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Medical Physics · Cross-listed from eess.IV

DoReMe: Dual optimization of Reconstruction and Motion estimation for self-navigated free-breathing abdominal MRI using Gaussian Splatting

Majd Helo, Dominik Nickel and Thomas Kuestner

Purpose: Free-breathing abdominal MRI is limited by respiratory motion, which introduces image artifacts and k-space inconsistencies. Existing reconstruction approaches often depend on pre-estimated motion fields or external respiratory surrogate signals. We propose a coupled reconstruction-motion estimation algorithm for self-navigated free-breathing acquisition, in which motion is represented by compact Gaussian primitives and jointly refined with the image estimates during iterative reconstruction. Methods: An iterative reconstruction that alternates between data consistency updates and motion modelling was proposed. Respiratory motion was represented using Gaussian primitives. A Gaussian splatting was integrated into the reconstruction algorithm. The method was evaluated on self-navigated free-breathing Cartesian gradient-echo (GRE) acquisition in four healthy volunteers, including retrospective scan shortening experiments, and was compared with regularized compressed sensing (CS) reconstruction. Results: Respiratory motion states were reconstructed in approximately 1.5 min. Compared with CS, the proposed method improved visual image quality, particularly in coronal liver views, and better preserved anatomical structures in retrospectively shortened acquisitions. These findings provide proof of concept for the proposed method. Conclusion: The proposed coupled reconstruction-motion estimation algorithm improved visual image quality compared with CS alone. Gaussian primitives provided a compact and sufficiently flexible representation of nonrigid respiratory motion with practical runtime, supporting further scanner integration and validation in larger cohorts.
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Materials Science

Engineering Correlated Transparent Conductors via Metal-Insulator Transition Proximity

Amit Cohen, Nofar Tuval, Maria Baskin et al. (+5 more)

Transparent conductors are key functional materials in modern optoelectronic devices. Their performance is governed by an inherent trade-off between optical transparency and electrical conductivity. Correlated metallic oxides offer an attractive workaround to this compromise, where narrow partially-filled bands provide high conductivity, while the absence of visible-range transitions enables optical transparency. Despite this promise, transparency and conductivity remain coupled through carrier density and electronic coherence. Here, we use proximity to a metal-insulator transition (MIT) as a design principle for engineering this balance in correlated-oxide transparent conductors. Epitaxial Ti-substituted $SrVO_3$ films serve as a model platform where the optical window and metallicity are tuned simultaneously. We demonstrate and explain a systematic broadening of the optical window to regimes relevant for silicon photovoltaics. This gain is counterbalanced by carrier depletion and disorder, which drive the loss of coherent transport near the composition-driven MIT. A Haacke figure-of-merit analysis identifies the optimal composition range near the MIT, where the loss of metallic transport is accompanied by persistent near-Fermi-level spectral weight, indicating disorder-assisted localization together with correlation-driven spectral-weight redistribution. These findings establish proximity to an MIT as a general materials-design strategy, using electronic filling as a tuning knob for the transparency-conductivity balance in correlated-oxide transparent conductors.
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All authors Amit Cohen, Nofar Tuval, Maria Baskin, Tien-Lin Lee, Tom Tiwald, Scott A. Chambers, Sophie D. Beck, Lior Kornblum

High Energy Physics (Phenomenology)

Pythia-Contrib: a modular contribution framework for the Pythia 8 event generator

Benoit Assi, Christian Bierlich, Rikab Gambhir et al. (+6 more)

Pythia is a general-purpose Monte Carlo event generator used in particle, astroparticle, and nuclear physics, by theorists and experimentalists, to simulate particle collisions. Because of the size and diversity of the user community, it is challenging to address all of the needs for new and varied physics models. This paper describes the Pythia-Contrib system, which allows for third-party developers to contribute code to Pythia without introducing external software dependencies to the Pythia code base.
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All authors Benoit Assi, Christian Bierlich, Rikab Gambhir, Philip Ilten, Tony Menzo, Stephen Mrenna, Manuel Szewc, Michael K. Wilkinson, Jure Zupan

