Physics and Society
Strongly clustered random graphs via triadic closure: Degree correlations and clustering spectrum
Lorenzo Cirigliano, Gareth J. Baxter and Gábor Timár
Real-world networks often exhibit strong transitivity with nontrivial local clustering spectra and degree correlations. Such features are not easily modeled in tractable network models, creating an obstacle to the theoretical understanding of such complex network structures. Here, we address this problem using a model for strongly clustered random graphs in which each triad of a random network backbone is closed with a certain probability. Despite the intricate loopy local structure of the graphs obtained, we provide exact expressions for the local clustering spectrum and the degree correlations, filling the gap in the theoretical description of this model for random graphs. In particular, we find positive degree assortativity accompanying high transitivity, and nontrivial structure in the clustering spectrum. Exact asymptotic analytical results, obtained for uncorrelated locally tree-like backbones, are complemented with extensive numerical characterization of finite-size effects.
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Atomic Physics · Cross-listed from quant-ph
Photon statistics in waveguide QED: II Exact solutions in a thermodynamic limit
M. Eltohfa and F. Robicheaux
Waveguide
quantum electrodynamics (WQED) offers a powerful framework for controlling light-matter interactions and realizing collective phenomena such as super- and subradiance. In general waveguide settings, the
quantum dynamics spans the full
Hilbert space, rendering exact theoretical treatments exponentially difficult and currently out of reach, and only a few models have exact, analytical solutions. Motivated by recent experiments, we treat the thermodynamic limit of the number of atoms, $N \rightarrow \infty$, while the homogeneous atom-waveguide coupling $\beta \rightarrow 0$ keeping the optical depth $4N\beta$ fixed. In this limit, a second order mean field method is exact, giving analytical solutions for the statistics of the
photons emitted in the waveguide both for
chiral and symmetric configurations starting from full inversion. As $N \rightarrow \infty$, the emission in freespace approaches that of an independent ensemble. However, until a special time, $\approx 1.59 \times$ the lifetime of a single-atom, we show an exponentially enhanced superradiance in the waveguide as the optical depth increases. After the special time, the emission into the waveguide exhibits subradiance. We also show that the initial shot-to-shot fluctuations in the rate of emission into the waveguide diminish in a
chiral system and vanish in a symmetric system as $N$ approaches $\infty$. Additionally, the equal-time second-order correlation becomes trivial, showing that finite-size effects are essential to observe the emergence of second-order coherence. Finally, going beyond the thermodynamic limit requires higher order mean field methods. Our results illustrate finite- and infinite-body collective effects in symmetric and
symmetry-lacking systems.
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Physics Education · Cross-listed from cs.CL
Stan: An LLM-based thermodynamics course assistant
Eric M. Furst and Vasudevan Venkateshwaran
Discussions of AI in education focus predominantly on student-facing tools – chatbots, tutors, and problem generators – while the potential for the same infrastructure to support instructors remains largely unexplored. We describe Stan, a suite of tools for an undergraduate chemical engineering thermodynamics course built on a data pipeline that we develop and deploy in dual roles: serving students and supporting instructors from a shared foundation of lecture transcripts and a structured textbook index. On the student side, a
retrieval-augmented generation (RAG) pipeline answers natural-
language queries by extracting technical terms, matching them against the textbook index, and synthesizing grounded responses with specific chapter and page references. On the instructor side, the same transcript corpus is processed through structured analysis pipelines that produce per-lecture summaries, identify student questions and moments of confusion, and catalog the anecdotes and analogies used to motivate difficult material – providing a searchable, semester-scale record of teaching that supports course reflection, reminders, and improvement. All components, including
speech-to-text transcription, structured content extraction, and interactive query answering, run entirely on locally controlled hardware using open-weight models (Whisper large-v3, Llama~3.1 8B) with no dependence on cloud APIs, ensuring predictable costs, full data
privacy, and reproducibility independent of third-party services. We describe the design, implementation, and practical failure modes encountered when deploying 7–8 billion parameter models for structured extraction over long lecture transcripts, including context truncation, bimodal output distributions, and schema drift, along with the mitigations that resolved them.
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Optics
Hybrid Longitudinal-Transverse Propagating Electric Fields in Photonic Crystal Waveguides
Yanrong Zhang, Hooman Barati Sedeh, Christopher S. Whittington et al. (+3 more)
In a uniform, source-free, and unbounded medium, Maxwell's equations require electromagnetic waves to be purely transverse. However, when a beam of light is tightly focused or strongly confined, a longitudinal field component can emerge. Strong longitudinal fields enable many novel phenomena and applications, including single molecule detection, near-field imaging, and high-resolution photolithography. Although the behavior of the longitudinal electric (LE) field component of the electromagnetic field in ordinary waveguides is well established, judicious nanostructuring offers unprecedented control over its strength as well as spatial and spectral distribution. Here, we demonstrate a full-vectorial theory and experimental results showing that for specially designed waveguides, such as one-dimensional antislot photonic
crystal (PhC) waveguides, the LE field can hybridize with the transverse electric (TE) field in the waveguide and can be subsequently decomposed into independent polarizations through far field imaging. When the in-plane mirror
symmetry of a PhC unit
cell is broken, coupling between LE and TE modes produces two hybrid LE-TE modes and opens a new photonic bandgap. The LE-TE composition of the hybrid modes and the width of the resulting bandgap can be tuned by changing the rotation angle of the antislot within the unit
cell. We show that a 45-degree antislot orientation with respect to the propagation direction yields hybrid modes with the largest LE field contribution and the widest geometry-induced bandgap. Such engineered PhC waveguides enable new on-chip photonic functionalities, including in-plane angle-invariant dipole coupling in
quantum systems, higher-order polarization-division multiplexing, and enhanced control of light flow.
