanc
Computational Physics · Cross-listed from math.NA
Accuracy of the Yee FDTD Scheme for Normal Incidence of Plane Waves on Dielectric and Magnetic Interfaces
Pavel A. Makarov and Vladimir I. Shcheglov
This paper analyzes the accuracy of the standard Yee finite-difference time-domain (FDTD) scheme for simulating normal incidence of harmonic plane waves on planar interfaces between lossless, linear, homogeneous, isotropic media. Unlike prior analyses limited to dielectric interfaces, we provide a unified treatment encompassing both dielectric and
magnetic media. We consider two common FDTD interface models based on different staggered-grid placements of material parameters. For each, we derive discrete analogs of the Fresnel reflection and transmission coefficients by formulating effective boundary conditions that emerge from the Yee update equations. A key insight is that the staggered grid implicitly spreads the material discontinuity over a transition layer of one spatial step, leading to systematic deviations from exact theory. We quantify these errors via a transition-layer model and provide (i) qualitative criteria predicting the direction and nature of deviations, and (ii) rigorous error estimates for both weak and strong impedance contrasts. Finally, we examine the role of the Courant number in modulating these errors, revealing conditions under which numerical dispersion and interface discretization jointly influence accuracy. This analysis provides quantitative error estimates that are directly applicable to simulation practice, offers a transition-layer interpretation that bridges classical FDTD with modern immersed-interface methods, and establishes
benchmarks for validating structure-preserving discretizations of Maxwell's equations.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Kagome Topology in Two-Dimensional Noble-Metal Monolayers
Carlos M. O. Bastos, Emanuel J. A. dos Santos, José A. dos S. Laranjeira et al. (+4 more)
Two-dimensional (2D) metallic
lattices with kagome
topology provide a unique platform for exploring the interplay between
geometric frustration, reduced coordination, and
lattice stability in elemental systems. Motivated by the recent experimental realization of atomically thin gold layers and kagome goldene, we present a first-principles investigation of free-standing kagome monolayers of Cu, Ag, and Au. Using density functional theory combined with
lattice dynamics and ab initio molecular dynamics, we systematically assess their structural, mechanical, dynamical, and thermal stability. All kagome monolayers satisfy the 2D Born criteria and exhibit relatively low in-plane stiffness compared to
graphene and hexagonal goldene, reflecting the porous nature of the kagome
lattice and its metallic bonding. Among the three systems, the Au-based
lattice displays the highest in-plane Young's modulus.
Phonon calculations reveal that the unstrained kagome phase is dynamically unstable for all metals. However, a moderate biaxial tensile strain of 5% stabilizes the Ag and Au monolayers, while Cu retains residual unstable modes. Finite-temperature simulations further show that Cu rapidly reconstructs toward a trigonal
lattice, Ag remains metastable at low temperature but collapses at room temperature, and Au exhibits competing kagome and trigonal motifs at 300 K, indicating near-degeneracy between these phases. These results establish that strain engineering and atomic size are key determinants of the stability of metallic kagome monolayers and provide guidance for future substrate-supported realizations.
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All authors Carlos M. O. Bastos, Emanuel J. A. dos Santos, José A. dos S. Laranjeira, Kleuton A. L. Lima, Alexandre C. Dias, Douglas S. Galvão, Luiz A. Ribeiro Jr
Biological Physics
Effects of cell-cell communication on bacterial chemotaxis
Soutick Saha, Sean Fancher and Andrew Mugler
Bacteria track chemical gradients using a biased random walk, a process called chemotaxis. Experiments suggest that bacteria also communicate during this process. Using a mathematical model, we find that sufficiently strong communication succeeds in keeping a population of bacteria together but slows down chemotaxis. However, if the secretion of the communication molecule is coupled to the detection of the external chemoattractant, chemotaxis can be faster than without communication. Intriguingly, in this regime we predict that, even though blocking the communication receptors should slow down chemotaxis, partially blocking or underexpressing them should speed it up. Our work provides physical insights on how communication and chemotaxis are connected and may help explain why chemotaxing bacteria communicate.
