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Physics Physics

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Tuesday 8 September

Optics

Integrated yoctosecond-precision timing detector

Precise timing detection is essential for exploring ultrafast phenomena in fields ranging from free-electron lasers to ultra-high-power laser facilities. However, achieving simultaneous high resolution and large dynamic range remains a fundamental challenge, and state of the art systems are often constrained by their physical size, power requirements, and limited scalability. Here we introduce an integrated dual electro optic sub cycle timing detector (DEST) that overcomes these limitations. In a proof of principle measurement, the device resolves timing jitter as small as 11 yoctoseconds (ys, $10^{-24}$ s) at 1 MHz–equivalent to the transit time of light across two protons–while maintaining an unambiguous measurement range of 6.15 ps and a dynamic range exceeding 155 dB. The core detection unit is miniaturized to chip scale dimensions of 18 mm x 2 mm x 1 mm on a thin film lithium niobate platform, ensuring inherent stability and immunity to environmental disturbances. Moreover, the architecture naturally lends itself to massive parallelization through array integration, with the potential to push timing precision to the sub 10 rontosecond (rs, $10^{-27}$ s) level within a 1 $m^2$ footprint. This combination of extreme sensitivity, wide dynamic range, compact size, and scalability opens new avenues for detecting previously inaccessible weak signals, including those from gravitational waves, quantum vacuum fluctuations, and beyond.
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All authors Jie Yang, Tong Wang, Yulin Shen, Dehui Pan, Zhichao Chen, Ming-Yang Zheng, Bin Wang, Shaobo Fang, Yi Zhang, Ke Zhang, Jiahui Yao, Minghua Chen, Guorong Wu, Xueming Yang, Ming Xin

Optics

Topology of Photonic Time Crystals under Complex Refractive Index Modulation

Photonic time crystals, constructed by periodic modulation of electromagnetic parameters in time, hold unique topological properties. Here, we explore permittivity and conductivity co-modulated PTCs (PCM PTCs) by dynamically tuning permittivity and conductivity simultaneously of the spatially-uniform materials, and discover their distinctive non-Hermitian effects. We find that such PCM PTCs hold a global shift of the Floquet spectrum along the imaginary quasifrequency axis, which controls field amplification and decay in both momentum bands and band gaps. By further considering the temporal interface consisting of two different PCM PTCs, we can unveil the relationship between the emergence of topological edge states and momentum band inversion by analyzing the eigenstates at exceptional points. Moreover, the characteristic of the topology of PCM PTCs can also be captured from the complex Dirac mass. Our work studies the topology of PTCs in complex modulation regime, offering new opportunities for manipulating topological edge states in the time domain.
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All authors Huili Lin, Zhaohui Dong, Xianfeng Chen, Luqi Yuan

Chemical Physics · Cross-listed from quant-ph

Classical Active-Space Hybrid Quantum Subspace Expansion (CASH-QSE): Quantum Corrections without Remeasuring the Classically Calculable Energy

The wave function prepared by a variational quantum eigensolver (VQE) can contain a substantial classically tractable component, yet its energy contribution is sampled on the quantum device. Representing the wave function as a combination of a classical reference and separately prepared quantum states allows the reference energy to be evaluated without quantum sampling. However, near-linear dependence among these components can amplify measurement errors and destabilize the resulting energy estimate. We introduce Classical Active-Space Hybrid Quantum Subspace Expansion (CASH-QSE), which retains a complete-active-space self-consistent field (CASSCF) reference classically and uses occupation structure to construct quantum states exactly orthogonal to the reference and to one another. The energy follows from an ordinary Hermitian eigenvalue problem without overlap measurements, while the same occupation constraints simplify the measured operators. Using full configuration interaction to guide component selection, we test CASH-QSE along H$_2$O and N$_2$ bond-stretching coordinates spanning weakly to strongly correlated regimes. The benchmarks use STO–3G for both molecules and a restricted cc-pVDZ orbital space for H$_2$O. CASH-QSE reaches chemical accuracy while limiting the largest complete measurement circuits to a few hundred all-to-all logical controlled-NOT gates. In favorable cases, it also reduces the idealized final-energy sampling cost by several orders of magnitude relative to VQE with an adaptive derivative-assembled pseudo-Trotter ansatz (ADAPT-VQE).
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Computational Physics · Cross-listed from cs.LG

