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Physics Physics

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Thursday 27 August

Applied Physics

Hyperuniformity as a unifying organizational principle across diatom architectures

Eric Ballestero, Chiara Gazzola, Raj Kumar Pal et al. (+2 more)

Diatom frustules have long fascinated scientists for the extraordinary beauty, diversity, and functionality of their intricate silica architectures. Yet, the spatial organization of these structures has so far been primarily described in terms of morphology, symmetry, and crystallographic order, leaving common statistical properties across distinct diatom architectures largely unexplored. By analyzing diatom frustules through the lens of hyperuniformity for the first time, we reveal a striking commonality across their remarkable diversity: all analyzed genera exhibit signatures of suppressed long-wavelength density fluctuations. Specifically, we find that these architectures range from strongly ordered Class I to disordered Class III hyperuniform systems. We show that local order, spatial correlations, and long-range fluctuation suppression can vary partially independently, giving rise to a continuous spectrum of multiscale architectures. Our multiscale approach reveals that hyperuniformity can be reliably characterized in finite biological structures, beyond what conventional asymptotic diagnostics can resolve. Together, these results prove that hyperuniformity provides a unifying statistical framework for describing diatom diversity beyond conventional classifications of structural order.
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All authors Eric Ballestero, Chiara Gazzola, Raj Kumar Pal, Vicent Romero-Garc{\i}a, Marco Miniaci

Computational Physics · Cross-listed from hep-ex

Accelerating Optical Photon Simulation in DUNE with Opticks

Ilker Parmaksiz, Aaron Higuera, Laura Paulucci et al. (+2 more)

Optical photon simulation is among the most computationally demanding tasks in complex and large detector geometries. In the Deep Underground Neutrino Experiment (DUNE), the scale of the far-detector modules makes photon-by-photon transport with GEANT4 prohibitively expensive on CPUs. We present the first implementation and performance evaluation of GPU-accelerated optical photon simulation at the 10~kt scale, based on Opticks and applied to the DUNE far-detector horizontal-drift (FD-HD) geometry. On the full FD-HD geometry, Opticks propagates the same photons as GEANT4 with a speedup of $313 \pm 3$ over single-threaded and $83 \pm 1$ over four-thread GEANT4, and is validated against the reference GEANT4 simulation across all metrics considered. We further integrate Opticks into the LArSoft-based DUNE software stack. Photons simulated on the GPU with GEANT4-equivalent physics retain full Monte Carlo fidelity at a computational cost that makes high-statistics optical studies and the generation of labeled datasets for machine learning feasible at the kiloton scale.
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All authors Ilker Parmaksiz, Aaron Higuera, Laura Paulucci, Viktor Pec, Estanislao Forino

History and Philosophy of Physics · Cross-listed from hep-ph

From the November Revolution toward the Millennium

Chris Quigg

The 4th International Symposium on the History of Particle Physics spanned two decades, from approximately 1980 to 2000. In this opening keynote lecture, I survey developments in particle physics from the prehistory of the $J/\psi$ discovery to the early nineteen-eighties. I offer context for the contributions that follow in the symposium program.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci

Benchmarking of Fast and Interpretable UF Machine Learning Potentials

Pawan Prakash, Sam Dong and Richard G. Hennig

Machine learning interatomic potentials (MLIPs) have emerged as a powerful alternative to density functional theory (DFT) for molecular dynamics simulations, offering near-DFT accuracy at a fraction of the computational cost. However, many state-of-the-art MLIPs remain computationally demanding and act as black boxes, limiting physical interpretability. In this work, we evaluate the ultra-fast force field (UF$^3$) potential, which employs linear regression with cubic B-spline basis to represent effective two- and three-body interactions. We show that UF$^3$ displays accuracy comparable to established models such as GAP, MTP, NNP (Behler Parrinello), and qSNAP MLIPs. We further investigate the transferability of UF$^3$ by computing melting points for six elemental systems with potentials fitted without any solid-liquid interface configurations or explicit thermodynamic information about melting. The model reproduces experimental melting points within $\sim$6% for simple metals (Ni, Cu, Li), but substantially underestimates them for Mo and Si and fails to yield a stable potential for Ge, reflecting the limitations of a fixed expansion truncated at the three-body term for systems with strong angular or covalent bonding. We further illustrate how UF$^3$'s spline-based formulation allows direct visualization of the learned interactions, enabling identification of unphysical behavior that black-box approaches often obscure.
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Fluid Dynamics

Energy transfer and scale organisation in dense canopy turbulence

Riccardo Bertoncello, Alessandro Chiarini, Giulio Foggi Rota et al. (+2 more)

This study identifies the scale-dependent processes that sustain turbulence in dense submerged canopy flows. Using a scale-resolved energy budget, we determine where in space and at which scales production, pressure-strain redistribution, and inter-scale transfer predominantly occur, and how they link the canopy layer to the overlying shear flow. We show that energy production is localised at the interfacial shear layer, over a narrow range of streamwise and spanwise scales, while fluctuations within the canopy are primarily maintained through inter-scale transfer and pressure-strain redistribution. The dynamically active scales in the canopy are largely imposed by outer-layer structures, with their organisation and coherence mediated by these inherited motions. Energy exchange across the canopy interface is asymmetric but not unidirectional: although the dominant transfer is from the outer layer towards the canopy, intermittent reverse interactions occur at all scales. The most intense cross-interface exchanges are associated with finer-scale motions rather than large-scale structures, indicating that extreme interfacial energy fluxes are governed predominantly by small-scale dynamics. The flexibility of the canopy weakens the coherence of outer-layer structures and reduces the efficiency of inter-layer energy transfer, thereby altering both the organisation and scale of the fluctuations within the canopy. These results clarify how turbulence in dense canopies is organised and sustained, providing a unified energetic interpretation that links coherent structures to scale-dependent mechanisms.
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All authors Riccardo Bertoncello, Alessandro Chiarini, Giulio Foggi Rota, Maurizio Quadrio, Marco Edoardo Rosti