Quantum Physics

Post-Optimization Subspace Corrections to Quantum Ansätze

Prince Frederick Kwao, Bharath Sambasivam, Jason Saroni et al. (+3 more)

Circuit depth and measurement count are the main limitations for chemical applications of the leading variational quantum algorithms on quantum computers. We show that both resource requirements can be reduced by augmenting adaptive variational quantum algorithms with post-optimization corrective techniques. We focus on two such techniques—Hamiltonian-moment Krylov subspace diagonalization and the identity-augmented quantum self-consistent equation of motion (q-sc-EOM)—applied to optimized ADAPT-VQE states without further ansatz growth or nonlinear optimization. Across molecular systems studied with up to 20 qubits, first-order Krylov correction reduces the optimized iterations (and the corresponding number of adaptive layers) needed to reach the $1.6~\mathrm{m}E_h$ threshold by up to approximately sixfold, with a general trend toward larger reductions at higher determinant Rényi entropy. We also find measurement-cost reductions of up to approximately fortyfold using a suitable resource-cost model. Identity-augmented q-sc-EOM improves molecular potential-energy curves obtained from truncated ADAPT-VQE ansätze with limited expressivity and recovers accuracy from states produced by sampled operator ranking without additional gradient-based operator selection, providing an advantage when small pool gradients make selection measurement intensive. Together, these post-optimization corrections offer routes to improve energy accuracy and reduce adaptive circuit growth in quantum algorithms as quantum hardware advances.
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All authors Prince Frederick Kwao, Bharath Sambasivam, Jason Saroni, Srivathsan Poyyapakkam Sundar, Edwin Barnes, Ayush Asthana

Medical Physics

Can $^{225}$Ac be imaged on a long axial field-of-view PET/CT with standard clinical settings?

Lorenzo Mercolli

Purpose: The $^{225}$Ac decay chain includes $^{209}$Tl, whose prominent 1567 keV gamma line can create electron-positron pairs. We investigated whether a long axial field-of-view (LAFOV) PET/CT can image $^{225}$Ac using standard clinical acquisition and reconstruction methods. Methods: A syringe placed next to a vial (5.89 and 10.29 MBq of $^{225}$Ac activity) and a NEMA IEC body phantom (sphere activity concentration 4.56 kBq mL$^{-1}$) were scanned for 45 and 60 min, respectively, on a Biograph Vision Quadra (Siemens Healthineers). To support our findings, FLUKA simulations scored the annihilation locations around a $^{225}$Ac point source. Results: The contours of the syringe and vial were visible despite high noise, but the NEMA spheres could not be distinguished from the background. As illustrated by the FLUKA simulations, the number of annihilation events decreases exponentially according to the mean free path of the 1567 keV photon in the surrounding medium. Conclusion: A LAFOV PET/CT can detect positrons created by pair production of the main $^{209}$Tl gamma line. However, these positrons are created where the photons interact with the surrounding medium rather than at the location of the $^{209}$Tl decays, which rules out standard PET imaging of $^{225}$Ac.
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General Relativity and Quantum Cosmology

Gravity from generalized entropy

Hussain Gohar

Gravity from entropy (GfE) identifies its Lagrangian with the geometric quantum relative entropy (GQRE) between the spacetime metric and a metric induced by matter and curvature, treating the metric itself as a quantum operator. We extend this construction to the Tsallis, Rényi, and Sharma-Mittal families, which we call gravity from generalized entropy (GfGE), and determine their common Einstein limit, weak-field spectra, auxiliary-field formulation, and horizon entropy. The entropy choice controls the leading higher-curvature terms and additional modes. We confirm that the linearized GfE spectrum contains a healthy scalar and a Planck-scale tachyonic spin-2 ghost. We identify the conditions that remove this ghost: curvature must enter through its scalar trace, or the entropy generator must be flat to quadratic order at the identity. The latter gives exact general relativity for Tsallis at $q=0$ and ghost-free $f(R,L_m)$ theories for Rényi and Sharma-Mittal. On shell, the auxiliary G-field is proportional to the tensor in Wald's entropy formula. For analytic entropy functions, horizons with a single curvature scale have an area term followed by constant and inverse-area corrections. We also extend the volume-constraint cosmological constant to the full family; its leading entropy dependence is set by the scalar mass. A finite set of entropy-function derivatives controls the leading weak-curvature departures from general relativity.
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Solar and Stellar Astrophysics