Learning Metamaterial Eigenmodes with Wavelet-Encoded Fourier Neural Operators

Machine learning surrogates based on neural operators have shown broad applicability in solving forward PDE problems. However, eigenvalue problems, in which an eigenparameter and one of several valid eigenmodes must be simultaneously solved, remain difficult because standard operator learning formulations assume a unique input-output map. This work demonstrates that Fourier Neural Operators (FNOs), combined with wavelet-based encodings of PDE inputs, can learn and predict multiple eigenmodes of the elastic wave equation, corresponding to deformation modes of acoustic waves propagating through arbitrary metamaterial geometries. We provide a mechanistic explanation and experimental evidence for why wavelet encodings are well matched to the dual spatial-spectral structure of the FNO, enabling deterministic mode selection on both continuous-valued and binary-valued geometries within a single model, and for why prediction accuracy varies with geometric discontinuities. For metamaterial design, the resulting surrogate accelerates the simulation stage of the design cycle by three orders of magnitude relative to finite element analysis on a consumer-grade CPU, while preserving high fidelity. These results also carry broader implications for designing input encodings in other multi-mode PDE solvers based on spectral neural operators.
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All authors Han Zhang, Alexander Ogren, Cynthia Rudin, Johann Guilleminot, L. Catherine Brinson

Fluid Dynamics

Coupled thermoacoustic resolvent analysis of a model two-stream coaxial combustor

We derived a resolvent operator to analyze the coupled flame-acoustic effect in a model two-stream coaxial combustor. The theoretical analysis accommodates both the hydrodynamic effect of the active flame and chamber acoustic effect, as well as their coupling effect. Utilizing the coupled thermoacoustic resolvent, we are able to identify the optimal forcing of different mechanisms and their corresponding optimal responses. When this new modeling tool is applied to a two-stream coaxial model combustor, it reveals distinctly different forcing-response characteristics in the coupled system compared to those in a purely hydrodynamic linear system. Acoustic energy peaks, indicative of resonance, are observed. Additionally, it has been found that the acoustic forcing does not maintain a rank-one property. Furthermore, the modes most receptive to the flame-acoustic coupling effect can be identified using a novel sensitivity analysis approach. Interestingly, by employing the coupled thermoacoustic resolvent, we demonstrate that forcing can be designed to negate or counteract perturbations caused by the forcing of another attribute, potentially aiding in the development of effective thermoacoustic control strategies.
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Chemical Physics

Construction of downfolded Hamiltonians from projective transcorrelation

Projective transcorrelation recovers the short-range electron correlation by a similarity transformation with a geminal function $f(r_{12})$, at the cost of an effective Hamiltonian containing a 3-body term. We replace the term by an effective operator of rank at most two, obtained from the two-body cumulant (2C) approximation to the three-particle reduced density matrix. The 2C 3-body energy is written without cumulants, and the effective one- and two-body interactions are derived as its partial derivatives with respect to the reduced density matrices. The truncation is assessed on the atomization and reaction energies of the HEAT set with CCSD(T), and on the CAS-pTC model, whose downfolded Hamiltonian is held on a qubit register with the number of Pauli strings reduced from the sixth power of the orbital count to the fourth.
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Atomic Physics

A Portable Dual-Color Two-Photon Rubidium Optical Frequency Standard

Portable atomic clocks are essential in a wide variety of applications, most notably in the operation of global navigation satellite systems. Existing portable atomic clocks utilizing microwave-based interrogation schemes are now routinely eclipsed by the next generation of atomic frequency standards based on optical interrogation. While optical frequency standards demonstrate greatly improved frequency stability, they have only recently reached a level of technical maturity required to demonstrate this improved performance outside of well curated laboratory environments. Here, we demonstrate a fully autonomous and portable optical frequency standard based on an efficient dual-color excitation of the $5S_{1/2}\rightarrow5D_{5/2}$ two-photon transition in $^{87}$Rb. The standard utilizes a combination of robust, highly developed commercial-off-the-shelf telecommunications technologies and a fully integrated portable optical frequency comb, providing the optical and microwave outputs vital for interfacing with existing electronic systems and infrastructure. The system demonstrates a fractional frequency stability of $1.9\times10^{-13}$ at 1s of integration time, reaching $3.5\times10^{-15}$ at 8000s of integration time without the need for drift removal. This portable demonstrator unit marks a significant achievement in the development of Rb optical atomic frequency standards, and for the deployment of optical atomic frequency standards outside of the laboratory.
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All authors Sarah K. Scholten, Emily Ahern, Clayton Locke, Christopher J. Billington, Nicolas Bourbeau Hébert, Montana Nelligan, Ashby P. Hilton, Rachel F. Offer, Elizaveta Klantsataya, Christopher Perrella, Andre N. Luiten

Monday 7 September

Data Analysis and Statistics · Cross-listed from q-bio.NC

Exploring the robustness of permutation entropy analysis to differentiate between closed-eyes and open-eyes resting states

