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Physics Physics

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Monday 10 August

Instrumentation and Detectors

Openable Force-Balanced Halbach Magnets: From Fibonacci Sphere Simulations to Icosahedral Realizations

Ingo Rehberg, Helmut Soltner and Peter Blümler

A long-standing goal in magnet design is to completely surround a volume of highly homogeneous magnetic field with permanent magnets while maintaining practical access to that volume. In this work, we present a theoretical and experimental investigation of mechanically accessible spherical magnets in Halbach configuration that can be opened with minimal or vanishing force. Focusing on dipolar Halbach spheres composed of discrete magnetic subunits, we derive conditions for force-free opening along specific cutting planes. These conditions define a continuous set of geometries for which tensile magnetic forces cancel, leaving only shear components, enabling mechanically effortless opening. The theoretical predictions are validated experimentally using icosahedral approximations of the Halbach sphere, for which both opening forces and magnetic field properties are measured. The results demonstrate that excellent field homogeneity can be preserved while reducing opening forces by orders of magnitude. Although discussed in detail for the dipolar case, the theoretical framework is general and applicable to higher-order multipole Halbach systems. Finally, the concepts are extended to spherocylindrical Halbach configurations, highlighting their potential for large-volume, highly homogeneous, and mechanically accessible permanent-magnet systems for magnetic resonance
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Applied Physics · Cross-listed from cond-mat.mes-hall

Size-Dependent Band-Tail Localization in Oxide Semiconductors Revealed by Direct Density-of-States Mapping

Chang Niu, Kisoo Nam, Aravindh Shankar et al. (+5 more)

Disorder-induced localization is expected to become increasingly important as amorphous oxide semiconductor transistors are scaled toward low-dimensional channels, yet the electronic states responsible for this transport regime remain difficult to resolve experimentally. Here, we use a lock-in-based electric-field penetration technique to directly map the effective density of states (DOS) in In-based oxide semiconductor thin-film transistors (TFTs). The extracted quantum capacitance, carrier density, and chemical potential reveal a disorder-dominated transport regime in which band-tail states are not merely passive traps, but become screening-active and partially transport-active. Geometry-dependent DOS mapping shows an exponential suppression of the effective DOS with channel length, demonstrating size-dependent band-tail localization and providing a microscopic origin for a distinct localization-induced threshold-voltage roll-off mechanism. Temperature-dependent measurements show that the disorder-dominated DOS is strongly suppressed at low temperatures, while extended diffusive states remain nearly unchanged, confirming the localization origin. By tuning film thickness, O2 annealing, and In/Ga/Zn composition, we further demonstrate systematic suppression of disorder and effective-DOS localization. This work establishes direct DOS mapping as a device-level probe of localization physics and provides a pathway for engineering disorder in low-dimensional oxide semiconductor electronics.
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All authors Chang Niu, Kisoo Nam, Aravindh Shankar, Jian-Yu Lin, Sanjeev Khare, Sumi Lee, Pramey Upadhyaya, Peide D. Ye

Optics

A Collective Propagation Law of Optical Vortex Constellations and Longitudinal Sensing

Niladri Modak, Rafael F. Barros, Marco Ornigotti et al. (+1 more)

Optical vortices are ubiquitous phenomena naturally appearing in wave physics, yet higher-order charges inherently split into constellations of lowest-order singularities at the smallest deviation from an ideal situation. While these constellations are common phenomena in real-world scenarios, characterizing their longitudinal evolution typically relies on exhaustive full-field descriptions or the ambiguous, sequential tracking of individual singularities. Here, we reveal and experimentally demonstrate a simple deterministic law describing the paraxial longitudinal propagation of an arbitrary constellation of optical vortices in standard Gaussian backgrounds. By mapping the constituting singularity coordinates to their elementary symmetric polynomials (ESPs), we capture the holistic evolution of the constellation during propagation, completely bypassing the practical need to sequentially track indistinguishable vortices. We further show that such complex ESPs provide a useful metrological tool for the estimation of longitudinal displacements. Our results reveal a previously unrecognized compact description of collective vortex dynamics, introducing a new route to longitudinal sensing through singularimetry.
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All authors Niladri Modak, Rafael F. Barros, Marco Ornigotti, Robert Fickler

Atomic Physics

Stroboscopic Raman Spectroscopy of Atom Optics in Quasi-Bragg Regime

Joel Gomes Baptista, Louis Pagot, Sébastien Merlet et al. (+2 more)

Quasi-Bragg regime is a good compromise for large-momentum-transfer atom interferometry, allowing for scaling up the interferometric area, while constraining the population of unwanted states. Separation of momentum states via standard time of flight methods, however, can be challenging when using laser-cooled atoms, rather than ultracold atoms with sub-recoil velocity distribution. To overcome this limit, we use Raman spectroscopy for stroboscopic sampling of the atomic state evolution in momentum space during the interrogating laser pulses. We quantitatively characterize atom optics employing two-photon (2___k) and multi-photon (6___k) Bragg transitions, the latter being optionally enhanced with optimal control protocol. We closely match the observed dynamics of the atomic state with simulations. Finally, we perform momentum spectroscopy of the output states in a 6___k Bragg gravimeter.
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All authors Joel Gomes Baptista, Louis Pagot, Sébastien Merlet, Leonid Sidorenkov, Franck Pereira Dos Santos