Instrumentation and Detectors

Design and performance of the Fast Beam Condition Monitor for luminosity and background measurement at the CMS Experiment in LHC Run 3

The CMS BRIL Collaboration: Eliana Acurio, Ying An, Iakov Andreev et al. (+110 more)

The Fast Beam Condition Monitor (BCM1F) has been used at the CMS Experiment since the first LHC circulating beams in 2008. Originally meant as a beam-induced background monitor for fast beam losses detection, it showed a potential also for luminosity measurements in 2012 running, and has been used for luminosity measurements since the beginning of Run 2 data taking in 2015 as a part of the Beam Radiation, Instrumentation and Luminosity (BRIL) system. Over the years, the system has undergone various upgrades to the sensors, the front-end and back-end electronics, providing improvements in the precision of the measurements, that remain valid in the higher pileup conditions of LHC Run 3 (2022-2026). Based on the experience of all BCM1F Run 2 upgrades, the detector was completely rebuilt prior to LHC Run 3 using AC-coupled silicon-pad diodes and active cooling. This latest detector version exhibits excellent linearity with instantaneous luminosity and achieves nanosecond-level timing precision, enabling improved systematic corrections for luminosity and background measurements. This paper presents a detailed overview of the detector system for LHC Run 3, including the selection and qualification of sensors as well as a summary of the readout system. It also outlines the processing and calibration strategy for luminosity data, discussing operational hurdles and comparing BCM1F measurements to other CMS luminosity measurements to assess the system's performance as a luminometer. Lastly, the implications for the design of a future luminosity detector to be used in the envisioned HL-LHC upgrade are discussed.
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All authors The CMS BRIL Collaboration: Eliana Acurio, Ying An, Iakov Andreev, Tomas Atehortua, Georg Auzinger, Hamed Bakhshiansohi, Gergely Balint, Luis Ignacio Banos, Juan Pedro Barajas Ibarria, Hugo Alberto Becerril, Jose Feliciano Benitez, Philip H. Butler, Alan Campbell, Edgar Fernando Carrera Jarr{\i}n, Alfredo Castaneda Hernandez, Marco Costa, Antonio Cota Rodriguez, Luis Enrique Cuevas Picos, Anne Dabrowski, Vladyslav Danilov, Andres Guillermo Delannoy Sotomayor, Hedwin Aaron Encinas Acosta, Krisztian Farkas, Anna Feherkuti, Mahmoud Moussa Abdelkhalek Gadallah, Luis Gabriel Gallegos Marinez, Angela Giraldi, Alfredo Gurrola, Moritz Guthoff, Mykyta Haranko, Maria Hempel, Hans Henschel, Shilpi Jain, Armin Kadlecsik, Jan Kaplon, Adam Kardos, Olena Karacheban, Nimmitha Karunarathna, Joscha Ahauser, Georgios Krintiras, Leen Lambers, Jessica Leonard, Moises David Leon Coello, Maksim Jenihhin, Willard Johns, Markus Klute, Wolfgang Lange, Kuan-Yu Lin, Wei Heng Liu, Wolfgang Lohnmann, Arkady Lokhovitskiy, Robert Loos, Peter Major, Sophie Mallows, Jeremiah Mans, Daniel Marlow, Badder Marzocchi, John-Erik Meißner, Philip Jason Meltzer, Stefano Mersi, Andreas Bernhard Meyer, Dmitri Mihhailov, Valeria Monti, Michele Mormile, Javier Alberto Murillo Quijada, Vlodymyr Myronenko, Cristina Oropeza Barrera, Younes Otarid, Christopher Palmer, Jose David Ochoa Flores, Michelangelo Pari, Gabriella Pasztor, Marek Penno, Fabio Lucas Pereira Carneiro, Elena Popova, Attila Jozsef Radl, Evan Altair Ranken, Beatriz Ribeiro-Lopes, Francesco Romeo, Carlos Romero, Jonas Rubenach, Alexander Ruede, Vladimir Ryjov, Santeri Saariokari, Alessia Saggio, Valerie Scheurer, Vahid Sedighzadeh Dalavi, Mohammad Sedghi, Tatiana Selezneva, Konstantin Sharko, Alexey Shevelev, Konstantin Shibin, Sunil Somalwar, Rafael Sosa, Stefan Spanier, David Stickland, Robert Stone, Andromachi Tsirou, Oleksii Turkot, Lizardo Valencia Palomo, Cristina Vazquez Velez, Roger Rusack, Paola Tropea, Balazs Ujvari, Mayda Velasco, Piero Giorgio Verdini, David Walter, Joanna Wanczyk, Jesus Alberto Velazquez Corral, Daniel John Wilbern, Zhen Xie, Maryam Zeinali, Wolfram Zeuner

Atomic Physics

Influence of Many-Body Dipole-Dipole Interactions on Excitation Transfer in a Dense Gas