Electroencephalography (EEG) is a noninvasive technology that is widely used to monitor brain states, and many efforts are focused on developing reliable and efficient data analysis methods for EEG recordings. Here, we apply ordinal analysis to the EEG recording of the resting state of 109 healthy subjects measured in two different conditions: with eyes closed (EC state) or eyes open (EO state). We study the robustness of the temporal permutation entropy ($PE$) and the spatial permutation entropy ($SPE$) with respect to the presence of blinking artifacts in the EO recordings, the duration of the recordings, and the number of EEG channels analyzed. We perform a paired statistical test to assess whether these quantities differ significantly in the EO and EC recordings of the same subject. We find that $PE$ and $SPE$ perform surprisingly well, as they detect significant differences when calculated from the raw signals, even within a short time interval ($PE$) or from a reduced number of electrodes ($SPE$).
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All authors Juan Gancio, Natalia López López, Antonio J. Pons, Giulio Tirabassi, Cristina Masoller

2609.22265 · 7 Sep · This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Gancio, Juan, et al. "Exploring the robustness of permutation entropy analysis to differentiate between closed-eyes and open-eyes resting states." Chaos (2026), and may be found at https://doi.org/10.1063/5.0326211

Plasma Physics

Scalable Production of Lead-212 and Actinium-225 Generators with Fusion Neutrons

Targeted alpha therapy will require a large expansion of ${}^{212}$Pb and ${}^{225}$Ac production. We propose neutron- and photon-driven routes that convert ${}^{230}$Th, ${}^{231}$Pa, ${}^{232}$Th, and ${}^{237}$Np into generator parents ${}^{228}$Th and ${}^{229}$Th. The most direct ${}^{225}$Ac route is ${}^{230}$Th(n,2n)${}^{229}$Th. A 10 MW deuterium-tritium (D-T) neutron source irradiating thorium with a 27% ${}^{230}$Th isotopic fraction accumulates about 250 Ci of ${}^{229}$Th in six months, initially enough for five million ${}^{225}$Ac dose-equivalents per year, and its 7916 yr half-life makes it useful for millennia. This requires only $\sim$2 gigawatt-days of D-T fusion operations. Thermal-neutron irradiation of tens of grams of ${}^{230}$Th produces gram quantities of ${}^{232}$U, a decades-long source of ${}^{228}$Th for millions of ${}^{212}$Pb dose-equivalents per year. Alternate routes proceed through ${}^{231}$Pa: fusion neutrons produce 1 to 2 tonnes of ${}^{231}$Pa per gigawatt-year from ${}^{232}$Th, and a thermal reactor converts up to 0.4 g of ${}^{232}$U per gram of ${}^{231}$Pa. Each gram of stored ${}^{232}$U produces 10 mg (8.2 Ci) of ${}^{228}$Th per year. Subsequent ${}^{228}$Th(n,$\gamma$)${}^{229}$Th converts 0.07 to 0.34 g of ${}^{229}$Th per gram of ${}^{228}$Th. We also analyze the ${}^{237}$Np(n,2n)${}^{236\mathrm{m}}$Np route to ${}^{228}$Th. These pathways scale from kilowatt to megawatt D-T sources and could secure millions of ${}^{212}$Pb and ${}^{225}$Ac dose-equivalents per year.
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Atmospheric and Oceanic Physics

A Physics–ML Multi-Fidelity Strategy for Earth System Model Parameter Optimization: A QG Proof-of-Concept

Earth System Models rely on tunable subgrid-scale parameterizations, but optimizing these parameters is computationally expensive, particularly when nonlinear interactions require many simulations. We present a hybrid Physics-ML multi-fidelity framework that combines Green's Function Optimization (GFO) with Gaussian Process or Neural Network surrogate optimization. Using a quasi-geostrophic turbulence model, GFO first ranks parameter sensitivities in normalized coordinates and selects a reduced active subset. Nonlinear surrogates then explore this subset using inexpensive 30-day simulations before refining promising candidates with 180-day simulations. Across seven strategies and a 35-member ensemble, GFO-MultiGP and GFO-MultiNN achieved mean improvements of 64.6 percent and 65.2 percent, respectively, while reaching practical saturation after 3,060 and 2,520 simulation-days. The corresponding standalone GP and NN achieved 61.1 percent and 42.0 percent improvements and required 7,740 and 6,660 simulation-days. These results demonstrate an end-to-end sample-efficiency advantage for the tested hybrid pipelines. Because screening, dimensionality reduction, initialization, and fidelity scheduling change simultaneously, their individual contributions are not isolated.
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All authors Abdullah A. Fahad, Manmeet Singh, Donifan Barahona, Anton Darmenov, Andrea Molod