A Distinct Type of Standstill in Ultra-Compact White Dwarf Binaries

Jan Kára, Liliana Rivera Sandoval, Iwona Kotko et al. (+3 more)

AM CVn stars are ultra-compact, semi-detached binaries consisting of a white dwarf primary and a hydrogen-poor secondary. In this work, we analyse the AM CVn-type systems MGAB-V270, ZTF18aaxuusk and ASASSN-19ct, which have similar properties and show unusual post-superoutburst behaviour. We focus on the occurrence of standstill-like phases. In MGAB-V270, superoutbursts are followed by a series of echo outbursts that evolves into a standstill-like phase before the system returns to quiescence. ZTF18aaxuus shows similar post-superoutburst activity, with one echo-outburst series also developing into a standstill-like phase. ASASSN-19ct exhibits comparable echo outbursts but no standstill-like phases. Periodicity analysis using TESS data shows that superhumps can persist during both echo outbursts and standstill-like phases. Although standstills have previously been observed in AM CVn stars, the standstill-like phases we observe appear to represent a distinct phenomenon associated with post-superoutburst activity. We compare our results to other AM CVns that may exhibit similar behaviour.
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All authors Jan Kára, Liliana Rivera Sandoval, Iwona Kotko, Jean-Marie Hameury, Luis E. Salazar Manzano, Ryan J. Oelkers

High Energy Physics (Phenomenology)

Quasiparticle Modeling of Strongly Magnetized Strange Quark Systems

Yogesh Kumar, Manas Lohani, Poonam Jain et al. (+5 more)

We examine spin-polarized Strange Quark Matter and the complex structure of Strange Quark Stars in the existence of a strong magnetic field. Our framework uses a quasiparticle model, en hanced by a QCD-informed effective quark mass dependent on both chemical potential value and magnetic field strength. The resulting Equation of State yields an energy per baryon below the iron limit, supporting the hypothesis that the actual ground state of matter is strange matter. The Tolman-Oppenheimer-Volkoff expressions are solved and find that the maximum stellar mass decreases with the degree of spin polarization, reaching as high as 2.35 Mo with a related radius 12.33 km. Furthermore, the model predictions for mass, radius, and surface redshift are in excel lent conformance to observational limitations for the massive pulsar PSR J0952-0607. These results highlight the crucial role of quasiparticle medium effects and strong magnetic fields in describing dense matter.
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All authors Yogesh Kumar, Manas Lohani, Poonam Jain, Pargin Bangotra, Vinod Kumar, T. A. Nahool, Om Prakash, Sanjay Tyagi

Solar and Stellar Astrophysics

Understanding the Complex Morphology of a Coronal Mass Ejection. III: How to Create a Severe Geomagnetic Storm

Cecilia Mac Cormack, Abril Sahade, Erika Palmerio et al. (+4 more)

On April 21, 2023, a complex filament eruption produced an Earth-directed coronal mass ejection (CME) that triggered the first severe geomagnetic storm of solar cycle 25. The primary objective of this work is to understand the physical origin of the severe impact of this CME on Earth. We explore the CME's complex morphology by simulating the eruption using the thermodynamic magnetohydrodynamic (MHD) model CORHEL-CME. We model the pre-eruptive structure as two intertwined magnetic flux ropes and validate the early evolution of the event by comparing synthetic observables generated from the model with extreme-ultraviolet and white-light observations. We then compare the simulated CME structure with in situ measurements. From our analysis, we conclude that the CME merged with a stream interaction region (SIR) before reaching Earth. This interaction compressed the CME sheath, producing a sustained negative $B_n$ component that, together with the associated enhancement in solar wind density and velocity, triggered the geomagnetic storm. The internal configuration of the magnetic flux rope, which also maintained a sustained southward component during its propagation toward Earth, intensified the storm to severe levels. This model-data comparison underscores the power of using MHD simulations, when validated by multi-viewpoint observations, to reveal hidden dynamical processes and improve the understanding and prediction of space weather impacts.
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All authors Cecilia Mac Cormack, Abril Sahade, Erika Palmerio, Evangelia Samara, Phillip Hess, Robin C. Colaninno, Teresa Nieves-Chinchilla

