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Physics Physics

physics Watch Physics

Monday 27 October

Instrumentation and Detectors

Search for dark matter Particles via Invisible Decays in ${}^{46}$Sc Nuclear $\gamma$ Cascades with a CsI(Tl) Detector

Sharada Sahoo, Jing-han Chen, Mahdi Mirzakhani et al. (+3 more)

Dark matter remains one of the most compelling open problems in modern physics, motivating experimental searches for new light, weakly coupled particles beyond the Standard Model. Despite extensive efforts employing diverse detection strategies, large regions of parameter space remain unexplored. We report a high-statistics laboratory search for invisible decay modes in nuclear $\gamma$-ray cascades using approximately $100~\mathrm{kg}$ of CsI(Tl) scintillators operated at Texas A&M University. The experiment employs a high-activity ${}^{46}$Sc radioactive source and a “missing-$\gamma$” technique, in which the absence of a photon from a well-identified cascade serves as a signature of new physics. Unlike appearance-disappearance experiments, this approach requires only a single photon conversion into a dark-sector particle, enabling sensitivity to significantly weaker couplings. The setup provides simultaneous sensitivity to a broad class of light dark-sector candidates, including axions and axion-like particles, dark scalars, and dark photons in the $0.1 - 1 \text{ MeV}$ mass region. Through careful control of detector containment, energy resolution, and environmental backgrounds, we exclude certain regions on the previously explored parameter space. With foreseeable improvements in detector volume and systematic uncertainty control, this technique has the potential to probe currently unexplored parameter space for axion-like particles and light dark scalars.
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All authors Sharada Sahoo, Jing-han Chen, Mahdi Mirzakhani, Harikrishnan Ramani, Rupak Mahapatra, Surjeet Rajendran

Fluid Dynamics

Analysis of accuracy and efficiency of neural networks to simulate Navier-Stokes fluid flows with obstacles

Rui Hespanha, Elliot McGuire and João Hespanha

Conventional fluid simulations can be time consuming and energy intensive. We researched the viability of a neural network for simulating incompressible fluids in a randomized obstacle-heavy environment, as an alternative to the numerical simulation of the Navier-Stokes equation. We hypothesized that the neural network predictions would have a relatively low error for simulations over a small number of time steps, but errors would eventually accumulate to the point that the output would become very noisy. Over a rich set of obstacle configurations, we achieved a root mean square error of 0.32% on our training dataset and 0.36% on a testing dataset. These errors only grew to 1.45% and 2.34% at t = 10 and, 2.11% and 4.16% at timestep t = 20. We also found that our selected neural network was approximately 8,800 times faster at predicting the flow than a conventional simulation. Our findings indicate neural networks can be extremely useful at simulating fluids in obstacle-heavy environments. Useful applications include modeling forest fire smoke, pipe fluid flow, and underwater/flood currents.
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Instrumentation and Detectors · Cross-listed from nucl-ex

Neutron capture measurement of the 165Ho at the CSNS Backn facility in the resonance energy region

De-Xin Wang, Su-Ya-La-Tu Zhang, Wei Jiang et al. (+17 more)

The neutron capture yield of 165Ho have been measured at the Back-streaming White neutron beam line (Back-n) of the China Spallation Neutron Source (CSNS) using a 4{\pi} BaF2 Gamma Total Absorption Facility (GTAF). The resonance shapes in the 1eV to 1.0keV region were analyzed with the Bayesian R-matrix code SAMMY. For 18 s-wave resonances below 100eV, the resonance energy ER, neutron width {\Gamma}n, and radiative width {\Gamma}{\gamma} were extracted. The statistical analyses of the resonance parameters show that the nearest-neighbour level-spacing distribution follows a Wigner-Dyson form with mean spacing D0 = 4.53(3)eV,indicating chaotic compound-nucleus behaviour; Using the extracted parameters, the s-wave neutron strength function for 165Ho was derived to be 10-4S0 = 2.01(1), in excellent agreement with the values reported in both the Atlas of Neutron Resonances and ENDF/B-VIII.0 data.
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All authors De-Xin Wang, Su-Ya-La-Tu Zhang, Wei Jiang, Rui-Rui Fan, Qi-Wei Zhang, Jie Ren, Jin-Cheng Wang, Guang-Yuan Luan, Xiao-Guang Wu, Bao-Hua Sun, Zhen-Xiang Zhou, Hong-Yi Wu, Zhi-Yang He, Cong-Bo Li, Qi Sun, Xuan Pang, Mei-Rong Huang, Guo Li, Gerile Bao, Xi-Chao Ruan

Fluid Dynamics

A parametric study of the broadband shock-associated noise in supersonic jets via semi-empirical modeling