Optics · Cross-listed from quant-ph

Evidence for Counterfactual Violation of Local Conservation Laws in Quantum Events

Patrick Cameron, Francesco Di Colandrea, Filippo Cardano et al. (+1 more)

Physical conservation laws, such as those of energy and momentum, are generally believed to hold exactly and locally in spacetime, including in quantum phenomena. Yet Aharonov, Popescu, and Rohrlich (APR) recently argued, on the basis of a thought experiment, that individual quantum events, unlike ensemble averages, may occasionally violate local conservation laws. Their argument relies on the wave phenomenon known as "superoscillations", which APR themselves discovered more than 30 years ago. Here we provide experimental evidence for such a violation. We extract photons from a small superoscillatory region near the core of an optical vortex and show that their mean transverse momentum is statistically incompatible with a general bound implied by local momentum conservation. The derivation of this bound requires only the theoretically well-supported assumption that the extraction mechanism does not alter the photons' mean transverse momentum. We also detect photons with high transverse momentum at a rate significantly exceeding that predicted by a model assuming local momentum conservation. Because this violation can be established only counterfactually and through postselection, it does not conflict with relativistic causality. Our results may represent the first example of a distinct form of quantum nonlocality that does not explicitly rely on entanglement.
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All authors Patrick Cameron, Francesco Di Colandrea, Filippo Cardano, Lorenzo Marrucci

Optics

High-speed volumetric amplitude-spectrum dynamic optical coherence tomography by neural network with multi-burst scanning

Yusong Liu, Ibrahim Abd El-Sadek, Atsuko Furukawa et al. (+3 more)

Dynamic optical coherence tomography (DOCT) enables label-free, three-dimensional (3D) assessment of tissue dynamics. However, it suffers from long acquisition times because conventional time-spectrum DOCT requires hundreds of repeated OCT frames per location. Here we present a neural network (NN) framework integrated with a non-uniform-time scanning protocol (multi-burst scan) to accelerate amplitude-spectrum DOCT (AS-DOCT). Combining 3D convolutional and long-short term memory (LSTM) layers with dual inputs (the temporal OCT sequence and its pseudo-amplitude spectrum), the model generates AS-DOCT images from only 16 frames per location. Validated on 29 cancer spheroids, the proposed method resolved distinct functional domain structures with high fidelity (structural similarity index metric (SSIM) > 0.8) and enabled full volumetric AS-DOCT acquisition in 26.2 seconds. This method will enable high-throughput 3D dynamic tissue screening.
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All authors Yusong Liu, Ibrahim Abd El-Sadek, Atsuko Furukawa, Rion Morishita, Satoshi Matsusaka, Yoshiaki Yasuno

Classical Physics · Cross-listed from math-ph

Theoretical analysis of the maximum range of a projectile released from a pendulum

Ken Yamamoto

The motion of a projectile released from a simple pendulum is analyzed, with particular emphasis on investigating the optimal release angle that maximizes the horizontal range and the corresponding maximum range. This system serves as a simplified model of the Tarzan jump problem. Using simple analytical methods, the optimal release angle is shown to be characterized by a cubic equation and to increase with the initial velocity. In addition, asymptotic expressions for both the optimal angle and maximum range are derived in the limits of low and high initial velocity.
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Atmospheric and Oceanic Physics

3D Modeling of a Tethered Autogyro with Articulated Rotors and Attitude Control using Differential Rotor Braking

Tasnia Noboni and Tuhin Das

A tethered autogyro with articulated rotors can operate as an unmanned aerial vehicle capable of energy-efficient, long-duration deployment by utilizing ambient wind energy to sustain flight. This article presents a model-based attitude control technique for such a system using a full-fidelity dynamic model. Using Lagrangian approach combined with Blade Element Momentum Theory and catenary mechanics, a previously developed 2D hybrid model is extended to three dimensions. The new model describes the complete rigid-body motion of the frame, including roll and yaw dynamics, and is augmented with rotor speed and flapping degrees of freedom for each blade. Equilibrium characteristics are examined through steady-state responses and compared with the prior model. The resulting trends of equilibria are found to be consistent with those reported in the literature. A feedback control strategy based on regenerative differential rotor braking is developed to modulate all three attitude angles. Simulations demonstrate effective attitude regulation and stable flight.
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Instrumentation and Detectors · Cross-listed from cond-mat.mtrl-sci

Multitask Scanning Probe Microscopy

Aditya Raghavan, Yu Liu, Ian Mercer et al. (+2 more)