Computational Physics

A deep energy method formulation for phase-field modelling of ductile fracture

Nojus Plungė, Peter Brommer, Rachel S. Edwards et al. (+1 more)

This work extends the Deep Energy Method to phase-field modelling of ductile fracture in elasto-plastic solids. Its key contribution is an incremental DEM-based formulation that couples history-dependent J2 plasticity and plasticity-dependent fracture toughness with separate energy-optimised displacement and phase-field representations. The formulation combines the second-order Ambrosio-Tortorelli phase-field fracture model with small-strain J2 plasticity and linear isotropic hardening. A volumetric-deviatoric split defines the elastic crack-driving energy, while accumulated equivalent plastic strain governs the degradation of local fracture toughness. Plastic internal variables are updated locally through radial return. The reduced energy is minimised alternately with respect to the displacement and phase fields, represented by a ReZero residual neural network and spatially localised Gaussian radial basis functions with trainable centres, respectively. This split addresses the diffuse phase-field profiles observed in preliminary calculations with a shared global network. Alternating optimisation is combined with transfer learning to reuse trainable parameters and optimiser states across loading increments, while the converged constitutive history is carried forward separately at quadrature points. The numerical results demonstrate close agreement with finite-element reference solutions in predicting force-displacement responses, energy evolution, plastic deformation and crack propagation. The framework captures the main features of ductile fracture, although accuracy becomes more sensitive to loading increments near abrupt fracture events.
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All authors Nojus Plungė, Peter Brommer, Rachel S. Edwards, Emmanouil G. Kakouris

Soft Condensed Matter

Geometry-Encoded Hidden Orientational Memory

Vladimir A. Baulin

Materials usually remember their past through dissipative changes of structure or through a net order. Simulations of caged colloidal ellipsoids at a fluid interface reveal a purely orientational memory. The particles stay in place, the layer has no net alignment, and a pattern written by a field is retained by capillary interactions between neighbors. It lasts hundreds of times longer than a particle takes to reorient, while every particle keeps rotating. The layer also remembers sequence: when two strong fields act one after the other on the same particles, it records which came last.
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Quantum Gases

Viscous hydrodynamics from correlated losses

Aleksandr N. Mikheev, Orjan Ameye, Oded Zilberberg et al. (+1 more)

Interactions turn a gas into a fluid. We show that two-body loss can take their place. Correlated loss induces elastic scattering, as required by the optical theorem, which dominates at strong loss via the quantum Zeno effect. A nondegenerate gas with only two-body loss thus flows hydrodynamically, with viscosity and thermal conductivity close to those of the unitary Fermi gas. As loss heats the gas, both grow in time with a universal exponent 3/8. Unlike single-particle loss, two-body loss can engineer collisions, and hence transport, in quantum matter.
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All authors Aleksandr N. Mikheev, Orjan Ameye, Oded Zilberberg, Jeff Maki

Earth and Planetary Astrophysics

Science-Driven Performance Requirements for UV Coronagraph Design: Implications for O$_3$ Detection in Earth-like Atmospheres

Amber V. Young, Giada Arney, Shawn Domagal-Goldman et al. (+6 more)