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Fluid Dynamics
The spatial organization of wind turbine wakes
Janka Lengyel, Stéphane G. Roux, Patrice Abry et al. (+4 more)
Wind turbine wakes play a central role in determining wind farm performance, yet their spatial organization remains only partially understood. Here, we apply a spatially localized multifractal analysis to quantify the strength of dependencies (local roughness) and extreme velocity fluctuations (local intermittency) in turbine wakes, and relate these properties to established metrics in wind energy research. Using two-dimensional nacelle-mounted
LiDAR plan-position-indicator scans, we extract scale-invariant features that enable systematic comparisons across the wake without requiring time-resolved data. Designed to robustly handle irregular sampling, our analysis yields four main findings: i.) Four distinct wake zones are identified, each exhibiting unique patterns of roughness and intermittency. ii.) Coherent, strongly correlated patches emerge 2 to 5 rotor diameters D downstream, with intermittency strengthening periodically at multiple D positions and along the wake-free-flow interface. iii.) The classical "intermittency ring" is consequently redefined as a set of localized "intermittency bubbles", iv.) which interact dynamically with the ambient atmosphere through an inverse energy cascade, transferring energy from small to large scales. These findings, supported by concurrent cup anemometer observations under free-inflow conditions, demonstrate that local multifractal analysis provides a robust and cost-effective diagnostic framework for wake characterization and wake-model validation, with direct relevance for wind-farm design and control.
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All authors Janka Lengyel, Stéphane G. Roux, Patrice Abry, Norman Wildmann, Julia Menken, Olivier Bonin, Jan Friedrich
Physics and Society
Predication of Final Medal Counts in Olympic Games by Monte Carlo Simulations
Maggie Barker, Daniel Guo, Justin Palmeri et al. (+1 more)
In the paper, a program strength model was proposed to evaluate the performance of countries across different Olympic events. The model assessed how strong a country's program was in each event and also factored in the influence of past Olympic performances. The final medal counts from the Paris 2024 Olympic Games were used to validate the model and to determine the optimal set of constants using Monte Carlo simulation. Based on this model, a prediction of the final medal counts for the 2028 Olympic Games is also provides for reference.
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All authors Maggie Barker, Daniel Guo, Justin Palmeri, and Ridge Shepherd
Fluid Dynamics
Sunia Tanweer and Firas A. Khasawneh
Aeroelastic flutter represents a critical nonlinear instability arising from the coupling between structural elasticity and unsteady aerodynamics. In deterministic settings, flutter onset is associated with bifurcations of invariant sets such as
equilibria or limit cycles. However, under
stochastic excitation, long-time system behavior is better described in terms of stationary probability distributions rather than trajectory-based attractors. In this work, we present a
topology-based framework to detect
stochastic (P-)bifurcations in a two-degree-of-freedom aeroelastic system with structural nonlinearity. The method operates on high-dimensional stationary distributions reconstructed via kernel density estimation (KDE) and characterizes their structure using persistent homology. We compare bifurcation behavior across three excitation models: sinusoidal perturbations, Dryden
turbulence, and von Karman
turbulence. While conventional time-domain and phase-space analyses reveal only modest differences between these models, the proposed homological bifurcation plots detect consistent shifts in bifurcation onset and topological structure. The approach enables automated and scalable analysis of
stochastic bifurcations in complex dynamical systems.