Scanning probe microscopy provides nanoscale access to structural, electrical, electromechanical, magnetic, and mechanical properties of materials. Its increasing use for wafer-scale characterization and combinatorial materials exploration creates a need to distribute measurements efficiently across large spatial domains. This is particularly important when available modalities differ in acquisition time and potential for tip and sample damage, making exhaustive multimodal mapping over spatial grids impractical. Here, we demonstrate multitask scanning probe microscopy, a live, closed-loop workflow in which a multitask Gaussian process learns spatial and cross-modal relationships and autonomously selects both the next measurement location and the next experimental protocol. The approach is implemented on an automated large-sample atomic force microscope and demonstrated on a composition-spread AlScN wafer using tapping-mode and Dual AC Resonance Tracking (DART) measurements. Paired initial measurements establish the relation between the tasks, after which noncoincident measurements are used to update both response landscapes. The resulting workflow extends active learning in scanning probe microscopy from spatial sampling to autonomous allocation of measurement modalities and provides a basis for combining rapid, weakly perturbative imaging with slower contact, electrical, electromechanical, magnetic, or spectroscopic measurements.
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All authors Aditya Raghavan, Yu Liu, Ian Mercer, JP Maria, Sergei Kalinin

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

Electronic conductivity in anharmonic crystals: Phonon dephasing in the electron-phonon interaction

Mingran Kong and Bartomeu Monserrat

The electron-phonon interaction underpins many material properties, for example, the conductivity of metals and the optoelectronic response of semiconductors. First-principles calculations of the electron-phonon interaction are a powerful tool to quantitatively describe many of these properties in increasingly complex materials. However, one key assumption of all calculations is that phonons have infinite lifetimes, an approximation that may break down when anharmonic phonon-phonon interactions are strong. In this work, we present a theory for the interaction of electrons with finite-lifetime phonons experiencing dephasing. Using a first-principles implementation of the theory, we find that anharmonic dephasing dramatically enhances electron-phonon scattering rates in metallic MgB2. Microscopically, phonon-phonon interactions create new scattering channels that increase the phase space available for electron-phonon scattering. As a result, anharmonic dephasing strongly suppresses conductivity in MgB2, bringing the calculated values substantially closer to experiment within the Boltzmann transport equation framework. This example establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon scattering, and the microscopic mechanism suggests that anharmonic dephasing could play an important role in the conductivity of many metals. More broadly, our theory and first-principles implementation of anharmonic dephasing in the electron-phonon interaction provides a solid foundation to explore this regime in other materials.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci

Anharmonic dephasing in the electron-phonon interaction

Mingran Kong and Bartomeu Monserrat

Electron-phonon coupling has been a central topic in condensed matter physics for decades, and firstprinciples methods have demonstrated remarkable success in quantitatively capturing its role in a wide variety of physical phenomena and materials. Conventional calculations of electron-phonon coupling typically assume that phonons have infinite lifetimes, but phonons can exhibit finite lifetimes due to anharmonic phonon-phonon interactions. In this work, we derive an expression for the electron-phonon coupling scattering rates including the effects of anharmonic three-phonon interactions, which lead to phonon dephasing and finite phonon lifetimes. We also describe a first-principles implementation of this anharmonic electron-phonon coupling which can be seamlessly integrated within existing workflows for the evaluation of electron-phonon and phonon-phonon coupling interactions. Finally, we present calculations of electron-phonon scattering rates including phonon dephasing in a range of materials, and discuss the different microscopic mechanisms by which anharmonic phonons influence electron-phonon coupling. This study establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon coupling, and provides a platform to explore these effects in a wide range of materials and phenomena.
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Optics

Population-inversion map of the mesospheric sodium ladder: continuous-wave and pulsed pumping schemes for directed emission

Yucheng Yang, Chunyang Lei, Kai Guo et al. (+2 more)

Directed mirrorless lasing from the mesospheric sodium layer has been proposed as a way to overcome the isotropy of laser guide star fluorescence, with demonstrated cell-scale analogues and a demonstrated stand-off magnetometry application. Several transition paths on the Na ladder compete for the same pump photons. We build a ten-level rate-equation model of the ladder from NIST transition probabilities and evaluate every electric-dipole line under four continuous-wave pumping schemes, both in a Doppler-averaged treatment and in a velocity-selective treatment appropriate for the collision-poor mesosphere. Three design-relevant results emerge. At practically accessible continuous-wave irradiances the column-gain exponents remain far below unity, consistent with published feasibility estimates; the value of the classification is to identify which lines, schemes, and pulse formats merit further study.
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All authors Yucheng Yang, Chunyang Lei, Kai Guo, Chi Peng, Zongpeng Pan

Computational Physics · Cross-listed from cond-mat.supr-con

Prediction of BaBiO$_3$-like superconducting perovskites in K-doped SrAsO$_3$

Zhihong Yuan, Rui Liu, Pengyu Zheng et al. (+1 more)