Binhong Li and Benshuai Lyu

A semi-empirical model is developed in this paper to predict the broadband shock-associated noise (BBSAN) generated by shock-instability interaction (SII) in imperfectly expanded supersonic jets. The model makes use of a semi-empirically modified Pack's model that accounts for the decay in both shock amplitude and shock spacing and a Gaussian wave-packet model for the instability waves. The near-field pressure perturbation due to the SII is treated as a boundary value for the Helmholtz equation, which is subsequently solved to predict the far-field acoustic spectra and directivity patterns. A comprehensive parametric study is conducted to reveal the effects of the key parameters on the acoustic spectral and directivity features. It is found that decreasing the instability-wave decay rate narrows the spectral bandwidth and the major lobes in directivity patterns, while variations in shock spacing shift the spectral peak frequency and the major radiation angle. Mechanisms of such changes are discussed based on the model. Further validation against multiple experimental datasets demonstrates that incorporating more realistic parameters in the model-particularly those accounting for the shock spacing and amplitude decays-considerably improves its prediction accuracy and physical consistency. The improved model successfully reproduces several key spectral features observed in experiments; these include, for example, the peak frequency and the tendency of bandwidth contradiction as the observer angle increases. Moreover, the predicted directivity patterns closely match the experiments outside the shallow-angle region dominated by jet mixing noise. In particular, it captures the major radiation lobes and their frequency-dependent amplitude and shape variations.
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Fluid Dynamics

Gauss Principle in Incompressible Flow: Unified Variational Perspective on Pressure and Projection

Karthik Duraisamy

Following recent work, this manuscript clarifies what the Gauss-Appell principle determines in incompressible, inviscid flow and how it connects to classical projection methods. At a fixed time, freezing the velocity and varying only the material acceleration leads to minimization of a quadratic subject to acceleration-level constraints. First-order conditions yield a Poisson-Neumann problem for a reaction pressure whose gradient removes the non-solenoidal and wall-normal content of the provisional residual, precisely the well-known Leray-Hodge projection. Thus, Gauss-Appell enforces the instantaneous kinematic constraints and recovers Euler at the instant. Once the impressed physics is specified, for instance via external body forces, the reaction pressure is uniquely determined (up to an additive constant) as the Lagrange multiplier enforcing incompressibility and wall impermeability; it does no work on divergence-free, wall-tangent motions. This is the well-established interpretation of pressure in incompressible flow. The direct, fixed-time application of this principle determines the reaction pressure for an already-specified velocity field and does not, by itself, select circulation or stagnation points, because these are properties of the velocity state, not the instantaneous acceleration correction. The formal decomposition of the pressure into impressed and reaction components admits representational freedom that does not imply physical non-uniqueness of the constraint force. Orthogonality conventions such as Dirichlet orthogonality can fix the representational freedom as an additional modeling choice. This variational viewpoint also yields a simple computational diagnostic: the minimized Appellian equals a L2 norm of the reaction-pressure gradient which vanishes for constraint-compatible updates and grows with the magnitude of divergence and wall-flux mismatch.
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Computational Physics

Fast integration method for averaging polydisperse bubble population dynamics

Spencer H. Bryngelson

Ensemble-averaged polydisperse bubbly flow models require statistical moments of the evolving bubble size distribution. Under step forcing, these moments reach statistical equilibrium in finite time. However, the transitional phase before equilibrium and cases with time-dependent forcing are required to predict flow in engineering applications. Computing these moments is expensive because the integrands are highly oscillatory, even when the bubble dynamics are linear. Ensemble-averaged models compute these moments at each grid point and time step, making cost reduction important for large-scale bubbly flow simulations. Traditional methods evaluate the integrals via traditional quadrature rules. This approach requires a large number of quadrature nodes in the equilibrium bubble size, each equipped with its own advection partial differential equation (PDE), resulting in significant computational expense. We formulate a Levin collocation method to reduce this cost. Given the differential equation associated with the integrand, or moment, the method approximates it by evaluating its derivative via polynomial collocation. The differential matrix and amplitude function are well-suited to numerical differentiation via collocation, and so the computation is comparatively cheap. For an example excited polydisperse bubble population, the first moment is computed with the presented method at $10^{-3}$ relative error with 100 times fewer quadrature nodes than the trapezoidal rule. The gap increases for smaller target relative errors: the Levin method requires $10^4$ times fewer points for a relative error of $10^{-8}$. The formulated method maintains constant cost as the integrands become more oscillatory with time, making it particularly attractive for long-time simulations.
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Chemical Physics

QC Lab: A Python Package for Quantum-Classical Dynamics

Alex Krotz, Ethan Byrd, Ken Miyazaki et al. (+1 more)

QC Lab is an open-source Python package for QC dynamics simulations aimed to promote the development of QC algorithms, and their application to a wide variety of relevant model problems. It follows a modular design that facilitates cross-compatibility between algorithms and models. By decomposing algorithms and models into a series of tasks and ingredients that can be substituted and reused, it minimizes development efforts and code redundancy. In this Paper, we introduce the first stable release of QC Lab, and describe its design philosophy.
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All authors Alex Krotz, Ethan Byrd, Ken Miyazaki, Roel Tempelaar

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

Machine-Learning-Guided Insights into Solid-Electrolyte Interphase Conductivity: Are Amorphous Lithium Fluorophosphates the Key?