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

A thermomechanical framework for strongly nonlocal continua

The paper presents a consistent thermomechanical framework for strongly nonlocal continua, a type of generalized media in which a material's response at a point depends on deformation and temperature gradients within its neighborhood. Such dependence is responsible for localization phenomena having an intrinsic size, and nonlocal modeling also serves as a practical regularization tool to prevent mesh dependence. Nonlocality is of the integral type, using a kernel function that gives the relative influence of neighboring points on a central point. The paper develops three sources of nonlocality: (1) nonlocal momentum balance equations; (2) nonlocal conservation laws (including the first and second laws of thermodynamics); and (3) a material's nonlocal constitutive structure. Balance equations are derived using the principle of virtual power, permitting non-smooth force and displacement fields and non-smooth boundary surfaces with indistinct normal directions. The balance equations differ from those of classical local continua. Conservation laws also differ from those of local continua, with the mechanical power and heating at a point being averaged over its neighborhood. These laws are developed for processes that are sufficiently slow to minimize additional meso-scale kinetic energy due to internal turbulence. Stress, entropy, and dissipative forces are obtained as averaged derivatives of the free energy function with respect to strain, temperature, and internal variables. An example is presented of a stretched elastoplastic bar with a small defect, and nonlocality is shown to impart a characteristic size to the deformation pattern.
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Computational Physics · Cross-listed from cond-mat.stat-mech

Diagonal Pair Coulomb Density Matrix on a Sphere: a numerical study

We tabulate, on the diagonal, the $n$th power of the primitive approximation for the pair Coulomb density matrix on a sphere, with up to $n=5$, and we discuss its behavior at particles contact as $n$ grows. Our results show that even on a curved surface quantum statistical physics is fundamentally different from its classical counterpart. If in the latter one needs to artificially introduce a regularization of the divergent attractive Coulomb potential preventing particles contact, for example with a hard core, in the former this is not necessary.
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General Physics

RSD constraints on power-law $f(Q)$ gravity using Barboza-Alcaniz and Jassal-Bagla-Padmanabhan parametrizations

We investigate the late-time accelerated expansion of the Universe in power-law $f(Q)$ gravity, $f(Q) = Q + 6\gamma H_0^2 \left(\frac{Q}{Q_0}\right)^n$, combined with two dynamical dark energy parametrizations, Barboza-Alcaniz (BA) and Jassal-Bagla-Padmanabhan (JBP), which allow a smooth evolution of the equation of state beyond the standard constant $\omega$ assumption. We derive analytical expressions for the Hubble parameter and the dark energy density, and constrain the model using Pantheon$^+$ Type Ia Supernovae, DESI DR2 Baryon Acoustic Oscillations, and Cosmic Chronometers. Going beyond purely geometrical probes, we incorporate Redshift Space Distortion (RSD) measurements to test the growth of cosmic structures and distinguish modified gravity from General Relativity through the effective Newton's constant. Both parametrizations reproduce the observed late-time acceleration and remain consistent with growth data, with only mild deviations from $\Lambda$CDM over low and intermediate redshifts. Notably, both configurations yield $G_{\rm eff} < G$, indicating suppressed growth of matter perturbations. These results establish power-law $f(Q)$ gravity with BA and JBP parametrizations as a viable and versatile alternative to $\Lambda$CDM across both background and perturbative regimes.
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All authors Chaymae karam, Dalale Mhamdi, Taoufik Ouali, Rachid Ahl Laamara, Mohamed Bennai

History and Philosophy of Physics · Cross-listed from q-bio.NC

Revisiting the Aerts-Broekaert-Smets quantum model of the liar paradox

The quantum model of the two-sentence liar paradox proposed by Aerts, Broekaert, and Smets is an early example of the use of quantum formalism to describe cognitive dynamics. Our reconstruction is primarily pedagogical in intent, but it also leads to a number of clarifications, and to some new observations, concerning the structure of the model. Rewriting the model in Dirac notation, we make explicit the distinction between truth values originating from a decision and from semantic inference, and show that the associated enlargement of the one-sentence state space corresponds to a factorization with respect to which the non-paradoxical configurations are separable while the genuine liar state is entangled. We also derive the Hamiltonian generating the four-state cyclic evolution, express it in compact operator form, and give the resulting transition probabilities in closed form. We emphasize that the liar cycle admits a unitarily equivalent representation in the four-dimensional truth-only space, where the unmeasured liar state is separable, so the dimensional enlargement is not required by the unitary part of the dynamics; it is required, however, by the measurement structure. The enlargement is also required by the dynamics as soon as revision processes are admitted, in which states with identical truth content but different origins have different successors, the origin degree of freedom then acting as a minimal form of cognitive memory. We conclude by discussing the possible relationship between the model and more general deliberative processes.
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Physics and Society · Cross-listed from cs.AI

Adaptive Entangled Neurons in the Brain and Natural Intelligence Simulations for Artificial General Intelligence