Using first-principles calculations, we predict a new perovskite compound SrAsO$_3$ . The undoped cubic phase has pronounced soft-phonon instabilities, which are gradually suppressed upon K doping the Sr site. The cubic phase becomes dynamically stable for K-doping levels above approximately 60%, and the stabilized K-doped phases are metallic with predicted conventional phonon mediated superconductivity. Moreover, the inclusion of nonlocal exchange interactions broadens the electronic bandwidth, enhances the electron-phonon coupling (EPC) strength, and increases the superconducting transition temperature ($T_c$) of these doped compounds. In particular, the HSE06 hybrid exchange-correlation functional corrected EPC constant $\lambda$ reaches 1.41 for Sr$_{0.4}$K$_{0.6}$AsO$_3$, corresponding to a predicted $T_c$ of 44.3 K. These results suggest that SrAsO$_3$ is a BaBiO$_3$-like superconducting perovskite driven by strong electron-phonon coupling.
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All authors Zhihong Yuan, Rui Liu, Pengyu Zheng, Zhiping Yin

Optics

Dispersion-managed octave soliton microcombs in heterostructured microresonators

Xinghong Li, Wenxin Zhang, Yiyang Lu et al. (+5 more)

Controlling group velocity dispersion is of fundamental importance in ultrafast optics, particularly for supercontinuum generation and optical frequency comb synthesis. However, the simultaneous, independent tailoring of multiple dispersion coefficients over an ultra-broad bandwidth remains a formidable challenge in conventional nanophotonic platforms. Here, we demonstrate a robust strategy for broadband dispersion management using heterostructured microresonators comprised of adiabatically concatenated waveguides with distinct geometries. By meticulously engineering the local dispersion profiles, we can flexibly synthesize the global effective dispersion coefficients of different orders, effectively expanding design degrees of freedom beyond conventional limits. As a benchmarking demonstration, we fabricate heterostructured silicon nitride microresonators using a commercial foundry process and successfully generate octave-spanning soliton microcombs with a repetition rate as low as 118 GHz. These microcombs feature deterministically tunable dispersive waves operating across the 290-310 THz range. Such octave-spanning microcombs with detectable repetition rates and carrier-envelope offset frequencies are readily applicable to f-2f self-referencing in optical clocks and frequency synthesizers. The proposed heterostructured architecture establishes a versatile paradigm for generating ultrawideband soliton microcombs with tailorable spectral profiles.
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All authors Xinghong Li, Wenxin Zhang, Yiyang Lu, Zhaoyi Wang, Qingzhuo Xuan, Shangyuan Li, Xiaoping Zheng, Xiaoxiao Xue

Optics

Wafer-scale monolithic integration of Ce:YIG films and magneto-optical isolators on silicon

Tianchi Zhang, Yucong Yang, Weihao Yang et al. (+9 more)

Silicon integrated cerium doped yttrium iron garnet (Ce:YIG) thin films are promising candidates for integrated nonreciprocal photonic devices, cryogenic photonic modulators and optical computing applications. However, previously reported Ce:YIG thin film on silicon is limited to milimeter sizes. Wafer-scale integration and non-destructive characterization of high quality Ce:YIG thin films on silicon has been elusive. Here, we report growth of 4-inch wafer-scale Ce:YIG thin films on silicon substrates by radio-frequency magnetron sputtering. Strong Faraday effect of 2318 deg/cm, low propagation loss of 80 dB/cm and excellent thickness uniformity of 3.5% is demonstrated across the 4-inch silicon wafer. Furthermore, a custom designed wafer-scale, non-destructive magneto-ellipsometry was established to characterize the film thickness, optical constants and magneto-optical constants across the wafer. Wafer-scale integration of ring resonator type magneto-optical isolators are also demonstrated. Our work demonstrates a step forward toward wafer-scale heterogeneous integration and characterization of magneto-optical thin films on silicon, providing material candidates for non-reciprocal photonic device arrays, magneto-optical in-memory computing networks and integrated magneto-optic magnetometers.
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All authors Tianchi Zhang, Yucong Yang, Weihao Yang, JieJun Su, Tianyi Ma, Xuan Zhao, Junxian Wang, Di Wu, Zhenyuan Ren, Yi Shuai, Zixuan Wei, Lei Bi

Applied Physics

Optimization of the Repumping Parameters for a Sodium Laser Guide Star Magnetometer

Yucheng Yang, Chunyang Lei, Kai Guo et al. (+1 more)

A sodium laser guide star operated as a mesospheric magnetometer modulates a 589 nm laser at the local Larmor frequency and usually diverts a fraction of its power to a repumping light that recovers atoms lost to the dark ground state.The polarization, read out for the most strongly driven velocity group, calls for 2.8 times the flux optimal fraction, and a shot noise figure of merit combining the two observables for 2 times, beyond the range commercial guide star lasers provide.
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All authors Yucheng Yang, Chunyang Lei, Kai Guo, Shuai Wang

Sunday 9 August

General Physics

Algebraic decomposition and topological fibrations of the $U(4) \to SU(2)$ quotient space