Peichen Zhong and Kristin A. Persson

Despite decades of study, the identity of the dominant \ce{Li+}-conducting phase within the inorganic SEI of Li-ion batteries remains unresolved. While the mosaic model describes LiF/\ce{Li2O}/\ce{Li2CO3} nanocrystallites within a disordered matrix, these crystalline phases inherently offer limited ionic conductivity. Growing evidence suggests that interfaces, grain boundaries, and amorphous phases may instead host the primary fast-ion pathways. Using diffusion-based generative structure prediction and machine-learning interatomic potentials (MLIPs), we investigate lithium difluorophosphate (\ce{LiPO2F2}), a key mixed-anion decomposition product of phosphorus- and fluorine-containing electrolytes. We identify a stable crystalline polymorph and demonstrate that the amorphous counterpart is conductive, with projected room-temperature $\sigma \approx 0.18$ mS cm$^{-1}$ and $E_\mathrm{a} \approx 0.40$ eV. This enhancement stems from structural disorder flattening the Li site-energy landscape and a low formation energy for Li-interstitial defects, which supplies additional mobile carriers. We propose amorphous mixed-anion Li–P–O–F phases as a promising conducting medium in the SEI, offering a specific target for engineering improved battery interfaces.
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Medical Physics

Radiation enhanced diffusion in cartilages as a physical mechanism underlying radiation treatments of osteoarthritis and related disorders

Diana Shvydka and Victor Karpov

Degradation of joint cartilages can result in osteoarthritis (OA) affecting about 10% of the US population and responsible for significant hospitalization costs. While observations show that low dose radiation treatments (LDRT) bring improvements for a majority of OA patients, the underlying mechanism is not sufficiently understood. Here, we show how the radiation enhanced diffusion (RED) can boost the molecular transport in cartilages promoting cartilage self-healing rendering a mechanism for the observed positive LDRT effects on OA. Along with quantitative estimates for RED, we predict a related phenomenon of the electric charge build up that allows LDRT schedules promoting desirable types of molecular transports dominated by either positive or negative molecular species. Our analyses call upon further experimental verifications and clinical trials with curative rather than palliative intent. In addition to OA applications, our developed approaches can be useful for sports medicine dealing with damage or degeneration of the articular cartilages.
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Sunday 26 October

Instrumentation and Detectors

Sub-microsecond Transformers for Jet Tagging on FPGAs

Lauri Laatu, Chang Sun, Arianna Cox et al. (+7 more)

We present the first sub-microsecond transformer implementation on an FPGA achieving competitive performance for state-of-the-art high-energy physics benchmarks. Transformers have shown exceptional performance on multiple tasks in modern machine learning applications, including jet tagging at the CERN Large Hadron Collider (LHC). However, their computational complexity prohibits use in real-time applications, such as the hardware trigger system of the collider experiments up until now. In this work, we demonstrate the first application of transformers for jet tagging on FPGAs, achieving $\mathcal{O}(100)$ nanosecond latency with superior performance compared to alternative baseline models. We leverage high-granularity quantization and distributed arithmetic optimization to fit the entire transformer model on a single FPGA, achieving the required throughput and latency. Furthermore, we add multi-head attention and linear attention support to hls4ml, making our work accessible to the broader fast machine learning community. This work advances the next-generation trigger systems for the High Luminosity LHC, enabling the use of transformers for real-time applications in high-energy physics and beyond.
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All authors Lauri Laatu, Chang Sun, Arianna Cox, Abhijith Gandrakota, Benedikt Maier, Jennifer Ngadiuba, Zhiqiang Que, Wayne Luk, Maria Spiropulu, Alexander Tapper

Instrumentation and Detectors

Accurate Reporting of Ion Time-of-Flight during HiPIMS with Gated Front-End Mass Spectrometry

Nathan Rodkey, Jyotish Patidar, Kerstin Thorwarth et al. (+1 more)

The quality of high-power impulse magnetron sputtering (HiPIMS) deposited films can often improve through the effective use of metal-ion acceleration, requiring precise measurements of time-of-flight (ToF). These measurements are commonly done using time- and energy-resolved mass spectrometry but require careful consideration of the transit time of ions inside. The transit time is typically calculated by considering the travel length in various parts of the spectrometer (e.g. from orifice to detector), but errors associated with these estimations can lead to nonphysical values in a HiPIMS process (e.g. negative ToFs). Here we report a practical approach to determine ion ToF experimentally, using a bipolar HiPIMS power supply to synchronize a gating pulse to the front-end of a HIDEN Analytical EQP-300 mass spectrometer, placed at the working distance. The ToF is measured by applying a +70 V bias to repel ions, and a 5 us gating pulse of 0 V to accept them. To prevent interference with the HiPIMS plasma, a grounded shield is placed in front of the mass-spec head with a variable slit-opening (0.5-3 mm). The effectiveness of the shielding is verified by Langmuir probe measurements, noting negligible shifts in plasma potential for a DC sputter discharge. The gate is then synchronized to a HiPIMS pulse and data collected at 5 us intervals by adjusting the pulse delay. Measurements of the time-of-flights of Ar+, Al+, Sc+, Y+, and W+ ions are presented; Al+ and Ar+ ions were also compared to ToF calculated using mass spectrometry flight tube equations.
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All authors Nathan Rodkey, Jyotish Patidar, Kerstin Thorwarth, Sebastian Siol