Detecting biosignatures on Earth-like exoplanets from the Proterozoic era requires instrumentation capable of probing near-ultraviolet (NUV) spectral features, particularly ozone (\ce{O3}), which serves as an indirect proxy for molecular oxygen (\ce{O2}) when direct detection is challenging. Using a combination of photochemical-climate modeling and atmospheric retrieval simulations, we quantify fiducial instrument performance requirements for robust \ce{O3} detection and assess the risk of spectral false positives from sulfur dioxide (\ce{SO2}). Our analysis demonstrates the \ce{O3} abundances for Proterozoic Earth-like planets with \ce{O2} as low as 0.1% the present atmospheric level, can be constrained to within an order of magnitude at 1\,$\sigma$ confidence using three adjacent photometric bandpasses at a signal-to-noise ratio of 10 at 0.366\,$\upmu$m, each with a 15% width, and a short wavelength cutoff for those observations near 0.26\,$\upmu$m. The self-consistent steady state atmospheric modeling results show that \ce{SO2} buildup is difficult in a habitable environment with appreciable amounts of water vapor in its atmosphere and would require volcanic outgassing rates at least two orders of magnitude above present-day Earth to reach surface abundance levels comparable to Proterozoic Earth-like abundances of \ce{O3}. Even under these high \ce{SO2} flux scenarios, \ce{SO2} remains largely unconstrained with the recommended observational configuration, reinforcing the need for NUV coverage in coronagraphic instruments. Our findings support the inclusion of UV-optimized optics and detectors on the Habitable Worlds Observatory (HWO) to enable biosignature detection strategies sensitive to atmospheric conditions across key phases of Earth's geological history.
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All authors Amber V. Young, Giada Arney, Shawn Domagal-Goldman, Tyler D. Robinson, Roser Juanola-Parramon, Christopher Stark, Renyu Hu, Armen Tokadjian, Mario Damiano

Astrophysics of Galaxies

MOSS III: MeerKATs view on the galaxy populations in two massive galaxy clusters

Robert Kincaid, Mark Sargent, Pascale Jablonka et al. (+5 more)

The MeerKAT Observations of the Saraswati Supercluster (MOSS) is an ongoing project attempting to study the radio and optical properties of the core region of the Saraswati supercluster (z = 0.28) and will eventually entail a full survey of the entire supercluster region. Here we use radio catalogs from previous deep pilot MeerKAT L-band (1.28 GHz) observations (angular resolution of 8 arcsec) of the core region of the Saraswati supercluster. The region hosts two galaxy clusters representing distinct environments: The most massive cluster Abell 2631, and the second most massive cluster ZwCl2341, that is significantly more dynamically active. The deep radio catalogs of these clusters were combined with spectroscopic redshifts (mainly from DESI DR1 and SDSS DR16) and optical photometry catalogs of the cluster member galaxy source population. We use these redshifts together with the 1.4GHz MeerKAT flux densities to derive the dust-free star-formation rate (SFR) and evaluate various trends in the radio SFG and AGN galaxy populations. We find that the actively merging cluster ZwCL2341 has an increased star-forming galaxy population compared to A2631 with up to 4 times more star-forming galaxies. When looking at SFG-related radio processes we see s enhanced SF-related activity in ZwCL2341 with SF-related radio processes dominates entirely over AGN-related radio processes. This suggests that dynamically active environments associated with cluster assembly, such as mergers, have enhanced SF radio-activity and increased SFG (both radio and non-radio) galaxy population compared to lesser active systems.
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All authors Robert Kincaid, Mark Sargent, Pascale Jablonka, Bruno Slaus, Viral Parekh, Shishir Sankhayan, Sameer Salunke, Jean-Paul Kneib

High Energy Physics (Theory)

Coherent states of neutrinos in rotating matter

Alexander Breev and Maxim Dvornikov

We study coherent states of neutrinos electroweakly interacting with rotating matter. We start with the Dirac equation for a massive neutrino propagating in background matter with a coordinate dependent effective potential. Then, we consider the limit of massless particles and the specific matter velocity profile. It allows us to reduce the neutrino Hamiltonian to the harmonic oscillator form. We find the exact solutions of the Dirac equation and construct the creation and annihilation operators. Using these results, we build the generalized coherent states of neutrinos. We provide the interpretation of these coherent states in terms of the classical physics. In particular, we demonstrate that the coherent states constructed approach plane waves in the limit of slow matter rotation. We also define the effective neutrino mass owing to the interaction of a massless neutrino with rotating matter. Then, we consider a special case of the generalized coherent states which are called the neutrino coherent states. The situation of the degenerate parameters of the system is also studied. Finally, we apply our results for astrophysical neutrinos propagating in dense matter of a rapidly rotating neutron star (NS). We calculate the effective neutrino masses for different neutrino energies for realistic parameters of NS.
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Quantum Physics