Dimitris Mastoridis and Konstantinos Kalogirou

We investigate the algebraic and topological properties of the unitary group $U(4)$ subjected to a non-standard continuous symmetry breaking cascade down to an $SU(2)_H$ subgroup. By explicitly embedding the unbroken $SU(2)_H$ symmetry into the lower-right quadrant of the fundamental matrix representation, we demonstrate that the resulting 12-dimensional quotient space, $SU(4)/SU(2)_H$, undergoes a strictly asymmetric geometric partition. This specific breaking pattern uniquely isolates an 8-dimensional sector that retains closed commutation relations, forming a rigorous $\mathfrak{su}(3)$ Lie subalgebra. Concurrently, it isolates a 4-dimensional off-diagonal sector that fails to close algebraically, generating a purely non-linear topological coset. By analyzing the global spherical fibrations of the manifold, we show that this non-linear territory reduces to a $\mathbb{C}P^1 \cong S^2$ base space. Consequently, continuous mappings from a 3-dimensional spatial boundary are classified by the third homotopy group, $\pi_3(S^2) \cong \mathbb{Z}$, guaranteeing absolute vacuum stability via the integer-quantized Hopf invariant. Ultimately, this framework demonstrates that a non-simple unitary group can organically provide a mathematically rigorous geometric template capable of simultaneously accommodating both continuous gauge symmetries and stable, non-perturbative topological sectors.
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Physics and Society

The Calibration-Leverage Tradeoff in Exactly Solvable Win-Probability Models

Devansh Mishra

We study ball-by-ball win probability (WP) for second-innings run chases in Twenty20 cricket, built as an exactly solvable Markov model: we estimate a single object, the per-ball outcome distribution over {0,...,6, wicket}, and derive WP for every game state by backward induction over the acyclic (balls, wickets, runs-required) chase graph. This construction makes WP an exact martingale, which in turn makes leverage (how much a ball can swing WP) and win probability added (WPA) well-defined and exactly attributable; we use them to confirm that finishers and death bowlers occupy the highest-leverage moments. We then show the model's WP is systematically miscalibrated, and that this is not incidental. Localizing the error, we rule out tail-thinning and marginal mis-estimation (the model's per-ball outcome distribution matches the empirical one to a total variation of at most 0.02 at every required run rate). The only remaining cause is unmodelled dependence given the state, and we identify it: a permutation-null decomposition shows short-range sequential run-scoring persistence (roughly 3-5 balls; innings-level heterogeneity contributes only about 18%; wickets, if anything, anti-cluster). A block-bootstrap simulator that injects the real dependence while holding the marginals fixed closes 26% of the calibration gap (replicated over six seeds), saturating at block lengths of about 20 balls, consistent with the measured correlation range; this is a constructive lower bound that confirms the diagnosis. The result is a structural tradeoff relative to the (balls, wickets, runs) state description: exact leverage requires the martingale, the martingale requires conditional ball independence on that state, and that independence is what miscalibrates the WP. Exactly attributable leverage and well-calibrated WP cannot be obtained from the same object over this state.
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Data Analysis and Statistics

Analytically Consistent Reconstruction of Finite Data Using Padé Sequences

Emerson Díaz, Balma Duch and Pere Masjuan

Reconstructing the analytic structure of a function from finite datasets is a fundamental problem across theoretical, numerical, and experimental physics. While Padé approximants provide a natural framework, finite-information effects, as well as statistical and systematic uncertainties, may obscure the underlying analytic structure and limit reconstruction reliability. In this work, we reinterpret the appearance of Froissart doublets not merely as numerical artifacts but as diagnostic objects carrying information about the analytic consistency of the input data. Accordingly, we develop a general Padé-based algorithm that exploits the dynamics of Froissart doublets along Padé sequences to identify localized inconsistencies and iteratively reconstruct the analytic structure most compatible with the data. The method requires no model for the origin of the inconsistencies and distinguishes genuine analytic features from spurious structures induced by finite-information effects. We validate it using Stieltjes functions, realistic pseudo-experimental datasets with statistical and systematic uncertainties, and general holomorphic functions. The complete algorithm is provided as a supplementary Mathematica notebook in an open GitLab repository.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci

Temperature-Driven Sequential Modeling for the Prediction of Annual Power Conversion Efficiency Profiles of Organic Photovoltaic Materials: Douala Case Study

Steve Cabrel Teguia Kouam, Rockefeller Rockefeller, Raoult Dabou Teukam et al. (+4 more)

Organic photovoltaic (OPV) materials are promising candidates for distributed solar energy in tropical regions, yet existing virtual screening tools report static power conversion efficiency (PCE) values at standard testing conditions (STC) that fail to capture the temperature-driven performance degradation experienced under real deployment conditions. Here we introduce a Climate-Native computational framework that forecasts the annual PCE profile of OPV donor molecules under geographically realistic operating conditions. The framework combines GFN2-xTB molecular dynamics with an equivariant graph neural network surrogate ($268$ Neyman-stratified CEP molecules; $120,600$ training geometries; $\sim 1050\times$ speedup over explicit quantum chemistry) and sequential deep learning models trained on annual time series anchored in NASA POWER climate data for Douala, Cameroon, and validated by zero-shot transfer to Yaoundé and Maroua. Applied to $\sim 30,000$ molecules from the Harvard Clean Energy Project (CEP) and validated against $350$ HOPV15 experimental device measurements, the framework demonstrates that sequential models trained on full molecular dynamics trajectories outperform time-averaged baselines ($35\%$-$48\%$ relative MAE improvement over static baselines), confirming that thermal conformational dynamics carry information beyond mean geometry. We further introduce a seasonal stability score that reranks OPV candidates by performance consistency under tropical conditions, identifying molecules whose deployment suitability differs substantially from their static PCE ranking.
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All authors Steve Cabrel Teguia Kouam, Rockefeller Rockefeller, Raoult Dabou Teukam, Jean-Pierre Tchapet Njafa, Patrick Sorrel Mvoto Kongo, Jean-Pierre Nguenang, Serge Guy Nana Engo