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All authors Yanrong Zhang, Hooman Barati Sedeh, Christopher S. Whittington, Natalia M. Litchinitser, Shuren Hu, Sharon M. Weiss
Applied Physics · Cross-listed from cond-mat.soft
Md Sakhawat Hossain Himel, James T. Gleeson, Robert J. Twieg et al. (+2 more)
Chiral nematic
liquid crystals are one-dimensional photonic band-gap materials whose reflection wavelength can be well tuned by temperature, but only limited and irreversible tuning can be achieved by electric fields. In contrast, oblique heliconical
chiral nematic materials blueshift with <1kV/mm fields applied along the helix axis, whereas
chiral ferroelectric nematic
liquid crystals can be redshifted by <0.1kV/mm fields applied perpendicular to the helix axis. Here we demonstrate that in ferroelectric nematic
liquid crystals, the reflection color can be reversibly tuned also by electric fields applied along the helix axis. In sandwich
cells assembled with bare conducting indium tin
oxide (ITO) substrates, the reflectivity peak wavelength increases by up to 200 nm under fields up to 0.4 kV/mm. When the ITO substrates are treated with an electrically insulating
polymer layer, the reflectivity shift is suppressed. We propose a theoretical model assuming helical deformation of the helix axis under electric field. This model accounts for all observations and also yields an estimate of the splay elastic constant which is challenging to determine by other methods. Our findings expand understanding of ferroelectric nematic
liquid crystals and suggest potential applications in both tunable reflectors and energy-efficient smart windows.
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All authors Md Sakhawat Hossain Himel, James T. Gleeson, Robert J. Twieg, Samuel Sprunt, Antal Jakli
Physics Education
Chatbot Conversations in Physics Education: Using Artificial Intelligence to Analyze Student Reasoning through Computational Grounded Theory
Atharva Dange and Ramon E. Lopez
This study applies Computational Grounded Theory (CGT) to analyze student misconceptions using interaction data from an AI-powered chatbot deployed in a university-level Modern Physics course. The chatbot - the UTA Study Buddy Bot - engaged students in peer-like problem-solving conversations throughout the semester, generating a rich
dataset of over 10 million
tokens. To explore patterns in student
reasoning and identify recurring conceptual difficulties, we implemented a CGT pipeline that combined natural
language processing, unsupervised clustering of sentence-level vector
embeddings, human interpretation of emergent themes, and supervised learning to evaluate the generalizability of identified categories. Preliminary results revealed persistent misconceptions in areas such as relativistic momentum and
quantum energy levels, along with distinctive trends in how students phrased their questions and expressed uncertainty. These findings underscore the potential of CGT as a scalable, theory-aligned approach for extracting insights from chatbot dialogues and guiding the development of more adaptive, AI-driven educational tools in physics instruction.
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Plasma Physics · Cross-listed from cs.LG
PDE foundation model-accelerated inverse estimation of system parameters in inertial confinement fusion
Mahindra Rautela, Alexander Scheinker, Bradley Love et al. (+4 more)
PDE foundation models are typically pretrained on large, diverse corpora of PDE
datasets and can be adapted to new settings with limited task-specific data. However, most downstream evaluations focus on forward problems, such as autoregressive rollout prediction. In this work, we study an inverse problem in inertial confinement fusion (ICF): estimating system parameters (inputs) from multi-modal, snapshot-style observations (outputs). Using the open JAG
benchmark, which provides hyperspectral X-ray images and scalar observables per simulation, we finetune the PDE foundation model and train a lightweight task-specific head to jointly reconstruct hyperspectral images and regress system parameters. The fine-tuned model achieves accurate hyperspectral reconstruction (test MSE 1.2e-3) and strong parameter-estimation performance (up to R^2=0.995). Data-scaling experiments (5%-100% of the training set) show consistent improvements in both reconstruction and regression losses as the amount of training data increases, with the largest marginal gains in the low-data regime. Finally, finetuning from pretrained MORPH weights outperforms training the same architecture from scratch, demonstrating that foundation-model initialization improves sample efficiency for data-limited inverse problems in ICF.
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All authors Mahindra Rautela, Alexander Scheinker, Bradley Love, Diane Oyen, Nathan DeBardeleben, Earl Lawrence, Ayan Biswas
Optics · Cross-listed from cond-mat.str-el
Thermodynamics of the ultrafast phase transition of vanadium dioxide
Shreya Bagchi, Ernest Pastor, José Santiso et al. (+2 more)
Ultrafast photoexcitation is an emerging route to selective control of phase transitions. However, it is difficult to determine which modes govern the transformation and how effectively they are targeted by photoexcitation. This is exemplified in vanadium dioxide, which transitions from a monoclinic
insulator to a rutile metal upon heating or photoexcitation. There is a long-standing debate about whether this transition is electronically or structurally driven and whether the structural component is coherent, driven by a single structural mode or thermal in nature. In this work, we develop a simple thermodynamic framework based on temperature-dependent ultrafast pump-probe measurements and contrast it to microscopic-detail-free modelling to identify the driving mechanism of the transition, revealing that population of the full thermal
phonon spectrum, especially high-frequency oxygen modes, is necessary to stabilize the metallic phase. Our approach can straightforwardly be applied to determine the nature of other photoinduced phase transitions without the need for complex multi-messenger experiments and can guide new control strategies, even for incoherent transitions.