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Instrumentation and Detectors · Cross-listed from eess.IV
Configurable {\gamma} Photon Spectrometer to Enable Precision Radioguided Tumor Resection
Rahul Lall, Youngho Seo, Ali M. Niknejad et al. (+1 more)
Surgical tumor resection aims to remove all cancer
cells in the tumor margin and at centimeter-scale depths below the tissue surface. During surgery, microscopic clusters of disease are intraoperatively difficult to visualize and are often left behind, significantly increasing the risk of cancer recurrence. Radioguided surgery (RGS) has shown the ability to selectively tag cancer
cells with gamma ({\gamma})
photon emitting radioisotopes to identify them, but require a mm-scale {\gamma}
photon spectrometer to localize the position of these
cells in the tissue margin (i.e., a function of incident {\gamma}
photon energy) with high specificity. Here we present a 9.9 mm2 integrated
circuit (IC)-based {\gamma} spectrometer implemented in 180 nm CMOS, to enable the measurement of single {\gamma}
photons and their incident energy with sub-keV energy resolution. We use small 2 2 um reverse-biased diodes that have low depletion region capacitance, and therefore produce millivolt-scale voltage signals in response to the small charge generated by incident {\gamma}
photons. A low-power energy spectrometry method is implemented by measuring the decay time it takes for the generated voltage signal to settle back to DC after a {\gamma} detection event, instead of measuring the voltage drop directly. This spectrometry method is implemented in three different pixel architectures that allow for configurable pixel sensitivity, energy-resolution, and energy dynamic range based on the widely heterogenous
surgical and patient presentation in RGS. The spectrometer was tested with three common {\gamma}-emitting radioisotopes (64Cu, 133Ba, 177Lu), and is able to resolve activities down to 1 uCi with sub-keV energy resolution and 1.315 MeV energy dynamic range, using 5-minute acquisitions.
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All authors Rahul Lall, Youngho Seo, Ali M. Niknejad, Mekhail Anwar
Atmospheric and Oceanic Physics
WaveSim: A Wavelet-based Multi-scale Similarity Metric for Weather and Climate Fields
Gabriele Accarino, Viviana Acquaviva, Sara Shamekh et al. (+2 more)
We introduce WaveSim, a multi-scale similarity metric for the evaluation of spatial fields in weather and
climate applications. WaveSim exploits wavelet transforms to decompose input fields into scale-specific wavelet coefficients. The metric is built by multiplying three orthogonal components derived from these coefficients: Magnitude, which quantifies similarities in the energy distribution of the coefficients, i.e., the intensity of the field; Displacement, which captures spatial shift by comparing the centers of mass of normalized energy distributions; and Structure, which assesses pattern organization independent of location and amplitude. Each component yields a scale-specific similarity score ranging from 0 (no similarity) to 1 (perfect similarity), which are then combined across scales to produce an overall similarity measure. We first evaluate WaveSim using synthetic test cases, applying controlled spatial and temporal perturbations to systematically assess its sensitivity and expected behavior. We then demonstrate its applicability to physically relevant case studies of key modes of
climate variability in Earth System Models. Traditional point-wise metrics lack a mechanism for attributing errors to physical scales or modes of dissimilarity. By operating in the wavelet domain and decomposing the signal along independent axes, WaveSim bypasses these limitations and provides an interpretable and diagnostically rich framework for assessing similarity in complex fields. Additionally, the WaveSim framework allows users to place emphasis on a specific scale or component, and lends itself to user-specific model intercomparison, model evaluation, and calibration and training of
forecasting systems. We provide a PyTorch-ready implementation of WaveSim, along with all evaluation scripts, at: https://github.com/gabrieleaccarino/wavesim.