Popular Physics

Certified Misty-State Rewriting (A Question-and-Answer Guide)

Tony Newton and Dan-Adrian German

Quantum mechanics is difficult to teach because its conceptual content and mathematical notation usually arrive together. Rudolph's misty-state language was designed to decouple those burdens; basis states are visual objects, clouds represent superposition, gates act by elementary replacement rules, and destructive interference appears as cancellation rather than as matrix calculation. An elementary “misty-state” language can make quantum circuits accessible to students before they master complex linear algebra. Development presented here was initiated/led by the first author. The contribution is not a replacement for complete graphical calculi such as ZX or sum-over-paths. It is a source-specific bridge from an intuitive educational notation to a mathematically explicit, executable, and falsifiable semantics.
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Atmospheric and Oceanic Physics

Deep Learning-Based Statistical Downscaling of Sea Surface Temperature Using a Residual Corrective Neural Network

Onkar Jadhav, Tim French, Ivica Janekovic et al. (+2 more)

The large-scale oceanic and atmospheric forecasts provided by global climate models typically lack sufficient resolution to accurately capture the response of the coastal ocean to atmospheric forcing and coastal circulation that drive fine-scale SST variability. Dynamical downscaling is computationally prohibitive, when applied to extensive coastlines, predictive ensembles, or long time periods. Therefore, this work presents a statistical downscaling of sea surface temperature (SST) from the seasonal coupled ocean-atmosphere forecast system (ACCESS-S2) using machine learning techniques. This study proposes a novel deep learning framework that uses a U-Net to generate an initial high-resolution SST estimate, which is subsequently refined using a residual corrective approach. The target SST fields are derived from the Regional Ocean Modeling System (ROMS). This two step approach called Residual Corrective Neural Network (RCNN) progressively refines initial U-Net predictions by incorporating dynamically scaled residuals at each step, enabling accurate capture of broad patterns and fine-grained features such as eddies and fronts. We also introduce a custom loss-assisted RCNN variant to improve performance during extreme events, which may be absent from training data due to climate-driven shifts in SST extremes. The framework efficiently downscales SST along the west coast of Australia. A 2011 marine heatwave case study shows that the RCNN improves ACCESS-S2 SST predictions by increasing horizontal resolution from 25 km to 2 km, enabling identification of fine-scale anomalies unresolved in the ACCESS-S2 dataset. This balance between computational efficiency and accuracy supports applications in coastal impact assessment and marine ecosystem studies.
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All authors Onkar Jadhav, Tim French, Ivica Janekovic, Nicole L. Jones, Matthew Rayson

Atmospheric and Oceanic Physics

Do AI Forecast Ensembles Sample the Correct Conditional Distribution?

Lucas J. Howard and Elizabeth A. Barnes

Ensemble forecasting aims to sample the conditional distribution of outcomes; whether AI forecast ensembles do this correctly in a joint sense remains largely untested. We train a diffusion model for probabilistic subseasonal coastal sea level forecasts at eight US East Coast tide gauge stations, with sea level derived from reanalysis, and find that marginal and joint forecast quality decouple: positive skill at every station and lead time marginally, while joint spatial structure is worse than climatological draws. A shuffle-based permutation decomposition reveals this failure is invisible to the energy score but detected by the variogram score. Lorenz-96 experiments across 0.7-170 equivalent years show the gap persists regardless of training volume and is reproduced by a linear baseline, indicating structural inadequacy of the learned distribution. A dynamical ensemble does not replicate the failure while a deterministic emulator does, suggesting it is specific to learned emulators rather than ensemble forecasting generally.
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Chemical Physics

Real-Time Approach to the Dynamical Bethe-Salpeter Equation for Finite Systems

Tucker Allen, Barry Y. Li and Daniel Neuhauser

We present a real-time linear-response approach to solving the dynamical Bethe-Salpeter equation (BSE). The polarization part of the screened interaction is obtained from time-dependent Hartree propagation of the one-particle density matrix within an orbital basis-set representation. The frequency convolution defining the dynamical kernel is evaluated as a product in time, avoiding numerical integration and storage of the full screened Coulomb operator. The resulting nonlinear eigenvalue problem is then solved directly, going beyond the static screening approximation with full-frequency dependence in the screened interaction. We validate the method by calculating the low-lying singlet and triplet excitation energies of water, formaldehyde, and acetylene. While the deterministic scaling remains $\mathcal{O}(N^6)$, the time propagation formulation is readily compatible with grid-based stochastic sampling methods, which will open the possibility for dynamical BSE calculations of very large systems.
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Optics