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All authors Shreya Bagchi, Ernest Pastor, José Santiso, Allan S. Johnson, Simon E. Wall
Atomic Physics
Fundamental linewidth limit of electromagnetically induced transparency in a thermal Rydberg ladder
Noah Schlossberger, Nikunjkumar Prajapati, Alexandra B. Artusio-Glimpse et al. (+2 more)
Spectroscopy of Rydberg states has become a popular platform for
quantum sensing, with the most common readout scheme being two-
photon electromagnetically induced transparency (EIT) using counter-propagating
laser beams. In this scheme, the energy resolution of the Rydberg state is set by the spectral linewidth of the EIT feature. While selection criteria for the two-
photon resonance can narrow the linewidth to the order of the Rydberg state decay rate for a single atom, the Doppler shift from thermal velocity of the atoms broadens the ensemble linewidth to the order of the decay rate of the intermediate state. Here, we derive an analytic expression for the Doppler residual lineshape in the low-power limit and corroborate the results with experiment. For Rb, we find the full-width at half-maximum linewidth limit to be 1.84 MHz when scanning the coupling
laser and measure an experimental linewidth of 2.04 MHz. These linewidths are around a factor of two narrower than previous theoretical estimates as well as previously reported measured linewidths. With this, we demonstrate the most precise two-
photon energy resolution of a Rydberg state in thermal vapor to date. We then map out broadening mechanisms near this limit.
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All authors Noah Schlossberger, Nikunjkumar Prajapati, Alexandra B. Artusio-Glimpse, Samuel Berweger, Christopher L. Holloway
Atomic Physics · Cross-listed from quant-ph
Photon statistics in chiral waveguide QED: I Mean field and perturbative expansions
M. Eltohfa and F. Robicheaux
Waveguide
Quantum Electrodynamics (WQED) offers a suitable stage for controlling the interaction of light with atoms, allowing for collective phenomena such as super- and subradiance. In a
chiral waveguide setup, the
quantum state evolves through all the
Hilbert space, rendering an exact theoretical treatment exponentially hard and unobtained to date for more than $\sim 20$ atoms. In this work, we use a computationally efficient higher order mean-field approximation to model the radiation dynamics in a chirally coupled array of atoms, showing good agreement with recent experimental results. Further, based on a perturbative approximation of the full dynamics, we develop an analytical solution that captures
photon statistics for a moderate atom number, $N$, and a homogeneous atom-waveguide coupling, $\beta$. Finally, we show that capturing the onset of second-order coherence from a fully inverted state requires a fourth-order mean-field approximation, as lower-order treatments fail to account for the necessary four-body correlations. These results illustrate the complex behavior of a
symmetry-lacking system, and the methods discussed here provide systematic analytical solutions to which semi-classical methods such as the cumulant expansion or the truncated Wigner approximation can be benchmarked.
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Optics · Cross-listed from quant-ph
High Purity OAM Entangled Photons from SPDC with Reduced Spatial Spectral Correlations
F. Crislane V. de Brito, Sylwia Kolenderska and Piotr Kolenderski
Entanglement generated by Spontaneous Parametric Down Conversion (SPDC) involves multiple, often mutually correlated degrees of freedom. These degrees of freedom are often treated independently, overlooking the intrinsic correlation between them. We focus on the spatial spectral correlations that, if left uncontrolled, introduce distinguishability and reduce coherence, undermining applications such as high-dimensional OAM encoding. We analyze the spatio spectral structure of the biphoton and identify source configurations enabling a strong reduction of such correlations. We then quantify how spatial spectral coupling degrades OAM spatial purity, mapping high-purity regions as functions of OAM order,
crystal length, and pump/collection waists. The resulting design parameters enable engineering bright, high purity OAM entangled sources, reducing the need for loss-introducing filtering and therefore supporting scalable high-dimensional photonic
quantum technologies.
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Classical Physics · Cross-listed from gr-qc
Aspects of Relativity in Flat Spacetime
C. J. Papachristou
A monograph on the mathematical aspects of Special Relativity, focusing on the Lorentz group and the properties of relativistic transformations in mechanics and electrodynamics. Manuscript of published book, with added appendices.
Chemical Physics
How to improve the accuracy of semiclassical and quasiclassical dynamics with and without generalized quantum master equations
Matthew R. Laskowski, Srijan Bhattacharyya and Andrés Montoya-Castillo
Semi- and quasi-classical (SC) theories can handle arbitrary interatomic interactions and are thus well-suited to predict
quantum dynamics in condensed phases that encode energy and charge transport, spectroscopic responses, and chemical reactivity. However, SC theories can be computationally expensive and inaccurate. When combined with generalized
quantum master equations (GQMEs), the resulting SC-GQMEs have been observed to enhance the efficiency and accuracy of SC dynamics. Yet, while the mechanism responsible for improved efficiency is clear, the underlying improved accuracy remains elusive. What is worse, SC-GQMEs can yield unphysical dynamics in challenging parameter regimes – a shortcoming that might be avoided if the mechanism of accuracy improvement were understood. Here, we uncover this mechanism. We leverage short-time analyses to prove that exact, "left-handed" time-derivatives delay the onset of SC inaccuracy, and show that their numerical integration yields dynamics with improved accuracy, even without the GQME. We find, however, that these derivatives are a double-edged sword: while offering greater short-time accuracy, they become unphysical in challenging parameter regimes. Because short-lived
memory kernels can leverage short-time accuracy while circumventing long-time instability, we develop a protocol to unambiguously determine the
memory kernel cutoff, even in challenging regimes where previous treatments had failed. Our insights into accuracy improvement and kernel cutoff protocol can be expected to apply to complex systems that go beyond simple models.