A. A. Bobrov, S. A. Saakyan, B. B. Zelener et al. (+1 more)

We study non-radiative dipole-dipole induced excitation transfer in dense Rb vapour. We show that density dependence of characteristic time of the excitation diffusion changes from linear to non-linear for high Rb density. It is attributed to the breakdown of binary collisions approach to the dipole-dipole excitation transfer. It is shown that the observed result can be qualitatively described if the mean free path is replaced by mean interatomic distance for the chracteristic diffusion length.
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All authors A. A. Bobrov, S. A. Saakyan, B. B. Zelener, V. A. Sautenkov

Accelerator Physics

Large Magnet Structures for Fusion Technology: Lessons from ITER

Neil Mitchell

Over a period of 40 years, the ITER project has provided many examples in large magnet structures, from pre-concept to design to manufacture to delivery and assembly, from which lessons can be learned for the future. This presentation is divided into three parts. The first, 'Making and Assembling Large (steel) Cryogenic Structures for Magnets' is based on ITER Coil Structure experience, particularly the Central Solenoid (CS) and Toroidal Field (TF) structures and particularly on large 316LN forgings weighing about 50t individually, requiring then high accuracy machining and deep (up to 0.3m) welds with controlled distortion. New materials development is often proposed. This is easy on a laboratory scale, but often not transferable to an industrial large scale. Examples are provided. The issues to be considered (and solved) are large scale quality (and repair of defects), joining, tolerances and assembly. The second 'Designing Large Steel Support Structures for Magnets' is concerned with structural design codes & criteria, and modern analysis, especially of imperfect, but manufacturable structures. Points that are considered are typical critical issues with cyclically loaded thick components, analysis of partial penetration welds and other welds not permitted under normal American Society of Mechanical Engineers (ASME) welding procedures (including fillet welds and/or those volumetrically not inspectable by Non-Destructive Examinations (NDE)) and allowing for tolerance compensation (i.e. designing with overmetal or designing for shimming). The third 'Avoiding or Reducing Large Steel Support Structures for Magnets' shows how it is possible to choose other routes to include structural materials in magnets, for example (as in ITER TF coils) by using plates to contain the conductor, or by using a thick conductor jacket to at least share the loads with massive steel cases.
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Medical Physics

Constrained estimation of rotational invariants of the cumulant expansion (RICE) for rapid tensor-valued diffusion MRI

Jinyang Yu, Oliver Gödicke, Frederik B. Laun et al. (+10 more)

Purpose: To complement 1.5-minute measurements of common tensor-valued diffusion MRI (dMRI) markers with rapid constrained fitting. Methods: Fast dMRI protocols for obtaining rotational invariants of the cumulant expansion (RICE) were paired with constrained weighted linear least squares (CWLLS) to stabilize the more fragile WLLS fit. A compact constraint set was formulated, including a novel mean-dependent upper bound on total diffusional variance. Evaluation used diffusion tensor distribution (DTD) simulations, healthy-volunteer data with a resolution-dependent SNR experiment, and a glioma patient dataset. A 5-minute q-space trajectory imaging (QTI) protocol served as a reference. Results: Across experiments, CWLLS reduced unphysical estimates and fit outliers in parameters such as microscopic FA and isotropic diffusivity variance. In simulations, it narrowed error distributions most clearly in the CSF-dominant case, while some metrics showed a bias-variance trade-off. In vivo, CWLLS removed negative variance estimates, truncated out-of-bounds tails, and reduced artifacts in fluid-contaminated voxels while preserving anatomical contrast. It also retained more stable maps than WLLS at higher resolution, although both estimators degraded in the lowest-SNR setting. Notably, the new mean-dependent variance bound was violated in 15.4% of voxels in the patient dataset, accounting for nearly half of the 32.7% that violated at least one constraint. Healthy-volunteer benchmarking showed that CWLLS completed in under 30 seconds. The constrained QTI fit required 72 minutes, making CWLLS 160 times faster. Conclusion: CWLLS for fast RICE yielded high-quality parameter maps at an online-ready computational cost. This may enhance the reliability of dMRI tissue characterization and strengthen the path toward clinical translation.
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All authors Jinyang Yu, Oliver Gödicke, Frederik B. Laun, Obada T. Alhalabi, Iris A. Kohler, Jürgen Hesser, Sandro M. Krieg, Bogdana Suchorska, Heinz-Peter Schlemmer, Mark E. Ladd, David Bonekamp, Johann M. E. Jende, Tristan A. Kuder

Physics and Society

Distinct routes to phase transitions in spatial activation systems

Jialu Zhang, Guanyu Zhang, Leyang Xue et al. (+1 more)

Threshold-driven activation governs a wide range of collective phenomena, yet the microscopic origins of its phase transitions in spatial systems remain unresolved. Here, we show that spatial activation systems undergo multiple distinct routes to phase transitions, controlled by a single parameter—the interaction range. We uncover a unified phase diagram featuring continuous, first-order, and mixed-order transitions, and demonstrate that the two abrupt transitions arise from fundamentally different mechanisms: nucleation-driven front propagation and critical branching. These routes exhibit distinct dynamical scaling, establishing a direct link between microscopic activation dynamics and macroscopic critical behavior. We further identify a metastable phase in which global activation cannot be achieved by random activation alone, but can be triggered by localized seeds. In this regime, the critical activation nucleus remains finite and independent of system size, implying that arbitrarily large systems can remain stable under random perturbations yet highly vulnerable to localized triggers. The onset of this phase is abrupt, revealing an extreme sensitivity of collective dynamics to small parameter changes. These results establish a mechanistic framework for phase transitions in spatial activation systems and reveal how microscopic perturbations can trigger macroscopic cascades.
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All authors Jialu Zhang, Guanyu Zhang, Leyang Xue, Peng-Bi Cui