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All authors Gabriele Accarino, Viviana Acquaviva, Sara Shamekh, Duncan Watson-Parris, David Lawrence
Chemical Physics
Electrodrying in nanopores: from fundamentals to iontronic and memristive applications
Giovanni Di Muccio, Gonçalo Paulo, Lorenzo Iannetti et al. (+3 more)
Iontronics is a burgeoning paradigm that employs ions in solution as information carriers for sensing and computing, e.g., in neuromorphic devices. The fundamentally different working principle as compared to electronics requires novel approaches and concepts to control the impedance of nanoscale fluidic
circuit elements, such as nanopores. For instance, previous research has focused on voltage-induced pore wetting as a means to trigger conduction in nanopores. The present study explores the opposite counter-intuitive mechanism: using voltage to dry hydrophobic nanopores and, therefore, to turn off conduction. This "electrodrying" concept affords exquisite, bidirectional control over the conductance of nanopores additionally showing hysteresis in the current-voltage curve that is the fingerprint of memristors. Using an analytical model and free-energy molecular dynamics simulations, we explain the physical mechanism underlying electrodrying and provide clear design criteria for solid-state and biological nanopores with bidirectional control over conductance. The electrical behaviour of electrodrying nanopores shows two unique features: i) the hysteresis loop is shifted from the origin, accounting for the fifth, previously unreported memristor type and ii) negative differential resistance is observed over a broad voltage range in which the non-conductive state is favoured by electrodrying. These properties are demonstrated in a short-term
memory task and in an iontronic oscillator
circuit to showcase their potential in neuromorphic applications and iontronic devices. Finally, we validate our predictions through experiments on engineered dipolar hydrophobic CytK nanopores, whose voltage-dependent conductance substantiates the electrodrying concept.
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All authors Giovanni Di Muccio, Gonçalo Paulo, Lorenzo Iannetti, Adina Sauciuc, Giovanni Maglia, Alberto Giacomello
Chemical Physics
Mapping the Optical Landscape of a Squaraine Molecule in the Visible and Ultraviolet Energy Range
Narges Taghizade, Robert Schwarzl, Frederik Leinenbach et al. (+9 more)
Although squaraine dyes are commonly praised as candidates for light-based applications, little is known about their excited state landscape beyond the low-energy visible light region. Our work aims for an improved understanding of the photophysical properties of squaraines at the example of N-isobutyl substituted anilino-squaraine (SQIB) by extending ground-state and excited-state absorption spectroscopy of the molecule into the ultraviolet up to 6.5~eV. In addition, we distinguish the relative transition dipole moments of the excited state absorption peaks with the help of transient absorption anisotropy experiments. To relate experimental features to specific states, we employ a set of ab initio methods including time-dependent density functional theory (TDDFT), the Bethe-Salpeter equation (BSE) and n-electron valence perturbation theory on top of a self-consistent complete active space (CASSCF/NEVPT2). Our assignment is complemented by vibronic simulations and a discussion of two-
photon absorption measurements. Through this joint effort, we are able to provide a consistent picture of the optical behavior of SQIB across the visible and ultraviolet light regime, and assign a total of twelve electronically excited states to our experimental data.
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All authors Narges Taghizade, Robert Schwarzl, Frederik Leinenbach, Maximilian Jeindl, Marvin F. Schumacher, Brunella Bardi, Arne Lützen, Manuela Schiek, Andreas W. Hauser, Peter Puschnig, Markus Koch, Andreas Windischbacher
Optics
Field localisation and spin-momentum locking in zero-dimensional dissipative topological photonic interface state
Aidan H.Y. Chong, Y.Q. Liu, C. Liu et al. (+1 more)
Topological photonic systems support edge states that are robust against disorder and perturbation. Depending on the
symmetry and dimensionality of the bulk systems, different edge states emulating
soliton,
quantum integer and
quantum spin Hall effects have been realized. A major concern in photonics is how one can shape the strength and polarisation of electromagnetic fields to suit different applications. Here, we show zero-dimensional (0D) interface state arising from one-dimensional (1D) dissipative topological photonic
crystals exhibit strong field localisation and
spin-momentum locking thanks to its complex classical analogue Dirac mass parameter. By using spatiotemporal coupled mode theory to formulate 1D photonic
crystals and their corresponding Jackiw Rebbi-like (JR) interface state, we find the interaction between two energy bands at high
symmetry points plays a major role in defining not only the topological triviality of the
crystals but also its complex Dirac mass parameter. More importantly, when two topological trivial and nontrivial bulk systems are brought together to form a JR state, while the real part of the Dirac mass parameter governs the spectral and spatial field localisations of the interface state, the imaginary part gives rise to a net flow of energy towards the interface and a transverse
spin angular momentum, resulting in a strong
spin-momentum locking. We verify our theory by 1D plasmonic
crystals using finite-difference time-domain simulations as well as far-field angle-resolved spectroscopy and imaging.