Physics and Society

Ashkin-Teller model with antiferromagnetic four-spin interactions: Interference effect between two conflicting issues

Cook Hyun Kim, Hoyun Choi, Joonsung Jung et al. (+1 more)

Spin systems have emerged as powerful tools for understanding collective phenomena in complex systems. In this work, we investigate the Ashkin–Teller (AT) model on random scale-free networks using mean-field theory, which extends the traditional Ising framework by coupling two spin systems via both pairwise and four-spin interactions. We focus on the previously unexplored antiferromagnetic regime of four-spin coupling, in which strong ordering in one layer actively suppresses the formation of order in the other layer. This mechanism captures, for example, scenarios in social or political systems where a dominant viewpoint on one issue (e.g., economic development) can inhibit consensus on another (e.g., environmental conservation). Our analysis reveals a rich phase diagram with four distinct phases – paramagnetic, Baxter, \langle \sigma \rangle, and antiferromagnetic – and diverse types of phase transitions. Notably, we find that the upper critical degree exponent extends to \lambda_{c2} \approx 9.237, far exceeding the conventional value of \lambda = 5$ observed in ferromagnetic systems. This dramatic shift underscores the enhanced robustness of hub-mediated spin correlations under competitive coupling, leading to asymmetric order parameters between layers and novel phase transition phenomena. These findings offer fundamental insights into systems with competing order parameters and have direct implications for multilayer biological networks, social media ecosystems, and political debates characterized by competing priorities.
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All authors Cook Hyun Kim, Hoyun Choi, Joonsung Jung, B. Kahng

Atomic Physics · Cross-listed from quant-ph

Control of valence-electron motion in Xe cations using the stimulated-Raman-adiabatic-passage technique

Miguel A. Alarcón, Karl Hauser and Nikolay V. Golubev

This work theoretically investigates possibilities of using the Stimulated Raman Adiabatic Passage (STIRAP) and its variants to control a coherent superposition of quantum states. We present a generalization of the so-called fractional STIRAP (f-STIRAP), demonstrating precise control over the mixing ratio of quantum states in the wave packet. In contrast to conventional f-STIRAP, designed to drive a system from an eigenstate into a coherent superposition, our scheme enables arbitrary control over the composition of an already existing superposition state. We demonstrate that an approximate version of this technique – where analytically designed laser pulses with composite envelopes are replaced by simple Gaussian pulses – achieves comparable performance in controlling the dynamics of the wave packet. A limiting case of this scheme, utilizing two pulses with identical Gaussian envelopes and tuned delay and relative phase, is also explored, revealing experimentally accessible pathways for manipulating quantum coherence. We apply our developed techniques to control the ultrafast charge migration in the spin-orbit split ground electronic states of xenon cation via intermediate valence- and core-excited states. Finally, we propose concrete experimental realizations of the developed control schemes in combination with attosecond transient absorption spectroscopy as a method to probe the system.
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Applied Physics

Drone Carry-on Weight and Wind Flow Assessment via Micro-Doppler Analysis

Dmytro Vovchuk, Oleg Torgovitsky, Mykola Khobzei et al. (+11 more)

Remote monitoring of drones has become a global objective due to emerging applications in national security and managing aerial delivery traffic. Despite their relatively small size, drones can carry significant payloads, which require monitoring, especially in cases of unauthorized transportation of dangerous goods. A drone's flight dynamics heavily depend on outdoor wind conditions and the carry-on weight, which affect the tilt angle of a drone's body and the rotation velocity of the blades. A surveillance radar can capture both effects, provided a sufficient signal-to-noise ratio for the received echoes and an adjusted postprocessing detection algorithm. Here, we conduct a systematic study to demonstrate that micro-Doppler analysis enables the disentanglement of the impacts of wind and weight on a hovering drone. The physics behind the effect is related to the flight controller, as the way the drone counteracts weight and wind differs. When the payload is balanced, it imposes an additional load symmetrically on all four rotors, causing them to rotate faster, thereby generating a blade-related micro-Doppler shift at a higher frequency. However, the impact of the wind is different. The wind attempts to displace the drone, and to counteract this, the drone tilts to the side. As a result, the forward and rear rotors rotate at different velocities to maintain the tilt angle of the drone body relative to the airflow direction. This causes the splitting in the micro-Doppler spectra. By performing a set of experiments in a controlled environment, specifically, an anechoic chamber for electromagnetic isolation and a wind tunnel for imposing deterministic wind conditions, we demonstrate that both wind and payload details can be extracted using a simple deterministic algorithm based on branching in the micro-Doppler spectra.
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All authors Dmytro Vovchuk, Oleg Torgovitsky, Mykola Khobzei, Vladyslav Tkach, Sergey Geyman, Anton Kharchevskii, Andrey Sheleg, Toms Salgals, Vjaceslavs Bobrovs, Shai Gizach, Aviel Glam, Niv Haim Mizrahi, Alexander Liberzon, Pavel Ginzburg