Chemical Physics

ElemCo.jl: A Julia package for electron-correlation methods

Daniel Kats, Charlotte Rickert, Thomas Schraivogel et al. (+3 more)

We present ElemCo.jl, an open-source Julia package for molecular electronic structure and properties calculations with a particular emphasis on Coupled Cluster and Distinguishable Cluster methods. The package provides a high-level, macro-based user interface which makes routine calculations accessible to users with no prior Julia experience. A newly developed visualizer, JLmol, assists in the graphical preparation of ElemCo.jl input files and displays results such as molecular orbitals. ElemCo.jl offers restricted closed-shell and unrestricted variants of state-of-the-art electron-correlation methods such as FCI, MP2, CCSD(T) as well as EOM-CCSD and the DC methods DCSD and DC-CCSDT. In addition to traditional approaches, ElemCo.jl provides recently developed methods that are currently unique to the package. These include tensor-decomposed implementations of DCSD and DC-CCSDT (SVD-DCSD and SVD-DC-CCSDT) as well as two-determinant and fixed-reference CC and DC methods. For excited-state calculations, ElemCo.jl also offers EOM-DCSD, which is benchmarked in this work against CC3 on the QUEST3 benchmark set, alongside EOM-CCSD. Furthermore, both ground and excited states, including those of multireference character, can be treated using CIPHI - an efficient selected Configuration Interaction (CI) approach employing a CIPSI/Heat-Bath-CI-based algorithm. Users can directly invoke internal functions from the input file, enabling them to test and compose new methods without the need to modify ElemCo.jl's source code. Also, ElemCo.jl can be readily interfaced with external quantum chemistry codes through the Fcidump format, for example as the high-level solver for transcorrelated Hamiltonians, periodic embedded fragments, etc. We provide a detailed overview of ElemCo.jl's methodological repertoire and discuss its technical details and implementation, performance, interfaces, and usage.
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All authors Daniel Kats, Charlotte Rickert, Thomas Schraivogel, Kristoffer Simula, Denis Usvyat, Fangcheng Wu

Applied Physics

Diamond quantum-sensing platform with integrated boron-doped diamond microwave antenna and thermometer

Masahiro Ohkuma, Ryo Matsumoto, Shintaro Adachi et al. (+5 more)

Wide-field nitrogen-vacancy (NV) magnetic imaging at cryogenic temperatures requires microwave excitation and reliable knowledge of the temperature near the sensing region. Here, we report an integrated diamond quantum-sensing platform combining an ensemble of NV centers with a boron-doped diamond (BDD) microwave antenna and thermometer formed on the same diamond substrate. The BDD antenna provides microwave excitation for optically detected magnetic resonance measurements, and the BDD thermometer monitors the thermal environment near the NV sensing region. The BDD thermometer detected laser-induced local heating that was not clearly resolved by a stage-mounted thermometer. Using this platform, we imaged the temperature-dependent Meissner response of multiple cuprate superconductors while recording the temperature. These results demonstrate that the integrated BDD–NV platform provides a practical approach for cryogenic wide-field magnetic imaging with integrated microwave delivery and local thermometry.
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All authors Masahiro Ohkuma, Ryo Matsumoto, Shintaro Adachi, Shinobu Onoda, Kensei Terashima, Takao Watanabe, Yoshihiko Takano, Keigo Arai

Chemical Physics

Franson-Interferometric Bounds on Entangled Two-Photon Absorption

Albin Hedse, Sankaran Ramesh, Luis Matheis et al. (+7 more)

Entangled photons offer quantum correlations with no classical analogue. In entangled pair two-photon absorption (ETPA), absorption rate is predicted to scale linearly rather than quadratically with photon flux, promising molecular excitation at fluxes far below the classical threshold. Reported ETPA cross sections nevertheless vary widely across experiments, largely since the observable, the differential of the transmitted flux or weak fluorescence, is difficult to separate from scattering and linear losses. We present a method which uses Franson interference to study entangled two-photon absorption through delay-dependent coincidence measurements on dye molecules. Applying the method to Rhodamine 6G, we observe a small asymmetry in the Franson interference envelope and obtain a model-derived effective cross section of approximately 2.1 E(-21) centimeter squared for Rhodamine 6G. However, the estimated systematic uncertainty does not allow a definitive ETPA assignment. Instead, the experiment establishes a quantitative bound on the ETPA response and provides a background-free benchmark for future measurements.
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All authors Albin Hedse, Sankaran Ramesh, Luis Matheis, Sebastian Gstir, Andreas Wacker, Gregor Weihs, Robert Keil, Qi Shi, Amitav Sahu, Tõnu Pullerits

Geophysics

Quantifying the effects of nickel on Earth's inner-core nucleation

Jiahui Zhai, Liangrui Wei, Chen Gao et al. (+1 more)

The formation of Earth's solid inner core marks a major transition in the thermal and chemical evolution of the deep Earth, yet its origin remains paradoxical, as initial nucleation appears to require unrealistically large undercooling in the outer core. Here, we use atomistic simulations to quantify how Ni affects this process under inner-core conditions. While Fe-Ni alloys preserve strong thermodynamic competition between the hcp and bcc phases, the bcc phase consistently forms smaller critical nuclei and has lower nucleation barriers than hcp. Increasing Ni content in the melts further lowers the nucleation barrier and shortens the nucleation waiting time. Local chemical fluctuations also strongly affect the macroscopic nucleation rate. Combining these effects, bcc nucleation in Fe80Ni20 reaches about 250 K of undercooling, approaching geophysical constraints. We demonstrate that Ni enrichment, bcc nucleation, and chemical heterogeneity substantially narrow the inner-core nucleation paradox.
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All authors Jiahui Zhai, Liangrui Wei, Chen Gao, Yang Sun