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All authors Aidan H.Y. Chong, Y.Q. Liu, C. Liu, Daniel H.C. Ong
Atomic Physics
Engineering Zeeman-manifold quintets using state-dependent light shifts in neutral atoms
Benedikt Heizenreder, Bas Gerritsen, Katya Fouka et al. (+4 more)
We present a general method for engineering qudits through individually addressable transitions between Zeeman sublevels, achieved by combining a large linear Zeeman shift with a state-dependent light shift. This approach lifts the degeneracy between adjacent states while simultaneously tuning their energy splittings into the
radio-frequency (RF) domain, enabling coherent manipulation within the Zeeman
manifold using experimentally accessible drive frequencies. As a concrete realization, we investigate the implementation of an $SU(5)$ quintet encoded in the Zeeman sublevels of the long-lived $^3\mathrm{P}_2$ state of neutral $\mathrm{^{88}Sr}$ atoms confined in far-detuned, $\sigma^{-}$-polarized optical tweezers. Using realistic experimental parameters, we numerically demonstrate full control of the quintet
manifold, including initialization into a specific $SU(5)$ basis state via a multi-
photon transfer, coherent state- and site-selective single-qudit rotations driven by RF fields, and fast state-selective optical readout. Our simulations predict state-preparation fidelities of $\mathcal{F} \simeq 0.99$ within less than $1~$us, single-qudit gate fidelities of $F$ $\simeq 0.99$ with $\pi$-pulse durations of $\sim1.4~$us, and fast destructive imaging with durations below $10~$us under ideal conditions. These results establish a broadly applicable framework for high-fidelity control of Zeeman sublevel-encoded qudits and highlight the $^3\mathrm{P}_2$
manifold in strontium as a promising platform for scalable qudit-based
quantum technologies.
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All authors Benedikt Heizenreder, Bas Gerritsen, Katya Fouka, Robert J. C. Spreeuw, Florian Schreck, Arghavan Safavi Naini, Alexander Urech
Fluid Dynamics
Self-adaptive physics-informed neural network for forward and inverse problems in heterogeneous porous flow
Md. Abdul Aziz, Thilo Strauss, Muhammad Mohebujjaman et al. (+1 more)
We develop a self-adaptive physics-informed neural network (PINN) framework that reliably solves forward Darcy flow and performs accurate permeability inversion in heterogeneous porous media. In the forward setting, the PINN predicts velocity and pressure for discontinuous, piecewise-constant permeability; in the inverse setting, it identifies spatially varying permeability directly from indirect flow observations. Both models use a region-aware permeability parameterization with binary spatial masks, which preserves sharp permeability jumps and avoids the smoothing artifacts common in standard PINNs. To stabilize training, we introduce self-learned loss weights that automatically balance PDE residuals, boundary constraints, and data mismatch, eliminating manual tuning and improving robustness, particularly for inverse problems. An interleaved AdamW-L-BFGS optimization strategy further accelerates and stabilizes convergence. Numerical results demonstrate accurate forward surrogates and reliable inverse permeability recovery, establishing the method as an effective mesh-free solver and data-driven inversion tool for porous-media systems governed by partial differential equations.