Understanding the brain's mechanisms is crucial in neuroscience, particularly for simulating natural intelligence and advancing artificial general intelligence (AGI). Liu et al. (2024) and Deco et al. (2025) propose that quantum entanglement may underlie the synchronization of millions of neurons, introducing the Liu-Chen-Ao (LCA) hypothesis of entangled nerve fibers. However, directly testing this idea remains challenging. Here we employ a nonlocal many-body wave equation, introducing a generalized probability-wave framework to model collective behaviors among adaptive, interacting agents, particles, or neurons. This approach enables testable eigenmodes, offering an indirect means of examining the LCA hypothesis by observing patterns in collective trading behaviors. These patterns, rooted in behavioral psychology, are thought to mirror the internal brain's decision-making and underlying mechanisms. Our analysis of Chinese intraday stock market data shows that adaptive entangled game modes explain 82%-94% of decision patterns, sharply contrasting neoclassical finance predictions assuming independent rational agents. Additionally, 2-12% of actions adapt to news, events, and environmental changes, marked by rapid equilibrium shifts, while truly independent behaviors make up less than 5%. These results empirically support the LCA hypothesis and underscore the need to simulate the brain's mechanisms and generate adaptive, entangled modules for AGI. They also expose the shortcomings of conventional artificial neural networks (ANNs) that depend on vast, opaque parameters. By combining ANN-based AI with probability-wave-based entangled brain simulations, machine learning enables the creation of human-like processing units (HPUs). Such HPUs promise more efficient and robust AGI, particularly for embodied intelligence and robotics.
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All authors Haochen Li, Xinshuai Guo, Jingdong Ouyang, Wei Zhang, Leilei Shi

Computational Physics · Cross-listed from quant-ph

From Bits to Qubits: The Theory and Practice of Quantum Data Encoding

Encoding classical data into quantum systems is a foundational step in the execution of nearly all quantum algorithms, and a critical bottleneck in realizing practical quantum advantage. This review provides a comprehensive account of the concepts, algorithms, and practical considerations associated with quantum data encoding. We trace the development from its early conceptual foundations to recent advances, considering commonly used access models, such as quantum state preparation, unitary synthesis, QRAM and block encoding. We survey the circuit size, depth, space-time tradeoffs, as well as non-Clifford resources required for fault-tolerant implementation. We also discuss the roles of different access models in quantum algorithms. Special attention is given to structured data, such as sparse data, Boolean functions and data represented by tensor networks. This review bridges theory and applications, serving both as a pedagogical guide for newcomers and as a reference for active researchers. We also highlight the pivotal role of quantum data encoding in quantum computing and provide insights into future directions that will enable quantum advantage.
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All authors Xiao-Ming Zhang, Arthur G. Rattew, Bujiao Wu, Georgios Styliaris, Xiaoming Sun, Bálint Koczor, Xiao Yuan

Plasma Physics

Runaway electron control by self-excited waves

Runaway-electron avalanches in tokamak plasmas can be limited by kinetic instabilities driven by the non-Maxwellian runaway distribution. We formulate a reduced model for the quasi-steady state in which the total plasma current and bulk electron temperature are prescribed, while the inductive electric field is determined self-consistently from the partition between Ohmic bulk current and runaway-electron current. Because the wave growth time is short compared with the current-decay time, we consider a marginal-stability regime, in which whistler-wave drive by the runaway electrons balances collisional damping. The resulting states separate into three regimes: a subcritical Ohmic regime without an avalanche, an avalanche regime in which runaway growth relaxes the inductive field to the avalanche threshold, and an instability-regulated regime in which self-excited whistler waves enhance momentum-space diffusion and limit the runaway current. In the instability-regulated regime, the whistler wave spectrum forms a narrow ridge, and low-energy runaway electrons carry most of the runaway current.
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Optics · Cross-listed from quant-ph

Quantum magnonics with engineered dissipative and coherent interactions

Cavity magnonics is moving beyond the conventional paradigm of coherent spin–photon hybridization toward the controlled engineering of dissipative and coherent interactions, Floquet dynamics, and quantum fluctuations. This Perspective examines how these ingredients reshape collective dynamics and open new avenues for quantum state engineering, transport, and sensing. We discuss the role of dissipative coupling and anti-$\mathcal{PT}$ symmetry in enabling long-lived collective modes and enhanced spectral response, and highlight Floquet engineering as a means of engineering nonreciprocal transport and phase-controlled interactions. We then review recent progress in quantum magnonics, ranging from squeezed and entangled magnon states, including the squeezing of thermal magnons, to prospective schemes for preparing magnonic Schrödinger-cat states. We also discuss how parametric driving and active gain strongly modify hybrid susceptibilities and amplify magnon–photon response. These advances expand the scope of cavity magnonics beyond conventional polariton physics, establishing it as a versatile platform for sensing, transduction, spin transport, and hybrid quantum technologies.
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Applied Physics