Space Physics · Cross-listed from astro-ph.EP

Narrow-Shell Stochasticity in Source-Sink Models of the Low Earth Orbit Environment

Jaewon Choi, Souvik Dhara and Harsha Honnappa

Deterministic source-sink models are widely used to assess the long-term evolution, capacity, and sustainability of the low Earth orbit (LEO) environment. These models propagate shell-averaged populations through ordinary differential equations (ODEs), relying on individual collision, disposal, and decay events to average out within sufficiently large altitude shells. As constellation traffic is increasingly organized into kilometer- and sub-kilometer-scale shells, this averaging assumption becomes strained. We formulate the multi-shell, multi-species LEO environment as a Markov jump process and, from this formulation, recover the conventional source-sink ODE as a large-volume limit and derive a stochastic differential equation (SDE) approximation whose fluctuations scale as V^{-1/2} in the per-shell volume V. The diffusion approximation is validated against an exact discrete-event simulation of the underlying jump process. Sweeping V at fixed spatial density over the 450-800 km band, we find that the two descriptions agree at shell volumes comparable to those used in established source-sink models but diverge as shells narrow. At the finest shell volume considered, the mean debris population reaches roughly 4.5 times the ODE prediction, with several realizations undergoing runaway growth absent from the ODE trajectory. This departure is driven by nonlinear collision terms, through which population variance and covariance raise expected collision rates, generating further debris and reinforcing the collision-debris feedback. Narrow-shell stochasticity thus both widens the outcome distribution and shifts the expected trajectory. Because the stochastic model shares its parameterization with the deterministic one, it provides a scale-consistent extension of existing source-sink models for evaluating shell configuration, collision risk, and long-term LEO sustainability.
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Applied Physics

Diatom frustules as naturally occurring resonant microarchitectures: revealing vibrational eigenmodes across pennate and centric species

Chiara Gazzola, Dame Fall, Stefano Stassi et al. (+3 more)

Diatom frustules, the hierarchically structured, species-specific silica exoskeletons of diatom microalgae, are among Nature's most sophisticated examples of bottom-up self-assembly, exhibiting nanoscale porosity, multifunctional mechanical and optical properties, and a morphological diversity that spans nearly three orders of magnitude in size. Despite growing interest in their optical and static mechanical properties, the elastodynamic behaviour of frustules has remained largely unexplored. Here we report the first experimental detection and spatially resolved reconstruction of vibrational eigenmodes in diatom frustules, combining laser Doppler vibrometry with morphology-faithful finite-element models informed by scanning electron microscopy (SEM) and focused-ion-beam scanning electron microscopy (FIB-SEM). Two morphologically contrasting taxa were investigated as model systems: the pennate diatom Rhaphoneis amphiceros and the centric diatom Stictodiscus californicus var. nitida, spanning the two principal branches of diatom diversity. Four eigenmodes were identified for R. amphiceros in the 5.90-14.17 MHz range and three for S. californicus in the 9.96-17.62 MHz range; the simulations yield a complete modal landscape for each species, including modally split and nearly degenerate eigenmodes arising from deviations from ideal symmetry, and show quantitative agreement with the experimentally measured mode shapes and resonant frequencies. These results establish diatom frustules as a class of naturally occurring resonant microarchitectures, and open new avenues for their integration as bio-derived functional elements in nanomechanical and MEMS/NEMS applications.
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All authors Chiara Gazzola, Dame Fall, Stefano Stassi, Marc Duquennoy, Marc Serra Garcia, Marco Miniaci

Chemical Physics · Cross-listed from quant-ph

Kramers pseudospin and the quantum number proposed for the many-electron Dirac?Coulomb Hamiltonian

Shadan Ghassemi Tabrizi

The square of a sum of single-electron time reversals has been proposed as a conserved quantity with an integer eigenvalue spectrum for the many-electron Dirac-Coulomb Hamiltonian [Phys. Rev. A 94, 052104 (2016)], and its expectation value is in use as a diagnostic of Kramers contamination. This work identifies the operator behind the construction, a component of a pseudospin attached to the chosen Kramers pairs, whose angular-momentum algebra reproduces the reported spectrum and yields the eigenvectors in closed form. The label $k$ entering the proposed quantum number $-k^2$ is twice the magnitude of a pseudospin projection onto an axis fixed by the basis and changes when the Kramers pairs are rephased. The commutation with the Hamiltonian is unfounded, and the proposed quantum number does not stand.
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Fluid Dynamics

Stochastic Transport and Wave Interactions for Multiscale Surface Gravity Waves: Part II: Kinetic Theory and Ocean-Wave Applications