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All authors Md. Abdul Aziz, Thilo Strauss, Muhammad Mohebujjaman, Taufiquar Khan
Instrumentation and Detectors
Hybrid Machine-Learning Particle Identification for the ePIC Proximity-Focusing RICH
D. H. Dongwi, C.-J. Naïm, L. Rhode et al. (+1 more)
We present a machine-learning-based particle-identification study for the proximity-focusing Ring Imaging Cherenkov (pfRICH) detector of the ePIC experiment at the Electron-Ion
Collider. Operating in the backward region ($-3.5 \lesssim \eta \lesssim -1.5$), the pfRICH is designed to achieve at least $3\sigma$ separation among pions, kaons, and
protons up to $7,\mathrm{GeV}/c$ for Semi-Inclusive Deep Inelastic Scattering measurements. Using a standalone Geant4 simulation of the pfRICH, we develop a hybrid machine-learning approach that combines convolutional neural-network-based feature extraction with gradient-boosted decision-tree classifiers. This method significantly enhances Cherenkov-ring pattern recognition and improves particle-separation performance, demonstrating the effectiveness of hybrid machine-learning techniques for next-generation Cherenkov detectors at the EIC.
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All authors D. H. Dongwi, C.-J. Naïm, L. Rhode, A. Deshpande
Optics
Microwave Controlled Photonic Spin Hall Effect in Atomic System and Microwave Electrometry
Muhammad Waseem
The photonic
Spin Hall Effect (SHE) causes a polarization dependent transverse shift of light at an interface. In this paper, we theoretically investigate the microwave controlled photonic SHE and microwave electrometry in a closed-loop $\Lambda$-type atomic system. At zero probe detuning ($\Delta_p = 0$) and relative phase $\phi=0,\pi$, the photonic SHE magnitude remains at the intrinsic finite beam saturation limit $w_0/2$, whereas the microwave field shifts its angular position linearly with opposite slopes (signs) for the two phases, enabling differential microwave electric field sensing. At $\phi=\pi/2$, the photonic SHE magnitude decays exponentially with $\Omega_\mu$, providing weak microwave electric field sensing. In contrast, at $\Delta_p = \pm \Omega_c$ (control field coupling), the photonic SHE reaches a maximum of half the incident beam waist when $\Omega_{\mu} \geq \Omega_p$ and the phase $\phi$ is optimized. Interestingly, we observed microwave controlled switching of photonic SHE by tuning the relative phase $\phi$ at an optimized value of $\Omega_{\mu}$ and $\Omega_{c}$. Our results may have potential applications in microwave
quantum sensing and
quantum optical switches based on the photonic SHE.
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Fluid Dynamics
An Ice Christmas Tree: Fast Three-Dimensional Printing of Ice Structures via Evaporative Cooling in Vacuum
Menno Demmenie, Stefan Kooij and Daniel Bonn
We demonstrate a novel approach to three-dimensional (3D) printing of freeform ice structures by exploiting evaporative cooling. A micrometer-sized water jet is used to 3D print inside a
vacuum chamber. The reduced ambient pressure leads to rapid evaporation of the extruded water, extracting latent heat, and quickly cooling the water well below 0 {\deg}C. Once deposited, the water freezes almost instantaneously into stable ice structures. We demonstrate high-fidelity printing of complex geometries (Christmas trees, cones, vertical pillars, and free-standing zigzag structures) without cryogenic infrastructure, supporting materials, or external refrigeration. This approach directly visualizes fundamental thermodynamic principles – latent heat, evaporative cooling, and pressure-dependent phase transitions – while offering a relatively simple and scalable platform for ice-templated microfluidics and tissue engineering, or even extraterrestrial 3D printing.