Capacitance of Undoped Thin-Film Diodes

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

Medical Physics

Reducing Hydrocephalus Shunt Revision Rates: A Computational Fluid Dynamics Study on Catheter Hole Design

Proximal shunt obstruction is the leading cause of ventriculoperitoneal (VP) shunt failure in pediatric hydrocephalus and is closely tied to the near-wall shear environment at drainage holes. We used computational fluid dynamics (COMSOL) to decouple local wall-shear-stress (WSS) control via catheter-tip geometry from global drainage control via a valve opening. A cylindrical ventricle domain with Newtonian CSF ($\rho$ = 1000 kg/m$^3$, $\mu$ = 1 mPa$\cdot$s) and $\Delta P \approx$ 10 mmHg was solved under laminar Navier-Stokes flow while sweeping distal hole spacing, hole count/diameter, and a simplified valve constriction. Mesh-independence was achieved (minimum element size $\approx$ 0.021 mm; distal-hole velocity converged to $\approx$ 1.18$\times10^{-3}$ m/s). Perpendicular separation of the two most distal holes increased total outflow by $\approx$ 22% (2 mm vs 0.5 mm) and raised distal lateral-wall WSS by $\approx$ 19%, whereas longitudinal shifts of upstream holes produced only small changes. A valve opening near 0.166-0.17 mm set system drainage to $\approx$ 20 mL/h across geometries, indicating capacity is valve-limited while local WSS is geometry-controlled. The selected tip uses two conical holes (0.5 mm ID) in four rows with 1.4 mm spacing, concentrating WSS at the distal lateral walls, the surfaces where obstruction occurs, without exceeding clinical drainage targets. These findings yield design rules: prioritize distal-pair spacing, reduce hole count with smaller conical openings to elevate protective WSS, and regulate outflow with the valve. The framework provides a clear path to benchtop validation, long-term adhesion assays under mapped WSS, and anatomically realistic CFD.
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Biological Physics

Transcription rate dynamics and RNA copy number noise: General relations and data-driven predictions

Stochastic models of gene expression typically begin with a microscopic model of transcription and propagate its statistics to the RNA distribution. Here we develop a doubly stochastic framework in which RNA production is Poisson conditional on a time-varying transcription rate $\lambda(t)$. For RNA lifetimes drawn independently from an arbitrary finite-mean distribution, we derive the RNA Fano factor in terms of the lifetime survival function and the autocovariance of $\lambda(t)$. For a Poisson degradation process with rate $\mu$, the survival kernel provides an exponential temporal filter, and the result depends only on the mean, variance, and normalized autocorrelation of $\lambda(t)$. These quantities may be calculated from an explicit rate model or, under ergodicity and adequate sampling, estimated from a sufficiently long rate trajectory. We validate the data-driven estimator using simulated transcription-rate trajectories, without supplying the known autocorrelation to the estimator. We also obtain exact analytical results for transcription-rate dynamics modeled by a discrete M/M/1 process and by drift-diffusion with reflecting, periodic, or first-passage-reset boundaries, and verify each result by direct simulation of the coupled transcription-rate and RNA copy-number processes.
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All authors Amara McCune, Ido Golding, Shlomi Reuveni, Sarah Kostinski

Optics

Beam angle-locked loop in laser interferometry

Maintaining precise beam coalignment is essential in laser interferometry, particularly for interspacecraft missions where angular misalignments introduce tilt-to-length coupling noise and risk complete link failure. This work presents a comprehensive theoretical and experimental framework for the beam angle-locked loop, which maintains coalignment between two interfering beams. Minute angular misalignments are detected via differential wavefront-sensing signals, which are used as the error signal for feedback control. A detailed linear control model incorporating an angle detector, a digital filter, a proportional-integral-double-integral servo, a digital-to-analog converter, and a beam-steering mechanism is developed. Using loop transfer functions, we establish a noise-propagation model that quantifies the contributions of individual components to both out-of-loop and in-loop angle errors. The analytical results are experimentally validated using a transponder-based interferometric link spanning two optical benches, with a hexapod simulating spacecraft attitude jitter. The measured transfer functions and coalignment performance agree well with theoretical predictions, yielding a pointing stability better than 10 urad$/\sqrt{\text{Hz}}$ between 0.2 mHz and 1 Hz. Furthermore, a loop-optimization strategy is demonstrated to minimize angle misalignment within a target frequency band by tuning the servo gain, without requiring hardware modifications. This validated framework provides a reliable architecture for designing and optimizing active beam alignment in laser interferometry.
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All authors Daikang Wei, Christoph Bode, Vitali Müller, Juan José Esteban Delgado, Gerhard Heinzel

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

Substrate-induced crystallisation in polymers: Exceptional impact of prefreezing versus heterogeneous nucleation on kinetics and morphology