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Computational Physics · Cross-listed from astro-ph.EP
A Comparative Study of the Streaming Instability: Unstratified Models with Marginally Coupled Grains
Stanley A. Baronett, Wladimir Lyra, Hossam Aly et al. (+19 more)
The streaming instability is a leading mechanism for concentrating solids and initiating planetesimal formation in protoplanetary disks. Although numerous studies have explored its linear growth, nonlinear
evolution, and implications for
planet formation, the diversity of numerical methods and
dust treatments used across the literature has made it difficult to assess which features of the instability are physically robust and which arise from code-dependent choices. We present the first systematic comparison of seven hydrodynamic codes–spanning finite-volume and finite-difference schemes and modeling
dust either as Lagrangian particles or as a pressureless fluid–applied to the unstratified streaming instability with a dimensionless stopping time of unity. All codes reproduce the characteristic sequence of exponential growth, filament formation, and turbulent saturation, demonstrating broad agreement in the qualitative behavior of the instability. Quantitatively, however, the
dust model remains the dominant source of variation at moderate resolution: particle-based simulations reach higher peak densities and exhibit broader high-density tails than fluid-based models at $512^2$ resolution, although increasing the number of particles brings their initial maximum density
evolution into close agreement with that of
dust-fluid models. At $1024^2$, these differences diminish substantially, indicating better agreement of the saturated-state statistics across
dust treatments. In terms of computational performance, most particle implementations suffer from imbalanced parallelized loads, while execution on a GPU is at least two to three times more energy efficient and scales better at higher resolutions than on CPUs. Given the intrinsic stochasticity of this nonlinear system, only statistical diagnostics remain meaningful across codes.
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All authors Stanley A. Baronett, Wladimir Lyra, Hossam Aly, Olivia Brouillette, Daniel Carrera, Victoria I. De Cun, Linn E. J. Eriksson, Mario Flock, Pinghui Huang, Leonardo Krapp, Geoffroy Lesur, Rixin Li, Shengtai Li, Jeonghoon Lim, Sijme-Jan Paardekooper, David G. Rea, Debanjan Sengupta, Jacob B. Simon, Prakruti Sudarshan, Orkan M. Umurhan, Chao-Chin Yang, Andrew N. Youdin
Chemical Physics
Projected Hessian Learning: Fast Curvature Supervision for Accurate Machine-Learning Interatomic Potentials
Austin Rodriguez, Justin S. Smith, Sakib Matin et al. (+3 more)
The Hessian
matrix (second derivatives) encodes far richer local
curvature of the potential energy surface than energies and forces alone. However, training machine-learning interatomic potentials (MLIPs) with full Hessians is often impractical because explicitly forming and storing Hessian
matrices scales quadratically in cost and
memory. We introduce Projected Hessian Learning (PHL), a scalable second-order training framework that injects
curvature information using only Hessian-vector products (HVPs). Rather than constructing the Hessian, PHL projects
curvature along
stochastic probe directions and uses an unbiased
stochastic trace-based loss with favorable system-size scaling, enabling
curvature-informed training without quadratic
memory growth. We
benchmark PHL on a chemically diverse
dataset of reactants, products, transition states, intrinsic reaction coordinates, and normal-mode sampled geometries computed at omegaB97XD/6-31G(d). We compare energy-force training (E-F), two HVP-based schemes (E-F-HVP with one-hot or randomized probes), and full energy-force-Hessian training (E-F-H). With randomized probes per minibatch, both HVP schemes match full-Hessian training in energy, force, and Hessian accuracy while delivering >24x epoch speedups for the small molecular systems studied. In a fixed-probe regime with one HVP per molecule, randomized projections consistently outperform one-column probing, especially for far-from-
equilibrium geometries. Overall, PHL replaces explicit Hessian supervision with force-complexity
curvature training, retaining most second-order accuracy gains while scaling to larger, more complex molecular systems.
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All authors Austin Rodriguez, Justin S. Smith, Sakib Matin, Nicholas Lubbers, Kipton Barros, Jose L. Mendoza-Cortes
Applied Physics · Cross-listed from quant-ph
Fundamental Limits on Polarization Entanglement Distribution in Optical Fiber
Stefano Pirandola
Characterizing the ultimate rates of
entanglement distribution is essential for both foundational research and the practical deployment of
quantum technologies. To investigate these limits, we introduce an erasure-Pauli channel model describing the distribution of polarization
entanglement in optical fiber. For this channel, we derive bounds on the rates of
entanglement distribution and related
quantum resources under optimal local operations and two-way classical communication (two-way assisted capacities). This framework allows us to determine the optimal repeaterless performance achievable over realistic optical fibers affected by polarization mode dispersion, thereby providing a rigorous
benchmark for long-distance polarization-based
quantum communication. Finally, we show that both our model and capacity bounds remain robust under the inclusion of detector dark counts.