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Optics
Blue-shifted dispersive waves and broadband UV emission using dual-core SiN waveguides
L. Xia, P.J.M. van der Slot, M. Timmerkamp et al. (+2 more)
We show that using strongly coupled dual-core waveguides for supercontinuum generation shifts the wavelength of the high-frequency dispersive waves towards shorter wavelengths, as compared to generation in a single-core waveguide having the same core dimensions. In a demonstration experiment, we launch ultrashort infrared pump pulses at 1-$\mu$m wavelength (285-THz frequency) into silicon nitride waveguides, where
soliton formation and fission leads to generation of dispersive waves in the visible range. Efficient input coupling and controlled excitation of the fundamental supermodes of the dual-core waveguide is provided with adiabatic tapers and a dual-prong input structure. For the dual-core waveguide, the short-wavelength dispersive wave is located at 540~nm (green, 555~THz), which is blue-shifted by 80~nm (70~THz) compared to that of the single-core waveguide. Simultaneously, the dual-core waveguide generates broadband radiation spanning from the blue into the UV range, reaching to below 350~nm (above 855~THz), with typically a spectral density 25~dB below that of the dispersive wave. The broadband component can be addressed to third harmonic generation and is not observed in single-core supercontinuum generation. Numerical modeling shows good agreement with experimental measurements. The demonstrated dual-core approach and dedicated input coupling appear to hold promise also for other waveguide structures, independent of specific materials or core dimensions, by providing shorter wavelengths than with the respective single-core waveguide.
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All authors L. Xia, P.J.M. van der Slot, M. Timmerkamp, C. Fallnich, K.-J. Boller
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Accurate bandgaps of photovoltaic kesterites from first-principles DFT+U
Andrew C. Burgess, Lórien MacEnulty, Ethan D'Arcy et al. (+2 more)
Streamlined prediction of the electronic properties of photoactive materials warrants a Density Functional Theory (DFT) based approach that (i) yields reliable bandgaps, (ii) is free of empirically tuned parameters, and (iii) exhibits low computational overhead. Here we show that for Cu2ZnSnS4 and Cu2ZnGeS4 kesterite photovoltaic materials, all three of these demands are met by the DFT plus Hubbard U technique (DFT+U) with corrective parameters evaluated via minimum-tracking linear response. The predicted bandgaps are found to even marginally outperform those from the self-consistent GW approach. Key to this method's success is the application of Hubbard U corrections to all atomic subspaces that dominate the conduction and valence band edges, as opposed to the conventional approach of correcting 3d and 4f atomic states. Intriguingly, the inclusion of Hund's J corrections via the extended DFT+U+J functional significantly worsens these results. This under performance can be ameliorated through the use of the Burgess-Linscott-O'Regan (BLOR) flat-plane based Hubbard U plus Hund's J functional, with bandgap predictions in close agreement with the conventional DFT+U method. The DFT+U method is also used to predict defect-induced changes to the bandgap and associated formation energies, in 1,728-atom supercells.
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All authors Andrew C. Burgess, Lórien MacEnulty, Ethan D'Arcy, David Gavin, David D. O'Regan
Fluid Dynamics
Neural-Network Closures for Complex-Shaped Particles in the Force-Coupling Method
Marco Laudato
A data-driven surrogate framework to accelerate particle-resolved modelling of quasi-dilute suspensions of rigid, non-spherical particles in Stokes flow is introduced. A regularized-Stokeslet boundary element method (BEM) is implemented to compute hydrodynamic responses in canonical linear flows, focusing on the particle stresslet and angular velocity for spheroids, and additionally the
chiral thrust for helicoidal particles. For spheroids, the BEM solver is validated against available analytical
benchmarks (Faxen-type relations for the stresslet and Jeffery's theory for rotation), and parameter choices for surface discretization and regularization are selected through systematic convergence studies. For helicoidal particles, where no analytical solutions exist, accuracy is quantified via Richardson-style self-convergence, complemented by tests of linearity, frame objectivity, and chirality-dependent
symmetries. The resulting
datasets are used to train a neural-operator surrogate that maps local flow descriptors and particle configuration to the corresponding stresslet, rotation, and thrust at negligible evaluation cost. Across independent test sets spanning random orientations and flow types, the surrogate achieves median relative errors below 1% for the deviatoric stresslet (95th percentile below 3%) and comparable accuracy for angular velocity and thrust. The combination of validated BEM generation and fast inference provides a practical route to coupling complex particle shapes into mesoscale solvers such as the force-coupling method, enabling large-ensemble studies of microstructure and suspension rheology.