E. Mémin, B. Chapron, A. Debussche et al. (+1 more)

Building on the stochastic variational framework established in the companion paper, we investigate here the linearized stochastic water-wave system, consisting of a large-scale stochastic wave dynamics coupled to transport dynamics for the small-scale correlation modes. Within this framework, we develop, in the deep-water regime, a kinetic theory for surface gravity waves interacting with unresolved stochastic velocity fields. An energy analysis yields a wave-action kinetic equation exhibiting two distinct regimes: a diffusive scattering regime and a quartic interaction regime with structural similarities to Hasselmann–Zakharov theory. In the present framework, these effective quartic interactions arise through stochastic transport of unresolved fluctuations by the large-scale flow rather than through classical intrinsic resonant nonlinearity. Scaling laws are derived for the diffusion tensor and the effective growth rate, revealing a Miles-type production–dissipation mechanism. Using JONSWAP spectra, we then compare the strength of stochastic transport and classical Hasselmann interactions. For realistic oceanic values of unresolved velocity variance ($\sigma_u \approx 0.1\,\mathrm{m\,s^{-1}}$) and decorrelation time ($\tau_c \approx 10\,\mathrm{s}$), stochastic transport is found to compete with, and often exceed, classical four-wave interaction rates over broad spectral ranges. The transport intensity $S=\sigma_u^2\tau_c$ emerges as a key parameter controlling the transition between interaction regimes. These results suggest that unresolved stochastic transport may play a substantially larger role in spectral evolution than is commonly represented in operational wave models, and motivate the inclusion of transport-induced source terms alongside standard resonant interaction closures.
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All authors E. Mémin, B. Chapron, A. Debussche, L Marié

Atomic Physics

Beyond-EUV spectrum of highly-charged gadolinium

M.L. Reitsma, J. Sheil, O.O. Versolato et al. (+2 more)

We report ab initio relativistic calculations on the complex Gd$^{18+}$ and Gd$^{26+}$ highly-charged ions, which are relevant to beyond-extreme-ultraviolet (BEUV) light sources based on laser-produced gadolinium plasmas. Using the particle-hole configuration-interaction with many-body perturbation theory (CI+MBPT) method, we systematically saturate the $n=4$ configuration space and determine the influence of multiply excited states on the emissivity spectrum. For Gd$^{26+}$ we find behavior analogous to that of its isoelectronic counterpart Sn$^{12+}$, with strong contributions from multiply excited states, where even the quadruply excited states become significant at certain effective temperatures. In contrast, the industry-relevant 6.7 nm emission of Pd-like Gd$^{18+}$ is dominated by the singly excited $4d^{10} {\ }^{1}S_{0}$ – $4d^{9}4f {\ }^{1}P_{1}$ transition, while multiply excited states primarily contribute to out-of-band emission. The calculated spectra show good agreement with experiment and demonstrate that the importance of multiply excited states depends strongly on both charge state and plasma conditions.
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All authors M.L. Reitsma, J. Sheil, O.O. Versolato, E.V. Kahl, J.C. Berengut

Atmospheric and Oceanic Physics · Cross-listed from math-ph

Coupled stochastic variational principles for multiscale surface gravity waves – Part I: theoretical framework

Etienne Mémin and Arnaud Debussche

This paper develops a comprehensive stochastic variational framework for surface gravity waves. Starting from Luke's variational principle for irrotational, incompressible free-surface flow, we introduce a decomposition of the velocity potential into a large-scale deterministic component and a regularized stochastic noise term representing unresolved scales. A path-wise variational principle yields the stochastic counterparts of the Laplace, Bernoulli, and kinematic boundary conditions. To close the system, a second variational principle in expectation is formulated, providing evolution equations for the noise correlation functions. The resulting coupled system preserves the Hamiltonian structure of the Zakharov–Craig–Sulem formulation. We further analyze explicit solutions via WKB approximation and show that the noise correlation functions satisfy a Hamilton-Jacobi equation with ray-tracing dynamics. This framework provides a rigorous foundation for reduced stochastic models of ocean waves and for the kinetic theory developed in the companion paper.
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Applied Physics

Ternary-Valued Finite-Difference Time-Domain Method: Asymptotic Agreement with the Yee Scheme Through Noise-Shaped Quantisation

Ivan S. Maksymov

I show that finite-difference time-domain (FDTD) dynamics can be reproduced using field variables restricted to the ternary alphabet ${-1,0,+1}$. The integration is carried out by a state accumulator, while quantisation is done by a second-order noise-shaped encoder with a separate error register. The Courant number $S$ plays two roles: it is the exact fixed-point ratio and also sets the encoder's oversampling ratio. When $S$ is chosen as a power of two, each cell update requires neither run-time multiplication nor floating-point arithmetic, and each emitted field symbol is represented by just two bits. The ternary scheme converges asymptotically to the standard Yee scheme as $S$ decreases towards zero. I report wall-clock and instruction counts relative to a floating-point reference, long-time energy integrations over $2\times10^{5}$ steps and the $S$ required to achieve a prescribed accuracy for the driven mode. Extending the approach to acoustics, Virieux-type elastodynamics and Schrodinger-equation solvers is a prospective direction towards a broader class of quantised physics solvers for resource-constrained and specialised hardware.
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Optics

Self-starting Dynamics in All-fibre All-Normal-Dispersion Thulium Mamyshev oscillator

Dennis C. Kirsch, Kirill Grebnev, Alberto Rodriguez Cuevas et al. (+8 more)