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Optics
Realizing anomalous Floquet non-Abelian band topology in photonic scattering networks
Yuze Hu, Mingyu Tong, Tian Jiang et al. (+10 more)
The concept of multi-gap
topology has recently been shown to give rise to uncharted phases beyond conventional single-gap classifications. These phases relate to band nodes with non-Abelian quaternion charges and momentum-space braiding processes characterized by new invariants such as paradigmatic Euler class, phenomena that intrinsically require at least two spatial dimensions. Extending such phases into the non-
equilibrium regime is predicted to unlock even richer multi-gap
topologies beyond static settings, yet their experimental realization has remained elusive due to the stringent requirements on dimensionality,
symmetry, and dynamical control. Here, we theoretically demonstrate and, for the first time, experimentally realize two-dimensional (2D) Floquet non-Abelian band
topology in photonic scattering networks. Within this platform, we uncover a sequence of topological phenomena unique to 2D multi-gap systems far from
equilibrium, including anomalous multi-gap phases interconnected by band nodes, Floquet Euler transfer, gapped phases with anomalous Dirac string configurations, and Floquet-induced non-Abelian braiding of band nodes. In addition, we observe Floquet-periodic anomalous edge states across multiple gaps, providing experimental signatures of these sought-after 2D multi-gap Floquet topological phases. Our results establish photonic scattering networks as a practical and versatile route to non-Abelian Floquet systems, opening avenues for dynamical topological physics with braiding capability and robust photonic functionalities.
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All authors Yuze Hu, Mingyu Tong, Tian Jiang, Shuxing Yang, Ning Han, Fujia Chen, Li Zhang, Rui Zhao, Qiaolu Chen, Hongsheng Chen, F. Nur Ünal, Robert-Jan Slager, Yihao Yang
Chemical Physics · Cross-listed from cond-mat.mes-hall
Coherent Biexciton Transport in the Presence of Exciton-Exciton Annihilation in Molecular Aggregates
Rajesh Dutta and Chern Chuang
We present a theoretical framework for biexciton dynamics in molecular aggregates that explicitly treats populations and coherences across excitation
manifolds within a reduced density-
matrix formalism. By extending kinetic descriptions beyond the weak-coupling limit, the approach captures the influence of
exciton delocalization and
exciton-
exciton annihilation while remaining computationally tractable within a Markovian description of environmental relaxation. Using this framework, we investigate how the spatial profile and momentum composition of the initial biexciton state govern fluorescence decay and transport. Incoherent initial conditions lead to strongly non-exponential relaxation and time-dependent
diffusion driven by nonlinear population kinetics. In contrast, coherently prepared biexciton states exhibit pronounced early-time coherent transport, whose character depends sensitively on whether the initial state is prepared as a standing-wave or traveling-wave superposition of single-
exciton modes. Despite nearly identical emission dynamics for J and H aggregate, biexciton transport properties differ markedly due to band structure-dependent interference effect. Our results demonstrate that biexciton dynamics remains strongly influenced by initial-state coherence and momentum composition. Besides initial-state preparation, the coherent-to-incoherent crossover and the diffusive spreading of the
exciton density are sensitive to internal conversion processes such as
exciton fusion and the decay to the first excited state. The present work establishes initial-state preparation as a key control parameter for many-
exciton transport in excitonic systems and provides a general framework for interpreting nonlinear optical experiments beyond population-based descriptions.
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Optics
Simulation of Hopfield-like Hamiltonians using time-multiplexed photonic networks
Théophile Seck, Hugo Lumia, Edwin Ng et al. (+1 more)
We propose a time-multiplexed photonic network architecture based on coupled ring resonators, capable of accurately emulating specific
Hamiltonian dynamics. We show that, in the Suzuki-Trotter limit, the resulting stroboscopic
evolution reproduces the characteristic dynamics of the bosonized Hopfield model. Furthermore, by incorporating a nonlinear element within the main resonator loop, we outline a scalable route toward optical simulation of both mean-field and
quantum nonlinear dynamics associated with the Tavis-Cummings model. Our results establish time-multiplexed resonator networks as a versatile photonic framework for simulating interacting light-matter
Hamiltonians and collective many-body phenomena.
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All authors Théophile Seck, Hugo Lumia, Edwin Ng, Thibault Chervy
Instrumentation and Detectors
Commissioning and Full Realization of the PLASEN System at BRIF
W. C. Mei, H. R. Hu, Y. F. Guo et al. (+37 more)
A PLASEN (Precision
LAser Spectroscopy for Exotic
Nuclei) system, consisting of a compact
radio-frequency quadrupole cooler-buncher (RFQ-cb) and a collinear resonance ionization spectroscopy setup, has now been fully commissioned with radioactive ion beams at the Beijing Radioactive Ion-beam Facility (BRIF). Using both stable and radioactive Rb ion beams from BRIF, we demonstrated that the large beam energy spread observed at BRIF has been successfully handled by employing the RFQ-cb, enabling the delivery of high-quality bunched radioactive ion beams for collinear resonance ionization spectroscopy experiments. Under these conditions, we performed
laser spectroscopy of exotic
nuclei, achieving high resolution (about 100 MHz spectral linewidth) and high sensitivity (up to 1:200 efficiency). This fully operational PLASEN system will serve as a state-of-the-art experimental platform at BRIF for research in multiple fields such as
nuclear, atomic and molecular physics.