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Chemical Physics · Cross-listed from cond-mat.dis-nn
On the Boroxol Ring Fraction in Melt-Quenched B$_2$O$_3$ Glass
Debendra Meher, Nikhil V. S. Avula and Sundaram Balasubramanian
An atomistic structural model for melt-quenched B$_2$O$_3$ glass has eluded the simulation community so far. The difficulty lies in the abundance of the six-membered boroxol rings - an intermediate-range order motif suggested through Raman and NMR spectroscopy - which is challenging to obtain in atomistic molecular dynamics simulations. Here, we report the development of a DFT-accurate machine-learned potential for B$_2$O$_3$ and employ quench rates as low as 10$^{9}$ K/s to obtain B$_2$O$_3$ glasses with more than 30% of boron atoms in boroxol rings. Also, we show that the pressure, and consequently the boroxol fraction, in the deep potential molecular dynamics (DPMD) simulations critically depends on the range of the geometry descriptor used in the
embedding neural network, and at least a 9 $\unicode{x212B}$ range is required. The boroxol ring fraction increases with decreasing quench rate. Finally, amorphous B$_2$O$_3$ configurations display a minimum in energy at a boroxol fraction of 75%, intriguingly close to the experimental estimate in B$_2$O$_3$ glass.
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Medical Physics
Charge collection efficiency of thimble ionization chambers exposed to ultra-high dose per pulse
José Paz-Martín, Andreas Schüller, Marvin Apel et al. (+3 more)
Background: Commercially available ionization chambers (ICs) exposed to ultra-high dose per pulse (UHDP) exhibit deviations from a linear dose response due to volume recombination. Simulation models have been developed to describe the charge collection efficiency (CCE) but focused on parallel-plate ICs. This study aims to measure and simulate the CCE and polarity effect of thimble ICs in UHDP. Methods: The response of two PinPoint3D T31022 (PP3D) and two PinPoint T31023 (PP) ICs was investigated experimentally at the national metrology institute of Germany (PTB). The ICs were irradiated using the UHDP reference electron beam with dose per pulse up to 9.3 Gy for different voltages. A novel finite element code capable of simulating 1D and 2D geometries was developed. Results: Thimble ICs exhibit a pronounced polarization effect when irradiated with UHDP. When the sign of the collected charge is negative, the CCE is larger than when it is positive. The major contribution to the polarity effect can be attributed to the polarity-dependent charge transport and recombination. Experimental and simulated CCE (polarity effect correction factor) agrees within 1.4 % (7.0 %) and 1.6 % (3.2 %) for the PP3D and PP ICs, respectively. The CCE of parallel-plate and thimble ICs is related through a geometrical rule. Conclusions: The PP IC shows greater CCE due to its smaller external radius. The numerical model is able to satisfactory reproduce the actual CCE and polarity effect for these two chambers. At UHDP, thimble ICs should be used with caution due to their large polarity effect.
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All authors José Paz-Martín, Andreas Schüller, Marvin Apel, Araceli Gago-Arias, Juan Pardo-Montero, Faustino Gómez
Applied Physics
Compact High-Efficiency All-Polarization Rectenna for Wireless Power Transmission
Haoming He, Zongyang Dan, Zhongqi He et al. (+1 more)
In this letter, we present an innovative design for a compact, high-efficiency all-polarization receiving rectenna tailored for wireless power transmission. This rectenna, which integrates an
antenna with two same rectifier units, employs direct conjugate matching of
antenna impedance to rectifier impedance. This approach eliminates the necessity for an external impedance-matching network, thereby reducing the overall dimensions of the rectenna. The implementation of virtual ground concept streamlines the design of the rectifier's output filter. The low-profile
antenna, engineered for operation at 2.45 GHz, demonstrates high conversion efficiency across all polarization angles. The measured RF-to-DC efficiency exceeds 63% for all polarization angles, achieving a peak efficiency of 82.2%.
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All authors Haoming He, Zongyang Dan, Zhongqi He, Changjun Liu