Multimode Quantum Effects of Optical-Axis Misalignment in Gravitational-Wave Interferometers

Aleksandr V. Karpenko and Sergey P. Vyatchanin

We develop a multimode quantum model of optical-axis misalignment in a simplified representation of the differential mode of an Advanced LIGO interferometer. The system is described as two coupled optical resonators corresponding to the signal extraction cavity and the arm cavity. Analytical expressions for the mode-mixing coefficients are derived, establishing a direct connection between geometrical perturbations of optical elements and multimode optical dynamics. Using the developed formalism, we investigate the influence of optical-axis misalignment on quantum-noise-limited sensitivity and injected squeezed states. We show that misalignment between the signal extraction cavity and the arm cavity leads to significant sensitivity degradation, frequency-dependent rotation of the squeezing ellipse, and a reduction of the observable squeezing in the fundamental spatial mode. At the same time, the injected squeezing is not destroyed but redistributed among coupled spatial modes. The resulting mode coupling generates quantum correlations between the fundamental and higher-order modes and leads to spatial-mode entanglement verified using the positive partial transpose criterion. Our results demonstrate that optical-axis misalignment should be treated as a coherent multimode quantum process rather than as a simple optical loss mechanism.
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Applied Physics

Giant Rotational Meta-Doppler from Genetically Designed Superscatterers

Dmytro Vovchuk, Sergey Geyman, Konstantin Grotov et al. (+10 more)

The motion of a rigid body interacting with a wave leaves spectral signatures, with the Doppler shift as the dominant contribution. Since any motion can be decomposed into translational and rotational components, rotational Doppler provides additional information about the object's dynamics. In the electromagnetic domain, rotating objects generally produce rotational Doppler, or micro-Doppler, signals determined by the symmetry and spatial structure of the scattering process. For objects that are subwavelength or comparable in size to the wavelength, the response is typically dominated by the lowest dipolar scattering channel, so the leading spectral component commonly appears at twice the angular frequency. Here, we introduce the concept of artificially engineered rotational micro-Doppler by designing a compact, strongly scattering structure that operates through a high-order multipolar cascade of resonances, thereby producing a giant enhancement. Magneto-electric arrays composed of strongly coupled electric and magnetic resonators are optimized in the GHz range using a covariance matrix adaptation genetic algorithm to maximize the micro-Doppler frequency. Unlike conventional higher-order multipole designs used in superscatterers for a specific angle of incidence and polarization, our approach jointly optimizes excitation and scattering under radar-relevant conditions for a rotating blade. The resulting arrays exhibit a giant rotational meta-micro-Doppler response, exceeding the dipolar limit by two orders of magnitude and mapping rotations of tens of hertz into the kilohertz range. Beyond its fundamental significance, this mapping has practical value because it shifts rotor micro-Doppler signatures well above slow-moving radar clutter, thereby improving the detectability of slow motion.
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All authors Dmytro Vovchuk, Sergey Geyman, Konstantin Grotov, Dmitry Dobrykh, Andrey Machnev, Anna Mikhailovskaya, Susanna Rozental, Anton Kharchevskii, Mikhail Tsukerman, Vjaceslavs Bobrovs, Aviel Glam, Alexander Gumennik, Pavel Ginzburg

Medical Physics

Toward CT-Equivalent Image Quality in Low-Dose Radiotherapy Planning: Conditional Diffusion-Based CBCT-to-CT Synthesis and the Impact of CBCT Input Representation

Alzahra Altalib, Chunhui Li, Christopher Hamill Taylor et al. (+2 more)

During standard radiotherapy planning, repeated CT acquisitions are often required for patient registration, verification, and adaptive planning, resulting in increased cumulative X-ray dose. To mitigate this, low-dose cone-beam CT (CBCT) is routinely acquired during treatment delivery. However, CBCT image quality remains insufficient for accurate dose calculation and adaptive radiotherapy planning due to increased scatter, noise, beam hardening, and reconstruction related artifacts. This study develops a supervised deep learning based CBCT to CT synthesis framework using a conditional denoising diffusion probabilistic model (DDPM), where the generation of a CT-based planning for accurate positioning and dose calculation is obtained using generative models with low dose CBCT imaging. Beyond demonstrating CBCT to CT synthesis, the primary objective is to investigate how the representation of CBCT input data, either standard clinical DICOM CBCT images or filtered back-projection (FDK) reconstructions from raw projection data, affects the performance of diffusion based CT synthesis. The overarching aim is to assess whether physics aware CBCT representations better support CT-equivalent image quality while maintaining reduced imaging dose in radiotherapy workflows.
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All authors Alzahra Altalib, Chunhui Li, Christopher Hamill Taylor, Sankar Pillai, Alessandro Perelli

Atomic Physics

Rotational laser spectroscopy of the $X^1\Sigma_g^+\rightarrow B^1\Pi_u$ transition of $\text{Rb}_2$ molecule in a supersonic beam: As good as it gets

David Rodríguez Fernández, Manuel Alejandro Lefrán Torres, Jaime Javier Borges Márquez et al. (+6 more)