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All authors W. C. Mei, H. R. Hu, Y. F. Guo, Z. Yan, X. F. Yang, S. J. Chen, D. Y. Chen, Y. P. Lin, Y. S. Liu, C. Zhang, Y. P. Jing, T. X. Gao, X. Shen, Y. Y. Jia, Y. T. Lin, H. X. Zhang, S. W. Bai, B. Tang, X. Ma, G. F. Song, S. Ye, M. Y. Lu, J. Y. Dong, B. K. Dong, J. H. Lv, S. Y. Dong, F. C. Liu, Z. Hu, X. Liu, S. T. Zhu, Y. L. Yi, C. Y. He, A. Takamine, B. Q. Cui, J. Yang, Z. Y. Liu, J. Su, H. N. Liu, Y. L. Ye, B. Guo
Instrumentation and Detectors
Experiments towards a neutron target for measurements in inverse kinematics
S.F. Dellmann, C.M. Harrington, O.R. Cantrell et al. (+28 more)
Neutron-induced reactions play an important role in fundamental
nuclear physics,
nuclear astrophysics, and applications. In the case of reactions on rare isotopes, there are limited options for direct experimental measurements. The
Neutron Target Demonstrator project at Los Alamos National Laboratory seeks to test the feasibility of moderating spallation
neutrons within a 1~m$^3$ graphite cube to create a standing
neutron target for
neutron-induced reaction measurements in inverse kinematics. This paper presents the results of experimental
neutron flux distribution tests using
neutron sources (ranging from 1~keV to 50~MeV) created by accelerators at the University of Notre Dame and Texas A&M University. Measurements were made with both the full graphite cube as well as a ”half cube” setup in which half of the graphite cube was removed. The measured distributions agree with simulated distributions in the case of the full cube moderator, although there remain discrepancies in certain cases for the half cube moderator. The results shown here will provide useful information for an upcoming experimental campaign to test the
neutron target proof-of-principle.
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All authors S.F. Dellmann, C.M. Harrington, O.R. Cantrell, A.L. Cooper, A. Couture, D.V. Gorelov, I. Knapová, S.M. Mosby, R. Reifarth, A. Alvarez, A. Aprahamian, J. Butz, I.J. Bos, M.T. Febbraro, T. Hankins, B.M. Harvey, T. Heftrich, M. Le, J.J. Manfredi, A.B. McIntosh, K.V. Manukyan, M. Matney, S. Regener, D. Robertson, A. Simon, D. Sokolovic, E. Stech, G. Tabacaru, W. Tan, M. Wiescher, S. Yennello
Instrumentation and Detectors · Cross-listed from nucl-ex
The MexNICA Collaboration in the MPD-NICA Experiment at JINR: Experimental and Theoretical Achievements
Alfredo Raya, Mauricio Alvarado, Juan Anzúrez et al. (+21 more)
The MexNICA Collaboration coordinates the activities of Mexican scientists, engineers, postdoctoral fellows and students in the Multi-Purpose Detector experiment at the Nuclotron-based Ion
Collider fAcility of the Joint Institute for
Nuclear Research in Dubna, Russia. Established in 2016, the collaboration brings together five Mexican institutions whose contributions span detector development as well phenomenological and theoretical studies, including modeling by means of Monte Carlo simulations. This work summarizes the main achievements of MexNICA, consisting of the development of the miniBeBe trigger detector as well of results of phenomenological investigations of the
baryon-rich region in the QCD phase diagram accessible at NICA energies, and theoretical advances based on
lattice QCD and effective models.
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All authors Alfredo Raya, Mauricio Alvarado, Juan Anzúrez, Alejandro Ayala, Wolfgang Bietenholz, Salomón Borjas García, Eleazar Cuautle, Pedro E. García González, Irving Iván Gaspar Gregorio, Isabel Domínguez, Luis Alberto Hernández, Maribel Herrera, Israel Luna, Pablo Martínez-Torres, Emanuel Nolasco Gómez, Miguel Enrique Patiño, Manuel Elías Pech Dzul, Juan Carlos Ramírez Márquez, Mauricio Reyes Gutiérrez, Ulises Sáenz-Trujillo, Roberto Tapia Sánchez, María Elena Tejeda-Yeomans, Galileo Tinoco-Santillán, Carlos Rafael Vázquez Villamar
Atmospheric and Oceanic Physics · Cross-listed from cs.LG
Accurate and Efficient Hybrid-Ensemble Atmospheric Data Assimilation in Latent Space with Uncertainty Quantification
Hang Fan, Juan Nathaniel, Yi Xiao et al. (+5 more)
Data assimilation (DA) combines model forecasts and observations to estimate the optimal state of the atmosphere with its uncertainty, providing initial conditions for weather prediction and reanalyses for
climate research. Yet, existing traditional and machine-learning DA methods struggle to achieve accuracy, efficiency and uncertainty quantification simultaneously. Here, we propose HLOBA (Hybrid-Ensemble Latent Observation-Background Assimilation), a three-dimensional hybrid-ensemble DA method that operates in an atmospheric latent space learned via an autoencoder (AE). HLOBA maps both model forecasts and observations into a shared latent space via the AE encoder and an end-to-end Observation-to-Latent-space mapping network (O2Lnet), respectively, and fuses them through a
Bayesian update with weights inferred from time-lagged ensemble forecasts. Both idealized and real-observation experiments demonstrate that HLOBA matches dynamically constrained four-dimensional DA methods in both analysis and forecast skill, while achieving end-to-end inference-level efficiency and theoretical flexibility applies to any
forecasting model. Moreover, by exploiting the error decorrelation property of latent variables, HLOBA enables element-wise uncertainty estimates for its latent analysis and propagates them to model space via the decoder. Idealized experiments show that this uncertainty highlights large-error regions and captures their seasonal variability.