Optics · Cross-listed from cond-mat.mes-hall

Deterministic single-photon source with on-chip 5.6 GHz acoustic clock

Alexander S. Kuznetsov, Meysam Saeedi, Zixuan Wang et al. (+2 more)

Scalable solid-state single-photon sources with triggered single-photon emission rates exceeding a few GHz would aid in the wide technological adoption of photonic quantum technologies. We demonstrate triggering of a quantum dot (QD) single photon emission using dynamic Purcell effect induced at a frequency of several GHz by acoustic strain. To this end, InAs QDs are integrated in a hybrid photon-phonon patterned microcavity with engineered optical and acoustic phonon degrees of freedom. The density of optical states is tailored by the lateral confinement of photons in um-sized traps defined lithographically in the microcavity spacer. The single-photon character of the emission from a QD in a trap is confirmed by measuring single-photon statistics. We demonstrate modulation of the QD transition energy in a trap with a frequency up to 14 GHz by monochromatic longitudinal bulk acoustic phonons generated by piezoelectric transducers. For the modulation frequency of 5.6 GHz, corresponding to the acoustic mode of the microcavity, the QD energy is periodically shifted through a spectrally narrow confined photonic mode leading to an appreciable enhancement of the QD emission due to the dynamic Purcell effect. We numerically explored time-evolution of the QD-cavity system under modulation and identified conditions that could enable single-photon rates exceeding 5 GHz. The platform thus enables the implementation of scalable III-V-based single-photon sources with on-chip tunable acoustic clocks with frequencies that can exceed several GHz under continuous wave optical excitation.
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All authors Alexander S. Kuznetsov, Meysam Saeedi, Zixuan Wang, Kevin L. Silverman, Klaus Biermann

Optics

Photon-starved imaging through turbulence at the diffraction limit

Seungman Choi, Peter Menart, Andrew Schramka et al. (+4 more)

Atmospheric turbulence limits the resolution of ground-based imaging through rapidly evolving wavefront distortions. Fast acquisition can effectively freeze turbulence, but the restricted photon budget makes joint scene and wavefront recovery challenging. Here, we introduce Turbulence-Aware Poisson Blind Deconvolution (TAP-BD), which uses optical phase diversity to provide complementary measurements within a short acquisition window and increase wavefront information per detected photon. Poisson denoising and physics-informed optimization translate this information gain into joint recovery of the scene and a shared turbulence wavefront, with phase estimation errors approaching the Cramer–Rao lower bound in simulations. Experiments demonstrate reliable recovery from only a few tens of measurements under strong turbulence, with additional validation under severe photon scarcity. Simulations further show robustness to scintillation and temporal evolution over short acquisition windows. These results support photon-efficient imaging through turbulence, with potential applications in astronomy, remote sensing, and space situational awareness, particularly for time-sensitive observations.
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All authors Seungman Choi, Peter Menart, Andrew Schramka, Shubhankar Jape, Leif Bauer, In-Yong Park, Zubin Jacob

Classical Physics

An extensive search for stable periodic orbits of the equal-mass zero angular momentum three-body problem

Ivan Hristov, Radoslava Hristova and Kiyotaka Tanikawa

A special 2D initial conditions' domain of the equal-mass zero angular momentum planar three-body problem, which has been formerly studied, is analyzed to deepen the knowledge of the stability regions in it. The decay times in the domain are carefully computed. Four stability regions are established. 971 verified initial conditions for linearly stable periodic collisionless orbits are found. Many of these identified initial conditions are new ones. The periodic orbits of each stability region are characterized by a certain pattern in their syzygy sequences. Additional computations show that the orbits found should be considered as candidates for KAM-stable orbits.
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Computational Physics · Cross-listed from math.NA

Surface layers and linearized water waves: a boundary integral equation framework

Travis Askham, Tristan Goodwill, Jeremy G Hoskins et al. (+2 more)

The dynamics of surface waves traveling along the boundary of a liquid medium are changed by the presence of floating plates and membranes, contributing to a number of important phenomena in a wide range of applications. Mathematically, if the fluid is only partly covered by a plate or membrane, the order of derivatives of the surface-boundary conditions jump between regions of the surface. In this work, we consider a general class of problems for infinite depth linearized surface waves in which the plate or membrane has a compact hole or multiple holes. For this class of problems, we describe a general integral equation approach, and for two important examples, the partial membrane and the polynya, we analyze the resulting boundary integral equations. In particular, we show that they are Fredholm second kind and discuss key properties of their solutions. We develop flexible and fast algorithms for discretizing and solving these equations, and demonstrate their robustness and scalability in resolving surface wave phenomena through several numerical examples.
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All authors Travis Askham, Tristan Goodwill, Jeremy G Hoskins, Peter Nekrasov, Manas Rachh