High-resolution laser spectroscopy of the $^{85}\mathrm{Rb}_2$, $^{85}\mathrm{Rb}^{87}\mathrm{Rb}$, and $^{87}\mathrm{Rb}_2$ isotopologues has been performed in a supersonic molecular beam using a continuous-wave (cw) tunable diode laser. A total of 958 rovibronic transitions were recorded up to $7~\mathrm{cm}^{-1}$ below the vibrational band heads of the $X^1\Sigma_g^+(v''=0)\rightarrow B^1\Pi_u(v'=1,2)$ and $X^1\Sigma_g^+(v''=1)\rightarrow B^1\Pi_u(v'=1)$ bands, with a spectral resolution of $3.3\times10^{-4}$~cm$^{-1}$. Although restricted to the $v'=1$ and $v'=2$ vibrational levels of the excited $B^1\Pi_u$ state, the measurements extend previous work by Amiot and Vergès [Chemical Physics Letters 274, 91 (1997)] through substantially higher resolution and dense low-$J'$ rotational data for all three isotopologues. A global least-squares analysis combining the new and published data, yields improved Dunham coefficients for the excited $B^1\Pi_u$ state, significantly refines rotational and rovibrational coupling constants. In addition, the $\Lambda$-doubling constants of $B^1\Pi_u$ state were determined for the three isotopologues.
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All authors David Rodríguez Fernández, Manuel Alejandro Lefrán Torres, Jaime Javier Borges Márquez, Marcos Roberto Cardoso, Amrendra Pandey, Romain Vexiau, Olivier Dulieu, Nadia Bouloufa-Maafa, Luis Gustavo Marcassa

Plasma Physics

Energy-optimized scaling laws for self-guided laser wakefield accelerators

Petr Valenta, Marcel Lamač, Kyle G. Miller et al. (+4 more)

Laser wakefield acceleration promises compact electron accelerators for applications in medicine, industry, and fundamental science. Yet, despite rapid progress, accurately predicting the electron energy attainable in a given experimental configuration and the acceleration length required to reach it remains an open challenge. Here we use Bayesian optimization combined with advanced particle-in-cell simulation techniques to determine the maximum electron energy that a self-guided laser wakefield accelerator driven by a laser of a given energy and wavelength can produce. By systematically optimizing the accelerator performance across a range of laser energies and wavelengths, we derive energy-optimized scaling laws. These scaling laws yield the highest electron energy over the shortest acceleration length possible, are expressed solely in terms of laser energy and wavelength, and are accompanied by the complete set of laser and plasma parameters required to enable the scaling. The resulting scaling laws provide practical guidance for designing state-of-the-art laser wakefield acceleration experiments operating at their fundamental performance limits.
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All authors Petr Valenta, Marcel Lamač, Kyle G. Miller, Brandon K. Russell, Gabriele M. Grittani, Alec G. R. Thomas, Sergei V. Bulanov

Optics

Nonresonant optomechanical control of structural phases

Jiaojian Shi, Yijing Huang, Christian Heide et al. (+24 more)

Optical tweezers demonstrate how light can exert forces to trap, repel, and manipulate microscopic particles without absorption. Recent theory has suggested that such forces can extend beyond particle manipulation to drive structural phase transitions in solids. Here we apply this optomechanical principle to tin selenide (SnSe), a material where proximity to several different structural phases gives rise to its high thermoelectric figure of merit and makes it a candidate for a switchable topological crystalline insulator. Whereas the force for standard optical tweezers arises from a gradient in the intensity of a light field, the optomechanical force is mediated by a gradient in the dielectric constant as a function of phonon coordinate. Unlike conventional methods that rely on resonant excitation and absorption through the imaginary part of the dielectric function, this approach operates dispersively through the real part and can be directly driven by Raman processes, enabling selective transitions with reduced energy cost and ultrafast response. Using time-domain Raman scattering, we show that above a critical mid-infrared field strength the $A_g$ Raman modes disappear abruptly without softening, signaling the formation of a new structural phase. This phase, distinct from those induced by heating or carrier excitation, exhibits large-amplitude and long-lived modulations in its optical response. Complementing this observation, we show also evidence for an equivalent DC-field-driven structural phase transformation to a higher symmetry phase, as observed by atom probe tomography. Our study demonstrates the concept of nonresonant optomechanical phase control and defines novel opportunities for synthesizing hidden structural phases with unique functional properties.
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All authors Jiaojian Shi, Yijing Huang, Christian Heide, Elias Hilderbrand, Carl Friedrich Schon, Jan Kottgen, Matthias Wuttig, Burak Guzelturk, Isabel Sedwick, Yukun Li, Haowei Xu, Yuejun Shen, Pooja Donthi Reddy, Viktoryia Shautsova, Mohammad Taghinejad, Duan Luo, Mark L. Brongersma, Kunal Mukherjee, Yuki Kobayashi, Andrew F. May, Eamonn Hughes, Mariano Trigo, David A. Reis, Ju Li, Jian Zhou, Shambhu Ghimire, Aaron M. Lindenberg