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All authors Hang Fan, Juan Nathaniel, Yi Xiao, Ce Bian, Fenghua Ling, Ben Fei, Lei Bai, Pierre Gentine
Optics
Hyperuniform Disorder in Photonic Crystal Slabs with Intrinsic non-Hermiticity
Zeyu Zhang, Koorosh Sadri, Brian Gould et al. (+1 more)
Hyperuniform disorder is a type of correlated disorder characterized by vanishing spectral density at small wavevectors, making the configuration effectively homogeneous on long length scales. In photonics, hyperuniform disorder is promising for generating isotropic photonic pseudogaps and engineering photonic
crystal waveguides. However, these studies are largely restricted to idealized lossless settings, although all photonic systems necessarily have loss. In this work, light propagation in photonic
crystal slabs with imposed hyperuniform disorder is investigated theoretically and numerically. The system is intrinsically non-Hermitian due to radiative loss, with non-Hermiticity appearing as a complex effective mass of a quadratic photonic band. A theoretical framework for disorder scattering is analytically derived in Hermitian and non-Hermitian quadratic bands with real and complex effective mass, respectively. In contrast to the power law behavior $|\mathbf{k}|^\alpha$ observed in the Hermitian case (where $\alpha$ is the hyperuniformity exponent), the scattering loss in the non-Hermitian band is given by $C_0+C_{\beta_2}\cdot|\mathbf{k}|^{\beta_2}$, where $C_0$ is a finite constant and the exponent $\beta_2\leq 2$. Our theoretical predictions are verified with tight-binding and Finite-Difference Time-Domain simulations with realistic photonic
crystal parameters, based on recent experiments.
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All authors Zeyu Zhang, Koorosh Sadri, Brian Gould, Mikael Rechtsman
Fluid Dynamics · Cross-listed from cond-mat.soft
Dynamic properties in a collisional model for confined granular fluids. A review
Ricardo Brito, Rodrigo Soto and Vicente Garzó
Granular systems confined in a shallow box and driven by vertical vibration provide a simple geometry to study fluidized granular media. Grains gain kinetic energy vertically through collisions with the walls and redistribute it horizontally via interparticle collisions. The $\Delta$-model has been proposed as a simplified description of this setup. In this model, a fixed velocity increment $\Delta$ is added to the normal component of the relative velocity at collisions, effectively integrating out the vertical motion while preserving collisional energy injection. This compensates for inelastic losses and yields stable homogeneous steady states amenable to kinetic theory. An Enskog kinetic equation is formulated and analyzed to obtain the stationary temperature and equation of state. The Chapman–Enskog method is then applied to derive the Navier–Stokes transport coefficients and study inhomogeneous states. The theory is extended to granular mixtures with different masses, sizes, restitution coefficients, or $\Delta$ values, leading to nonequipartition of energy even in homogeneous states. The resulting hydrodynamic equations, with transport coefficients obtained in the low-density regime, show unconditional stability of the homogeneous state and violation of Onsager reciprocity. Theoretical predictions agree well with molecular dynamics and direct simulation Monte Carlo results.
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Fluid Dynamics
Volumetric effects in viscous flows in circular and annular tubes with wavy walls
Yisen Guo and John H. Thomas
We point out that, in the usual way of specifying a sinusoidal waviness of the wall of a tube of circular cross section, in which the mean radius is kept constant, the interior volume of the tube increases with increasing wave amplitude. We compare this case with the case where the interior volume is kept constant by reducing the mean radius as the wave amplitude increases. We present and compare numerical results of these two cases for steady, pressure driven, laminar viscous flow in a tube with a stationary wavy wall, for both circular and annular tubes. The volume flow rate and the hydraulic resistance can differ in the two cases by as much as 10% for wave amplitudes as small as 20% of the mean radius and as much as 50% for larger wave amplitudes. For a circular tube, we derive a scaling law that relates the two cases based on dimensional analysis, allowing the behavior in the constant-volume case to be determined from that in the constant-mean-radius case. Additionally, we consider peristaltic pumping due to a moving sinusoidal wall wave and show that the volume-change effect is significant even at small wave amplitudes, and that the volume flow rates in the two cases can differ significantly, by as much as 50% as the wave amplitude approaches its maximum value.
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Instrumentation and Detectors · Cross-listed from cond-mat.mes-hall
Sub-wavelength mid-infrared imaging of locally driven photocurrents using diamond campanile probes
Rajasekhar Medapalli, Nathan D. Cottam, Khushboo Agarwal et al. (+12 more)
Precise and high efficiency concentration of mid-infrared (mid-IR) light into sub wavelength volumes is essential for probing low-energy excitations and achieving strong field enhancements, which can be hindered by absorption losses and coupling inefficiencies at long wavelengths. Here, we introduce an innovative diamond-based metal-
insulator-metal campanile probe that adiabatically compresses free-space mid infrared light (10 \mum) into \approx 1 \mum domains. Integrated into a scanning photovoltage microscope, the probe enables sub-wavelength mapping of locally driven photocurrents in
graphene, resolving polarization dependent and contact-sensitive responses at energies down to \approx 0.1 eV. Experiments reveal a photocurrent signal density enhancement of 10^3 and coupling efficiencies approaching 80%, in agreement with numerical simulations. Operation of the probe with
quantum cascade and free electron
lasers demonstrates a robust, spectrally tunable platform for high-resolution exploration of low-energy carrier dynamics in atomically thin materials, opening opportunities for mid-IR optoelectronics and
quantum photonics.