Ultrashort pulse formation from noise represents a fundamental self-organisation process in nonlinear dissipative systems and remains central to ultrafast photonics. Mamyshev oscillators offer a particularly valuable platform for investigating this phenomenon because they do not rely on conventional saturable absorbers. Instead, pulse formation is governed by self-phase modulation in normal-dispersion fibres combined with periodic offset spectral filtering. Achieving self-starting pulse formation in these systems is challenging, particularly at longer wavelengths, due to limited normal-dispersion components and the complex gain dynamics. This work reports, to the best of current knowledge, the first self-starting, all-fibre, all-normal-dispersion Thulium-doped Mamyshev oscillator operating near 1.9um. The cavity employs a compact Fabry-Perot design incorporating a dispersion-engineered Thulium-doped gain fibre, a highly nonlinear passive normal-dispersion fibre, and a pair of chirp-free broadband fibre Bragg gratings. The oscillator self-starts without external seeding or active modulation and stabilises noise-like pulse generation regime at a fundamental cavity repetition rate. Real-time measurements and numerical simulations reveal the build-up pathway from noise through transient multi-pulsing and pulse competition to a stationary noise-like envelope. Our results show that both tailored laser components and gain-medium-specific dynamics are essential for enabling self-starting ultrashort pulse generation in Mamyshev oscillators and for extending these laser concepts beyond the near-infrared, thereby facilitating the development of compact and robust shortwave infrared (SWIR) sources and new regimes of ultrafast self-organisation.
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All authors Dennis C. Kirsch, Kirill Grebnev, Alberto Rodriguez Cuevas, Mikhail E. Likhachev, Svetlana S. Aleshkina, M. V. Yashkov, Sonja Unger, Claudia Aichele, Adrian Lorenz, Auro Perego, Maria Chernysheva

Fluid Dynamics

High-resolution in situ analysis of biomass pyrolysis by combining quantitative synchrotron $\mu$CT and 3D particle-resolved simulations

Emeric Boigné, Mohamed M. Ahmed, Collin Foster et al. (+7 more)

Understanding the coupling between transport, chemical kinetics, and structural response within solid fuel combustion requires in situ measurements at high spatial resolution. To examine the dynamics of biomass pyrolysis, we optimize synchrotron X-ray micro-computed tomography ($\mu$CT), and conduct 3D particle-resolved simulations. A micro-focused heating cell with controlled heating and flow rate is employed, achieving temperatures of up to 1240 K and 3D imaging at 3.24 $\mu$m spatial and sub-minute temporal resolutions. The pyrolysis of three biomass materials at sample heating rates of 10-14 K/min are examined. The $\mu$CT measurements capture pore deformation, cracking, anisotropic shrinkage, and provide simultaneous thermogravimetric and thermovolumetric analyses to examine specific secondary pyrolysis pathways. Complementary 3D simulations considering detailed kinetics and structural response reproduce the key trends observed, and identify deficiencies in capturing simultaneous mass and volume losses during pyrolysis.
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All authors Emeric Boigné, Mohamed M. Ahmed, Collin Foster, Edna R. Toro, Dilworth Y. Parkinson, Alastair A. MacDowell, Harold S. Barnard, Francesco Panerai, Chiara Saggese, Matthias Ihme

Optics

Field-driven attosecond deflection of electron beams at the position of planar foils

Xiaofan Gui, Kenichi L. Ishikawa and Yuya Morimoto

While the coupling of free-electron beams and light has enabled the control of electron's quantum states and the generation of ultrashort electron pulses, it can distort the measured signal when probing a laser-driven sample with an electron beam. Here, we theoretically study optical-field-driven beam deflection that inevitably occurs at the location of a laser-excited sample. Treating electrons in a beam as classical point particles and focusing on thin planar samples, we conduct a systematic study of the instantaneous deflection amplitudes with respect to light polarization, material type, thickness, and interaction geometry. For s-polarized excitation fields, the deflection amplitude is strictly proportional to the excitation-field amplitude in a foil, making beam deflection unavoidable. Conversely, for p-polarized fields, a nontrivial relationship emerges between the deflection amplitude and the field amplitude due to the interplay of electric and magnetic fields coupled with the electron-light velocity mismatch. Crucially, we demonstrate that the deflection can be minimized even under high field strengths by selecting an optimal configuration for a given foil material and thickness. These findings provide key guidelines for designing future time-resolved imaging experiments using ultrashort electron beams.
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Applied Physics · Cross-listed from cond-mat.mes-hall

Magnon-induced phononic Chern insulator

Rui-Chang Shen, Yihao Yang and Haoran Xue

High-frequency artificial phononic crystals offer a low-loss platform compatible with on-chip integration, yet realizing Chern phononic phases at GHz frequencies remains challenging. Here, we propose a magnon-induced phononic Chern insulator in a honeycomb phononic crystal hybridized with ferromagnetic islands at the hexagon centers. A circularly polarized Kittel mode couples to the surrounding phonons with a phase winding, which breaks time-reversal symmetry and opens a full Chern gap. In the large-detuning regime, this mechanism leads to an effective Haldane-type phononic model with magnon-induced complex hopping. By tuning the magnon-phonon interaction, the full hybrid system accesses Chern phases with tunable Chern numbers |C|=1 and |C|=2. The predicted gaps can exceed realistic phonon and magnon linewidths, enabling their observation in GHz acoustic devices. Our work establishes chiral magnon–phonon hybridization as a route to magnetically reconfigurable topological phononics.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci

Topology-Controlled Phonon Dielectric Response Beyond Density Scaling in Metal-Organic Frameworks

Debayan Mondal, Jiahao Ye, Lorenzo Donà et al. (+1 more)

Effective-medium theory treats material porosity as passive dilution. Using ab initio density functional theory and high-resolution synchrotron terahertz (THz) spectroscopy on isochemical zeolitic-imidazolate frameworks, we show that while the electronic permittivity obeys Clausius-Mossotti density scaling, the phonon contribution violates the conventional density scaling rules. Identical Born charges rule out the role of local chemistry. Instead, the framework connectivity localizes the THz response, where the coherency of phonon eigenvectors determines the mode-effective charges. Long-range architecture of framework topology ubiquitous in metal-organic frameworks is therefore a dielectric degree of freedom beyond the density scaling of conventional solids.
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All authors Debayan Mondal, Jiahao Ye, Lorenzo Donà, Jin-Chong Tan