Federated Unlearning of Quantum Data via Classical Shadows

Zihao Ding, Jun Huang and Cong-cong Xing

Quantum federated learning trains a quantum neural network (QNN) across nodes that hold quantum data, such as the states of quantum sensors. To forget data, unlearning methods for quantum models replay them, and federated unlearning from stored updates removes whole nodes only. Quantum data cannot be replayed, since a state is consumed when measured and cannot be cloned. We propose Shadow-based Data Erasure (SHADE), in which each node records a classical shadow of every training state, a few randomized single-qubit measurements taken at training time. The gradient and curvature of a QNN on a state are expectations of observables, so SHADE estimates them for the forget data from the shadows at any later parameters and removes their effect by a federated Newton correction. Only classical estimates cross the network. We prove that the shadow size needed for a target unlearning error grows exponentially in the size of the backward light cone of the measured observable and not in the number of qubits. In simulation with 50 nodes and on edge boards, SHADE matches the forget accuracy of retraining within 0.5 points, without replay and in under 0.2 s.
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Quantum Physics

A modular quantum computer based on Cornucopia codes

Zhide Lu, Weikang Li, Yinghao Ma et al. (+5 more)

Ultra-high-rate quantum error correction codes store many logical qubits in a single code block with few physical qubits. A fault-tolerant quantum computer, however, also requires a universal set of logical operations on individually addressable logical qubits, and the ancilla overhead of these operations may erode the advantage of the high encoding rate. Here, we propose the Cornucopia architecture, in which a universal set of logical operations is implemented at low overhead for the Cornucopia codes. In particular, we focus on the [[2844,1426,18]] Cornucopia code as an example and introduce a modular quantum computer built from such code blocks connected by bridges. Each block stores 1,426 logical qubits and serves as a universal logical processor. Exploiting the code's translation symmetry, we construct a family of reusable gadgets that individually address 1,422 logical qubits within each block. These gadgets support three universal logical instruction sets: basic, high-throughput and fixed-extractor. Excluding magic-state factories, a module with sufficient workspace to execute any instruction in the basic set requires an average of 4.1 physical qubits per logical qubit, compared with 3.0 for memory alone. The architecture thus preserves the resource advantage of ultra-high-rate quantum memory while enabling universal logical computation, providing a route towards low-overhead fault-tolerant quantum computers.
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All authors Zhide Lu, Weikang Li, Yinghao Ma, Hanyu Yan, Bingrun Wang, Yixuan Ma, Zheng-Zhi Sun, Dong-Ling Deng

Instrumentation and Methods for Astrophysics

Neural networks applied to forecasting the astroclimatic and meteorological parameters in an operational context

C. Weinberger, E. Masciadri, M. De Sepibus et al. (+4 more)

Forecasting optical turbulence and atmospheric parameters is crucial for science operations of present and new generation ground-based telescopes (ELT) as well as for free-space optical communication (FSOC). These forecasts are also useful to optimize the AO use, particularly in the ELT framework too. Recent research has demonstrated that the AR technique currently provides the best performances in predicting atmospheric and astroclimatic parameters on a time scale of 1 hour (e.g., RMSE 0.1" for the seeing), however deep learning offers some intriguing features that include the high adaptability, the correlation that can be found between different parameters treated simultaneously and different architectures can explore the capability for possible improvements. For this reason, it is important to investigate on the possibility to improve forecast performances beyond the score achieved by AR or simply to apply deep learning in those context in which it is not possible to apply the AR. In this contribution we investigate a set of algorithms belonging to the family of the neural networks that in principle are more suitable than the Random Forest (RF) model for this kind of application. We address specific questions related to the forecast performances in operational configurations. Besides that, we also investigate the impacts on gaps on the trained data set due to the lack of measurements of the optical turbulence during the day time. We show evidences that with measurements covering the whole 24-hours forecast performances might improve. Our test has been done on the wind speed in this contribution. This work is done in the framework of the operational forecast system for LBT (ALTA Center) and for the VLT (FATE project) that are leaded by our team.
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All authors C. Weinberger, E. Masciadri, M. De Sepibus, A. Otarola, S. Miesske, C. Veillet, S. Ragland