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All authors Rajasekhar Medapalli, Nathan D. Cottam, Khushboo Agarwal, Benjamin T. Dewes, Nils Dessmann, Sergio Gonzalez-Munoz, Wenjing Yan, Vaidotas Mišeikis, Sergey Kafanov, Rostislav V. Mikhaylovskiy, Samuel P. Jarvis, Camilla Coletti, Britta Redlich, Amalia Patanè, Oleg V. Kolosov
Fluid Dynamics
Grid-agnostic volume of fluid approach with interface sharpening and surface tension for compressible multiphase flows
J. Marziale, J. Sun, D. Salac et al. (+1 more)
The interfacial
diffusion associated with finite volume method (FVM) discretizations of multiphase flows creates the need for an interface sharpening mechanism. Such solutions for structured quadrilateral grids are well documented, but various engineering applications require mesh designs specific to the irregular geometry of the physical system it is modeling. Therefore this study casts interface sharpening as an ant-idiffusive volumetric body force whose calculation procedure is generalizable to an arbitrarily constructed grid. The force magnitude is derived at
cell centers as a function of the local compressible flow characteristics and the geometry of the
cell neighborhood. The flow model uses an AUSM+up based method for flux evaluation and imposes a stiffened equation of state onto each of the fluids in order to close the linear system and extract auxiliary variables. Validation tests show good agreement with the Young-Laplace condition whereby the interface converges to the analytical solution corresponding to a balance between a pressure jump and interfacial forces. Further results show the recovery of a circle starting from a shape with highly variational
curvature through the combined effects of surface tension and interface sharpening. Lastly shear-driven droplet pinchoff results show good agreement with droplet shapes provided by the surrounding literature at various Weber-Ohnesorge number combinations.
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All authors J. Marziale, J. Sun, D. Salac, J. Chen
Geophysics · Cross-listed from astro-ph.IM
Atmospheric effects on cosmic-ray muon rate at high latitude (78.9{\deg}N)
M. Abbrescia, C. Avanzini, L. Baldini et al. (+71 more)
Since 2019, three scintillator detectors of the EEE collaboration have been continuously measuring
cosmic muon rates at 78.9{\deg}N at the Ny-Ålesund Research Station (Svalbard). The resulting six-year time series reveals a pronounced annual modulation, driven primarily by seasonal atmospheric variations. Utilizing routine radiosonde profiles collected above the same site, we applied several established techniques –along with a tailored analysis approach– to investigate the relationship between
muon rate and atmospheric temperature. The temperature-corrected
muon-rates are analysed using the Lomb-Scargle periodogram technique in order to investigate the presence of remaining periodic structures. Finally, the temperature corrections coefficients of our analysis are compared with measurements in other stations located at lower latitudes.
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All authors M. Abbrescia, C. Avanzini, L. Baldini, R. Baldini Ferroli, G. Batignani, M. Battaglieri, S. Boi, E. Bossini, F. Carnesecchi, D. Cavazza, C. Cicalò, L. Cifarelli, F. Coccetti, E. Coccia, A. Corvaglia, A. De Caro, D. De Gruttola, S. De Pasquale, L. Galante, M. Garbini, L.E. Ghezzer, I. Gnesi, F. Gramegna, E. Gramstad, S. Grazzi, E.S. Haland, D. Hatzifotiadou, P. La Rocca, R. Liotino, Z. Liu, A. Lupi, G. Mandaglio, A. Margotti, G. Maron, M. N. Mazziotta, M. Mazzola, A. Mulliri, R. Nania, F. Noferini, F. Nozzoli, F. Ould-Saada, F. Palmonari, M. Panareo, M. P. Panetta, R. Paoletti, C. Pellegrino, L. Perasso, O. Pinazza, C. Pinto, S. Pisano, K. Piscicchia, L. Quaglia, M. Rasà, F. Riggi, G. Righini, C. Ripoli, M. Rizzi, B. Sabiu, G. Sartorelli, E. Scapparone, M. Schioppa, G. Scioli, A. Scribano, M. Selvi, A. Shtimermann, M. Taiuti, G. Terreni, A. Trifirò, M. Trimarchi, C. Vistoli, L. Votano, M. C. S. Williams, A. Zichichi, R. Zuyeuski
Plasma Physics
The self-generation of core fields and electron scattering in flux ropes during magnetic reconnection
Hanqing Ma, J. F. Drake and M. Swisdak
Two-dimensional particle-in-
cell simulations with a realistic mass ratio reveal the generation mechanisms of the out-of-plane
magnetic field in
magnetic islands/flux ropes during
magnetic reconnection. In the absence of an initial guide field, reconnection produces a large electron temperature anisotropy (around 4.5) inside
magnetic islands that drives the Weibel instability. Strong out-of-plane
magnetic fields (Bz/B0 around 0.4, greatly exceeding the
Hall field) with a regular bipolar structure grow inside islands. A space-time analysis reveals a one-to-one correspondence between the temperature anisotropy and the development of the Weibel
magnetic field. The instability relaxes the anisotropy, but island merging leads to anisotropy reemergence and re-excitation. In the presence of a strong ambient guide field (Bg/B0 = 0.5), the electron
outflow from the X-point deflects along the separatrices and forms a circular current loop wrapping the flux ropes. This flux-rope separatrix current generates an out-ofplane
magnetic field that reinforces the ambient guide field, reaching Bz/B0 around 1.4. The current can, in some cases, drive the electron Kelvin-Helmholtz instability, which produces electron
vortices and strengthens the
magnetic field. Mergers significantly broaden the islands and further strengthen the field. These self-generated out-of-plane
magnetic fields scatter electrons and reduce their temperature anisotropy, which can potentially affect electron heating via
Fermi reflection. The simulation results are supported by spacecraft observations suggesting that ambient guide fields can be enhanced within flux ropes in Earth's magnetotail.
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