Instrumentation and Detectors

Scintillation of liquid nitrogen

L. Pagani, R. Saldanha, B.M. Loer et al. (+3 more)

Liquid nitrogen is commonly used in cryogenic applications and is a promising medium for the direct immersion cooling of sensors used for nuclear and particle physics experiments. The scintillation properties of gaseous nitrogen are well-documented, but little is known about the scintillation of liquid nitrogen. If present, scintillation light from interactions of ambient radioactivity could produce backgrounds for rare event searches such as the direct detection of dark matter. Using a coincidence-tagged alpha decay, we demonstrate that liquid nitrogen exhibits measurable, albeit very faint, scintillation. Assuming the same scintillation wavelength spectrum as gaseous nitrogen, we estimate a relative scintillation yield of $Y_{\text{LN}}/Y^{\text{STP}}_{\text{GN}} = 0.0142 \pm 0.0005\text{(stat)} \pm 0.0030\text{(sys)}$ with respect to gaseous nitrogen at standard temperature and pressure. Considering the average scintillation yield from alpha decays in gaseous nitrogen, this implies a scintillation yield for alpha decays in liquid nitrogen of $Y_{\text{LN}} = 2.39 \pm 0.56$ photons per MeV. To our knowledge this is the first measurement of scintillation in liquid nitrogen.
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All authors L. Pagani, R. Saldanha, B.M. Loer, G.S. Ortega, R.A. Bunker, B.T. Foust

Optics

Automated control strategy for setting and stabilization of photonic circuits

Jacek Gosciniak

In this paper, we propose the Wheatstone bridge configuration for enabling real-time and closed-loop stabilization and calibration of photonic devices integrated on chip. The measurement of the optical power propagating in a waveguide is achieved by leveraging the photo-thermal resistance variation of one of the resistors that comprise a bridge, which is either part of the waveguide or in close contact with the waveguide. The voltage generated by a monitor is applied through a processing unit to preceding actuators with a view to locking a system at the desired signal level. As all the "resistors" consisting of the Wheatstone bridge are placed on a single material platform in proximity to each other, the bridge is insensitive to temperature variations. Consequently, it functions exclusively as a monitor for the optical power propagating in a waveguide. Due to the high sensitivity of the monitor, automatic re-tuning of the Mach-Zehnder interferometer can be achieved with a recovery time defined by the material properties of the bridge "resistor". The material platform and arrangement can be implemented for both monitoring and activating the actuators, which makes the proposed system an attractive candidate for closed-loop control of optical devices. Furthermore, in contradistinction to the majority of monitors and photodetectors, which provide electrical current as an outcome of measuring an optical signal, the proposed circuit provides voltage, thereby eradicating the necessity to convert current to voltage at a later stage. This serves to firstly streamline the entire circuit and secondly contribute to a substantial diminution in the noise level in the circuit.
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Fluid Dynamics

A Unified Numerical Framework for Turbulent Convection and Phase-Change Dynamics in Coupled Fluid-Porous Systems

Rongfu Guo and Yantao Yang

This work presents a unified numerical framework for simulating incompressible flows within the coupled fluid-porous-medium system and involving heat and solute transport and phase-changing process. A complete set of governing equations is established based on the Darcy-Brinkman equation, the advection-diffusion equations for heat and solute, and a phase field equation describing the evolution of porous medium. Phase-changing process and relevant influences are incorporated as corresponding source terms. A numerical method is then developed to solve the governing equations. Several different types of model problems are simulated with the numerical method. For the incompressible flows inside a coupled fluid-porous-medium system, the channel turbulence over a porous substrate and the thermal convection in a two-layer system are simulated. For the phase-changing flows, the one-dimensional Stefan problem and the two-dimensional flow of pure water freezing are tested. The results agree with the existing simulations. Finally, the full solver is used to simulate the growth of mushy ice during seawater freezing, which can successfully reproduce the experimental results at the exactly same conditions. Therefore, the developed framework provides a versatile and reliable tool for studying complex multiphase, multi-component transport phenomena in fluid-porous-medium systems involving solid-liquid phase change.
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Physics and Society

Larger holes as narrower degree distributions in complex networks

Kiri Kawato and Yukio Hayashi

Although the analysis of loops is not so much because of the complications, it has already been found that heuristically enhancing loops decreases the variance of degree distributions for improving the robustness of connectivity. While many real scale-free networks are known to contain shorter loops such as triangles, it remains to investigate the distributions of longer loops in more wide class of networks. We find a relation between narrower degree distributions and longer loops in investigating the lengths of the shortest loops in various networks with continuously changing degree distributions, including three typical types of realistic scale-free networks, classical Erdös-Rényi random graphs, and regular networks. In particular, we show that narrower degree distributions contain longer shortest loops, as a universal property in a wide class of random networks. We suggest that the robustness of connectivity is enhanced by constructing long loops of O(log N).
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Computational Physics