High Energy Physics (Phenomenology)

Born-Oppenheimer chiral effective field theory and its application to $X_b$

Yu Zhang, Feng-Kun Guo, Christoph Hanhart et al. (+2 more)

Following the discovery of the exotic state $X(3872)$ in the charmonium spectrum, the possible existence of an analogous state, $X_b$, in the bottomonium sector has attracted considerable attention of the hadronic physics community. In this work, we lay the ground for the development of Born-Oppenheimer chiral effective field theory (BO$\chi$EFT), that allows us to include both quark and hadron degrees of freedom as well as the full complexity of the meson-exchange potential in a systematic way. For illustration, the formalism to leading order (LO) is applied to the system of $\chi_{b1}$ states and in particular the $X_b$. The two parameters that are present at this order are constrained using experimental information on the bottomonium spectrum together with lattice input on static quark-antiquark potentials, including string breaking effects. The framework identifies the observed $1^{++}$ state at 10.513 GeV with a predominantly molecular $X_b$, the bottom counterpart of the $X(3872)$, and predicts an additional predominantly compact bottomonium state at 10.544 GeV, about 60 MeV below the $B\bar{B}^*$ threshold.
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All authors Yu Zhang, Feng-Kun Guo, Christoph Hanhart, Alexey Nefediev, Paul Pütz

Mesoscale and Nanoscale Physics

Cooperative Boundary Switching of Mesoscopic Real Spectra in a Non-Hermitian Chain Family

Chengxi Li, Hao Zhu, Tie-Fu Zhang et al. (+1 more)

At fixed bulk criticality, every fixed nonsingular real single-end potential preserves a growing local population of real eigenvalues in an open analytic family of non-Hermitian chains. An open region of two-end real potentials removes this population. A boundary-amplitude criterion fixes the minimum number of controlled ends. The population grows as $\sqrt N$, where $N$ is chain length, although its normalized spectral weight vanishes and the local limiting bands remain unchanged. For a representative chain's four zero-detuning settings, an independent passive Hermitian double chain converts this distinction into separated resonances at one fixed local port under a common coupling scan at fixed probe carrier. Its absolute reflection contrast and stability margin both scale as $N^{-1}$, with explicit sufficient resource budgets. Boundary amplitudes thus fix a minimum control requirement that limiting bands and thermodynamic spectral density do not specify.
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All authors Chengxi Li, Hao Zhu, Tie-Fu Zhang, Wanzi Sun

Quantum Physics

The cost of classically simulating quantum communication is as high as it could be

Riccardo Castellano, Pavel Sekatski and Nicolas Brunner

A long-standing open question is to characterize the classical communication cost of simulating the correlations arising from measurements on finite-dimensional quantum systems. We consider this question in the prepare-and-measure scenario. First we construct a classical simulation model involving a finite average number of bits of one-way communication that simulates exactly the correlations arising from arbitrary $d$-dimensional quantum states and arbitrary measurements. Second, we show that no classical simulation protocol involving a finite average message dimension can exist for $d\geq 4$, hence strengthening a recent result of de Gois, Santos and Vieira. Our first result relies on a more general simulation theorem which can be applied to certain continuous variable (i.e. infinite-dimensional) quantum systems, and even beyond quantum theory, e.g. to generalized probabilistic theories. In particular, we show that multimode Gaussian states of bounded average energy and general Gaussian measurements admit an exact classical simulation with a finite expected number of bits. Overall, our results show that the classical simulation cost of quantum communication is essentially as high as it could be.
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Mathematical Physics · Cross-listed from stat.ML

Conformalized Physics-Informed Weak Regression for Parameter Estimation in Epidemic Models