Fluid Dynamics

Quantum-Inspired Computational Fluid Dynamics for Transient Turbulent Compressible Flows

Shang Xian Matthew Lee, Melissa Kozul, Muhammad Usman et al. (+3 more)

Quantum-inspired algorithms are an emerging class of algorithms for computational fluid dynamics (CFD) with potentially favourable scaling for large problems compared to classical methods. However, their applications have been limited to incompressible flows due to arithmetic limitations, which are addressed in this work. This work introduces the first true end-to-end quantum-inspired computational fluid dynamics (QICFD) solver for direct numerical simulation of the compressible Navier-Stokes equations, that is, all arithmetic operations, as well as initialisation and post-processing, are undertaken in the tensor train (TT) format. Importantly, new division and square-root algorithms using TTs enable the use of Sutherland's law for viscosity, and leverages recent improvements in TT arithmetic algorithms for reduced runtime and memory cost. The new QICFD solver is validated by comparison with the classical CFD solver HiPSTAR and by way of a challenging fluid-flow test case, the low resolution Taylor-Green Vortex (TGV) at Mach numbers of 0.8 and 0.1. The TGV test case is a transient turbulent case that is very sensitive to accumulating errors, yet our QICFD solver achieves excellent agreement with the classical CFD reference. This work demonstrates the correctness of the new TT division and square-root algorithms, and that QICFD is capable of compressible flow simulations. The new QICFD solver is also able to perform simultaneous simulations, running multiple TGV-like cases initialised differently in parallel with reduced extra cost. Finally, the demonstrated TGV test case reveals additional challenges of QICFD as well as highlight the need for future advances to make TT methods viable for industrially-relevant conditions.
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All authors Shang Xian Matthew Lee, Melissa Kozul, Muhammad Usman, Martin Sevior, Matthew L. Sims-Goh, Richard D. Sandberg

Optics

Cavity Solitons

W.J. Firth and G.K. Harkness

A driven optical cavity containing a nonlinear medium can support stable, soliton-like objects, bright non-diffracting spots of light on a uniform background. Importantly, the nonlinear medium need not support ordinary (propagating) spatial solitons, and cavity solitons have been both predicted and observed in a saturable absorber, and predicted to even exist in self-defocusing media. The history, present status, and physical interpretation of such cavity solitons is reviewed. Recent research predicts cavity solitons in semiconductor cavity models with properties interesting for applications to optical information processing. Cavity solitons are natural `bits' for spatial information, possessing both robustness and plasticity, and some potential applications of their unique properties are mentioned.
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Fluid Dynamics

Turbulent diffusivity and effective rise velocity of buoyant particles in a free-surface boundary layer

Julio E. Chávez-Dorado, Lucia J. Baker, James J. Riley et al. (+1 more)

Predicting the transport of buoyant particles in a free-surface boundary layer is important to the study of many environmental systems, including microplastics in the upper ocean. Current transport models, adapted from sediment transport theory, typically rely on assumptions of a quiescent rise velocity and gradient diffusion with an uncertain turbulent Schmidt number $Sc_t$. Here, we test this type of model against experiments by studying the vertical mixing of near-neutrally buoyant, finite-size spheres, rods, and disks in a wind-driven, wavy free-surface flow. We measure particle diffusivity directly from Lagrangian trajectories and compare against Eulerian concentration-based estimates. Overall, we find that particle buoyancy is the main control on the diffusivity, and that the diffusivity decreases as particle rise velocity grows relative to the turbulent fluctuations. These observations we find to be consistent with the crossing-trajectories theory, even in the presence of waves. In addition, we find that inferring the diffusivity from concentration profiles with an assumed quiescent rise velocity overestimates the diffusivity by up to a factor of $5$, consistent with effective rise velocities up to $80\%$ lower than the corresponding quiescent values. We also directly measure $Sc_t \approx 1$ for the neutrally-buoyant particles and $Sc_t > 1$ for the buoyant particles. Together, these experimental results demonstrate how standard model closures may be biased in both their diffusivities and rise velocities when applied to buoyant particles at the ocean surface.
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All authors Julio E. Chávez-Dorado, Lucia J. Baker, James J. Riley, Michelle H. DiBenedetto

Applied Physics · Cross-listed from quant-ph

Isotropic Nanoscale Quantum Sensor at Room-Temperature

Daniel T. Möller, Baha Sakar, Ekrem T. Güldeste et al. (+9 more)

Color-center based quantum sensors provide nanoscale resolution under ambient conditions, yet their applicability remains limited. Because the quantization axes are locked to the host lattice, conventional color centers suffer severe signal loss in off-axis magnetic fields. To address this, we report an isotropic magnetometer enabled by the neutrally charged nitrogen-vacancy center (NV0) in diamond. Here, spin-to-charge dynamics yield an NV0-dark spin pair whose quantization axis dynamically aligns with the external field. Read out through NV charge-state-selective fluorescence, this system exhibits microsecond room-temperature coherence and nanotesla sensitivity for arbitrary field directions. We demonstrate alignment-free mapping of steep field gradients and single paramagnetic micro-targets, alongside isotropic readout from randomly oriented nanodiamonds. Resolving longstanding orientation constraints, this platform unlocks unrestricted nanoscale magnetometry across life sciences and quantum materials.
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All authors Daniel T. Möller, Baha Sakar, Ekrem T. Güldeste, Dhruv Wadhwani, Olt Gashi, Daniel A. García Vaca, Mokessh K. Ciwan, Simone P. Crozier, Christian Laube, Sirswa K. Shree Ram, Matteo Slaviero, Nabeel Aslam