Using "AI Poincare" to analyze non-linear integrable optics

Lazare Osmanov and Nilanjan Banerjee

This study dives into the applicability of using automated discovery of conserved quantities in dynamical systems relevant to accelerator physics. Specifically, we explore the performance of AI Poincaré in analyzing numerical trajectory data obtained using the McMillan system of non-linear integrable optics. A comprehensive evaluation of the algorithm's performance is conducted through diverse methodologies. These include the analysis of the estimated number of conserved quantities embedded in a dataset and the deviation of interpolated points on the inferred manifold with respect to points in actually in the dataset. the investigation identifies an optimal range of perturbation distances where the underlying manifold extraction algorithm inside AI Poincaré exhibits optimal performance. Additionally, an improved neural network architecture is proposed based on the observed results. Finally, we apply the algorithm to preliminary experimental data from the Integrable Optics Test Accelerator at Fermilab to successfully infer the number of conserved quantities even in the presence of fast decoherence of the measured signal.
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Optics · Cross-listed from quant-ph

Ultrafast Processing of Hyper-Entangled Bell States at the Optical Bandwidth Limit

Netanel P. Yaish, Samata Gokhale and Avi Peer

Bell states embody the most basic form of two-state entanglement and are a key component of quantum protocols of communication and sensing, indicating that high-speed processing of polarization Bell-states is highly desired for quantum technology. Yet, the processing speed of all current protocols is inherently limited by the electronic bandwidth of photo-detectors (Photomultiplier tubes, avalanche photo-diodes, etc.) that can process only $10^{6-7}$ photons/s, whereas standard broadband sources may easily produce $10^{10-14}$ photons/s. Using dual polarization, nonlinear SU(1,1) interferometry as an ultrafast quantum detector of the entangled bi-photons, we demonstrate the complete cycle of processing - generation, manipulation and detection of polarization-entangled Bell states at an ultra-high photon-flux of $\sim\!5\times10^{11}$ photons/s ($\sim\!5$ orders of magnitude higher than standard methods), limited only by the optical bandwidth of the generating source.
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Atmospheric and Oceanic Physics

A Framework for Hybrid Physics-AI Coupled Ocean Models

Laure Zanna, William Gregory, Pavel Perezhogin et al. (+23 more)

Climate simulations, at all grid resolutions, rely on approximations that encapsulate the forcing due to unresolved processes on resolved variables, known as parameterizations. Parameterizations often lead to inaccuracies in climate models, with significant biases in the physics of key climate phenomena. Advances in artificial intelligence (AI) are now directly enabling the learning of unresolved processes from data to improve the physics of climate simulations. Here, we introduce a flexible framework for developing and implementing physics- and scale-aware machine learning parameterizations within climate models. We focus on the ocean and sea-ice components of a state-of-the-art climate model by implementing a spectrum of data-driven parameterizations, ranging from complex deep learning models to more interpretable equation-based models. Our results showcase the viability of AI-driven parameterizations in operational models, advancing the capabilities of a new generation of hybrid simulations, and include prototypes of fully coupled atmosphere-ocean-sea-ice hybrid simulations. The tools developed are open source, accessible, and available to all.
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All authors Laure Zanna, William Gregory, Pavel Perezhogin, Aakash Sane, Cheng Zhang, Alistair Adcroft, Mitch Bushuk, Carlos Fernandez-Granda, Brandon Reichl, Dhruv Balwada, Julius Busecke, William Chapman, Alex Connolly, Danni Du, Kelsey Everard, Fabrizio Falasca, Renaud Falga, David Kamm, Etienne Meunier, Qi Liu, Antoine Nasser, Matthew Pudig, Andrew Shao, Julia L. Simpson, Linus Vogt, Jiarong Wu

History and Philosophy of Physics

Krisenmanagement in Kerntechnischen Notfällen – Eine Evaluaierung Am Beispiel der Nuklearkatastrophe von Fukushima

Elias Koschier

The objective of this pre-scientific paper is to analyze the crisis management during the Fukushima nuclear accident in the year of 2011 and to derive lessons for a safer operation of reactors along with a more resilient crisis management framework. In addition to official reports and subject literature, the conducted methods included interviews with an IAEA safeguard and a political scientist. The central findings were that the accident pointed out deficiencies regarding the independence of the regulatory body and that mismanagement of the available technical resources in conjunction with insufficient communication led to evitable evacuations.
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Optics

Single mode lasing and spectral narrowing in photonic crystal line-defect cavities via spatially selected Bloch modes

Shu-Ning Ding, Ling-Fang Wang, Xiao-Tian Cheng et al. (+10 more)