Crystallisation of liquids often occurs at solid surfaces, via heterogeneous nucleation or prefreezing. Understanding this process is crucial for controlling crystal morphology in thin films and developing efficient nucleating agents - especially for polymers, typically processed in a molten state. However, the efficiency of nucleation and prefreezing with respect to crystallisation kinetics and semicrystalline polymer morphology has not been well studied and remains unclear. Here, we address this challenge by conducting a systematic study of substrate-induced crystallisation in dewetted droplets of the model polymer poly($\varepsilon$-caprolactone) (PCL) on various crystalline and amorphous substrates. Using polarized light optical microscopy, droplet crystallisation temperature was monitored and varied across the substrates, revealing three scenarios: close-to-homogeneous nucleation on glass and silicon; heterogeneous nucleation on ordered and disordered carbon-rich substrates; and prefreezing on graphene. The temperature-dependent nucleation rate was analysed and found to obey classical nucleation theory for all systems except PCL on graphene, where it diverges as all the droplets crystallise simultaneously. The highest in- and out-of-plane PCL crystal orientation is found on graphene, where the epitaxially grown lamellae extend vertically over several hundred nanometres. These results demonstrate that prefreezing has a superior influence on crystallisation kinetics and crystal morphology, making prefreezing substrates perfect nucleating agents.
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Optics · Cross-listed from cond-mat.quant-gas

Limit Cycles in a Photonic Dimer with Tuneable Non-Hermitian Interactions

Interactions govern the emergence of collective behaviour in classical and quantum many-body systems. While conservative interactions are well known to generate nonlinear phenomena ranging from self-trapping to pattern formation, it remains largely unexplored whether purely dissipative – i.e., non-Hermitian – interactions can give rise to similarly rich dynamics and nontrivial system states. Here, we experimentally realise tuneable non-Hermitian interactions in two coupled condensates of light confined within a dye-filled double-well microcavity. Local coupling to molecular reservoirs generates the effective dissipative photon interactions. We show that the interplay between coherent tunnelling and interactions stabilises limit-cycle oscillations, a hallmark of nonlinear dynamics traditionally associated with Hermitian nonlinearities. By tuning the reservoir coupling, we map out the dynamical phase diagram comprising stable fixed points and limit cycles, thereby demonstrating direct control over the interaction strength. Our experimentally validated model reveals both supercritical and subcritical Hopf bifurcations, giving rise to hysteresis, bistability and excitability. These results validate dissipative interactions as a mechanism for organising collective nonlinear dynamics in driven-dissipative systems and pave the way towards exploring nonequilibrium many-body physics through controlled dissipation.
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All authors Kevin J. H. Peters, Peter Schnorrenberg, Daniel Ehrmanntraut, Nikolas Longen, Julian Schmitt

Fluid Dynamics · Cross-listed from cs.LG

Structured Extrema Errors in Classical Surrogates for Viscous Burgers: A Physics-Consistent Interpretation

We study the local errors of classical machine-learning surrogate models, which approximate the time evolution of the one-dimensional viscous Burgers equation. Four models are compared on the same prediction task, using the spatial grid values directly: radial basis function (RBF) kernel ridge regression (KRR), linear Ridge, ExtraTrees, and Random Forests. Across all four models, the one-step residual, defined here as the true value minus the predicted value at each grid point, forms clear curved branches near predicted maxima and minima. A more detailed analysis of KRR shows that these errors are much more strongly related to the second spatial derivative, which measures local curvature, than to the first spatial derivative. Near a smooth extremum, predicted value and curvature form a local two-branch fold. Under our local curvature-based model of the residual, this fold predicts a leading-order near-parabolic relation between predicted value and residual. This geometric result motivates a direct test of the Burgers advection (transport) and diffusion (smoothing) terms. For KRR and Ridge, regression tests on held-out trajectories, a control that breaks the spatial alignment of the diffusion term, and a spectral test of high-frequency content are consistent with insufficient viscous smoothing at moderate and high viscosity. In this case, the surrogate retains more small-scale structure than the true future state. The same physical explanation is much weaker for the tree models. Finally, a correction that uses only predicted quantities reduces both one-step error and error during recursive rollout, where each prediction is used as the next input.
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Optics

Spectro-temporal shaping of broadband optical wavepackets via programmable on-chip photonics