The demand for high-efficiency and miniaturized on-chip light sources drives continuous innovation in photonic crystal (PhC) microcavity lasers. The presence of slow-light effects in PhC microcavities leads to the mode competition between Bloch modes resulting in multi-mode lasing, which obstructs the dense integration of PhC lasers. Here, we theoretically verify a technical scheme for the single-mode lasing of PhC line-defect-cavity lasers by spatially pumping a certain Bloch mode via optical interference.We demonstrate the capability to select a specific longitudinal mode to lase with a side mode suppression ratio (SMSR) exceeding 30 dB. The interaction between optical interference fringes and the vacuum electromagnetic field inside the PhC cavity improves the linewidth and noise characteristics of lasers. This scheme of Bloch mode selection provides a novel and viable tool for the manipulation of PhC microcavity lasers.
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All authors Shu-Ning Ding, Ling-Fang Wang, Xiao-Tian Cheng, Jia-Wang Yu, Dai-Bao Hou, Yi-Feng Liu, Zhe Feng, Yi Zhao, Yang-Chen Zheng, Xing Lin, Feng Liu, Chen-Hui Li, Chao-Yuan Jin

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

Bidirectional Photoinduced Carrier Transfer in Fluorinated Quasi-2D Perovskites Governing Enhanced Photocurrent Generation

Soumya Halder, Koushik Gayen, Nagendra S. Kamath et al. (+1 more)

Quasi-two-dimensional (quasi-2D) metal halide perovskites exhibit rich phase heterogeneity that profoundly influences light-matter interactions and charge transport. However, the fundamental mechanisms governing carrier transfer across distinct phases remain poorly understood. Here, we demonstrate effective electron-hole separation in fluorinated multilayered quasi-2D perovskite films nominally prepared for three layers, using femtosecond transient absorption spectroscopy. The films are revealed to comprise a heterogeneous phase distribution (with 1, 2, 3 layers and bulk) naturally stacked along the growth direction. Our ultraviolet photoelectron spectroscopy (UPS) measurements, show the type-two band alignment between the small-n (layer number) phases and the bulk. This alignment drives charge separation via both direct and sequential carrier transfer mechanisms, whereby electrons preferentially migrate into the bulk domains while holes accumulate in the small-n layers, extending even to single layer phase-a process only rarely observed in previous studies. The nearly symmetric transfer times of electrons and holes yield an efficient and balanced spatial separation of carriers. Global target analysis employing a carrier transfer model quantitatively reproduces the spectral evolution, providing a rigorous validation of the mechanism. Nonetheless, we found photocurrent enhancement in the diode devices of this quasi-2D perovskite as a consequence of the efficient transfer of photocarriers in the opposite directions. This work delivers a comprehensive picture of interphase charge transfer in fluorinated quasi-2D perovskites and highlights strategies to engineer directional separation pathways for high-performance photovoltaic, optoelectronic, and quantum devices.
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All authors Soumya Halder, Koushik Gayen, Nagendra S. Kamath, Suman Kalyan Pal

Physics and Society

Directionality-induced jamming in multiplex networks

Mateo Bouchet, Alejandro Tejedor, Xiangrong Wang et al. (+1 more)

We study diffusion on multiplex networks with directed interlayer couplings. We demonstrate both numerically and analytically that even with undirected layers, interlayer directionality alone reproduces superdiffusion and the prime regime. We further reveal a new phenomenon, the directionality-induced jamming, whereby directed interlayer links hinder diffusion, fragmenting the system into dynamically disconnected components and preventing convergence to the steady state of the diffusion process. Via an optimization process, we show that this new regime is attainable in both toy models and real-world topologies. These findings underscore the crucial role of interlayer link directionality in shaping the emergent behavior of multiplex systems, with potential implications for the design and control of such systems.
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All authors Mateo Bouchet, Alejandro Tejedor, Xiangrong Wang, Yamir Moreno

Computational Physics

Mesoscopic Modeling of Structure-Transport Relationships in Dense CNT Films Containing Amorphous Carbon

Yvelin Giret, Filippo Federici Canova, Al-Moatasem El-Sayed et al. (+6 more)

Carbon nanotube (CNT) films are widely considered as prospective building blocks for advanced electronic and nanostructured materials. In particular, electrical transport in high-density CNT films results from a complex interplay between network morphology and CNT connectivity, which remains challenging to characterize quantitatively. To identify the structural parameters that govern the electrical current in CNT films, we employed coarse-grained molecular dynamics to construct dense mesoscale CNT film models that include CNTs with different chiralities and lengths. The effects of CNT geometrical features on the film morphologies were quantified by devising a set of structural descriptors and analyzing their mutual correlations. The impact of varying the concentration of amorphous carbon (aC) inclusions on the film structure was assessed. Finally, we employed a nodal analysis framework to compute the electrical current across the networks and correlate the charge transport characteristics to the underlying structural descriptors. The current is found to be enhanced in films that exhibit high curvature and buckling, low bundling, and strong connectivity. We discuss how the presence of aC inclusions modifies these morphological and current characteristics. This work provides a mesoscale modeling framework for modeling structure-transport relationships in dense CNT films and highlights the role of morphological descriptors in guiding the interpretation of electrical transport in complex nanostructured networks.
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All authors Yvelin Giret, Filippo Federici Canova, Al-Moatasem El-Sayed, Thomas R. Durrant, Rahul Sen, Harry Luan, Gennadi Bersuker, Alexander L. Shluger, David Z. Gao