The ability to precisely shape the properties of light over multiple degrees of freedom constitutes the foundation of modern photonic architectures. Broadband sources with addressable spectro-temporal content are for instance critical for applications spanning biomedical imaging, material processing, lidar, and ultrafast spectroscopy, but also key enabling technologies in quantum information processing, high-capacity communications, and optical computing. Yet, flexible and adjustable spectro-temporal shaping so far remains a significant challenge, as it requires the simultaneous manipulation of both frequency and temporal domains across broad spectral bandwidths and extended timescales, from femtoseconds to nanoseconds. Importantly, conventional approaches to spectro-temporal processing typically rely on bulky and complex optical systems that lack scalability and flexibility, ultimately hampering their utility for applications requiring addressable multiphotonic processes. Here, we present a framework for spectro-temporal wavepacket control over a broad bandwidth, merging programmable integrated photonics with high-speed optical characterization. Leveraging machine leaning for tailoring nonlinear pulse propagation, we experimentally report scalable and on-demand shaping of broadband ultrafast pulse patterns. We demonstrate the efficacy of our method through reconfigurable power across 400 nm bandwidth with picosecond resolution, with promises for applications where precise control over light is paramount, in particular those needing versatile and controllable multiphoton excitations.
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All authors Bruno P. Chaves, Jérémy Saucourt, Van Thuy Hoang, Alexis Bougaud, Yassin Boussafa, Erwan Ferrandon, Sai T. Chu, Brent E. Little, David J. Moss, Roberto Morandotti, Vincent Couderc, Benjamin Wetzel

Instrumentation and Detectors · Cross-listed from hep-ex

Solid-state nuclear magnetic resonance search for axion-like dark matter with broadband SQUID magnetometry

We report the results of an experimental search for ultralight axion-like dark matter in the mass ranges 19.5–20.5 and 21.5–22 neV. The Cosmic Axion Spin Precession Experiment-electric probes the axion-nuclear electric dipole moment coupling. We perform solid-state nuclear magnetic resonance on $^{207}$Pb spin ensembles which reside in a polarized ferroelectric crystal. The background axion-like dark matter field induces an oscillating torque on the $^{207}$Pb spins via the electric dipole moment coupling $g_{d}$. The experiment is calibrated with pulsed magnetic resonance measurements covering two frequency bands (4.6–5.0 and 5.2–5.3 MHz) that correspond to the axion Compton frequencies associated with the identified axion mass ranges. By sweeping the leading magnetic field applied to the sample, we are able to detect the $^{207}$Pb nuclear magnetic resonance in these frequency ranges using a superconducting quantum interference device, inductively coupled to the sample with a broadband circuit. We establish the upper bounds $|g_{d}| < 4\times 10^{-4}$ GeV$^{-2}$ with 95% confidence in these frequency bands. Our results demonstrate the detection and small-tip angle calibration of low-field $^{207}$Pb nuclear magnetic resonance, allowing for sensitivity to axion-like dark matter in the nanoelectron-volt axion mass range.
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All authors Andrew J. Winter, János Ádám, Deniz Aybas, Dmitry Budker, Derek F. Jackson Kimball, Surjeet Rajendran, Arne Wickenbrock, Alexander O. Sushkov

Physics and Society

Latent geometry organizes higher-order interactions

Higher-order structures offer a natural representation of complex systems that involve interactions between groups of different sizes. A widespread feature of their higher-order structure is nestedness, whereby interactions involving smaller groups are contained within larger ones. Yet, why interactions of different orders organise into nested structures remains largely unexplained. Here, we introduce an analytically tractable geometric model of higher-order networks in which a single latent geometric space couples interactions across orders, leading to the spontaneous emergence of nestedness. We show analytically and numerically that nestedness undergoes a transition between a nested geometric regime, where it remains finite in the thermodynamic limit, and a regime where it vanishes with system size. In this regime, we uncover a weakly geometric range characterized by an anomalously slow finite-size decay, allowing substantial nestedness to persist in finite systems even when its asymptotic value vanishes. Finally, with a single geometric coupling parameter, the model reproduces the nestedness profiles observed in real-world hypergraphs across different domains. Our results reveal latent geometry as a simple organising principle underlying the nested organisation of higher-order interactions.
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All authors Berné L. Nortier, Jasper van der Kolk, Robert Jankowski, Simon Dobson, M. Ángeles Serrano, Federico Battiston, Marián Boguñá

Classical Physics

Conformal Symmetry and Planck's Thermal Radiation in Classical Physics

Thermal radiation is discussed for a classical scalar field. Dilation and acceleration appear in conformal symmetry, and so are treated in connection with zero-point radiation and equilibrium thermal radiation. Classical zero-point radiation is completely invariant under dilation in a inertial frame. However, in a Rindler frame, zero-point radiation takes a different form which is related to Planck's thermal spectrum with temperature T related to acceleration. Traditionally, zero-point radiation is said to take a thermal (Unruh) form in a Rindler frame. However, the classical viewpoint indicates that zero-point radiation in a Rindler frame requires a divergent frequency spectrum and so is not thermal radiation. The Unruh form suggests an additional classical thermal spectrum satisfying the Stefan-Boltzmann relation.
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Applied Physics

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

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