Allan Peter Engsig-Karup

Compartment models of infectious diseases are often linear in coefficients that are physical parameters or products or ratios of them. We exploit this with closed-form least squares and equip the estimates with distribution-free uncertainty. Physics-informed regression (PIR) fits the parameters to finite-difference derivatives of the data; we introduce physics-informed weak regression (PIWR), which integrates the model in time instead, needs no derivatives of the data, estimates the initial state jointly and is high-order accurate. To quantify uncertainty we wrap both estimators in split conformal prediction, with a calibration population generated by the physics-based model itself, giving simultaneous intervals for all parameters with a finite-sample coverage guarantee. A residual-adaptive factor, computed without ground truth, scales the intervals to each data set (PIWR-RACC). On the eleven benchmark models of disease-informed neural networks (DINNs), PIWR or PIR-FD6 is one to four orders of magnitude more accurate than the reported DINN results wherever the sampling resolves the dynamics, in about a millisecond per fit instead of minutes to hours of training, and the 90% intervals achieve 87-92% coverage in all 88 settings. On the S3I3R model of the original PIR study, PIWR lowers the reported PIR errors by about three orders of magnitude. On real data from the 1978 boarding-school influenza outbreak, a variable-projection variant gives calibrated 95% intervals that overlap those of a Bayesian analysis. On a time-varying transmission benchmark, a B-spline expansion of beta(t) keeps PIR and PIWR linear; they are more accurate than physics-informed neural networks in three of four cases and comparable in the noisiest, with simultaneous bands for beta(t). The complete conformal calibration takes less than two minutes for every benchmark.
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Other Condensed Matter

A Conservative Darcy-Brinkman-Stokes Formulation for PHREEQC-Coupled Reactive Transport with Cell-Based Surface Complexation

Hannah P. Menke, Florian Doster and Julien Maes

We present a mass-conservative Darcy-Brinkman-Stokes (DBS) formulation for reactive transport with cell-based surface complexation in image-based porous media, coupled to PHREEQC and implemented in GeoChemFoam, an OpenFOAM-based toolbox. Dissolved species are transported in the physical mobile-water fraction, adsorbed species are stored as conservative cell-scale surface inventories, and each reactive cell is coupled to PHREEQC. Reactive surface area is prescribed independently as a cell field, so that internal area left unresolved by segmentation of microporous phases can be represented while DBS flow and transport are retained in the resolved pore space. The implementation is verified with a test suite that isolates the coupling of transport and chemistry from the construction of reactive surface area. Aqueous and adsorbed mass balance is evaluated against a one-dimensional analytical retardation benchmark and closed-system batch calculations. The smooth-interface surface-area algorithms are tested on idealised two- and three-dimensional geometries. In a two-scale lithium micromodel, DBS reproduces fully resolved aqueous and sorbed inventories within 0.6% across Pe=0.1-10. The applications comprise Pb2+ retardation by hydrous ferric oxide coatings in a two-dimensional fracture network, competitive Mn2+/Mg2+ exchange in a three-dimensional Kelvin-cell sorbent, and Sr2+/Ca2+ exchange in Estaillades limestone. In the fracture-network and limestone cases, the formulation yields spatially resolved aqueous and adsorbed inventories even where reactive surface area is only partly resolved at the image scale. The framework therefore supports conservative surface-complexation modelling in both resolved and unresolved pore structures, with relevance to contaminant retention, selective ion capture, and radionuclide transport.
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Fluid Dynamics

Retraction of a liquid drop in a Hele-Shaw cell

Luke Neville and Paul R. Kaneelil

When a long liquid drop is confined in a Hele-Shaw cell, the pull of surface tension produces a rapid retraction of its tip, causing it to bulge out as it draws up the excess liquid. Using numerical simulations, we demonstrate that this retraction is self-similar at long times, with the speed of retraction slowing like $t^{-1/2}$, where $t$ is the duration of retraction. After showing how this scaling can be understood using force and mass balance, we perform an asymptotic analysis of the Hele-Shaw equations to derive both the shape of the retracting drop, as well as prefactors of the scaling laws. Excellent agreement is found between our simulations and theory, and the experimental consequences are pointed out.
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Atomic Physics

Photoemission study of Iodoalkanes

Maximilian Forster, Maximilian Pollanka, Sven-Joachim Paul et al. (+7 more)

Core level atomic photoionization is influenced by the molecular environment of the emitting atom. To probe this influence we used extreme ultraviolet (XUV) radiation to measure the I$\left(4d\to\varepsilon f \right)$ photoemission of four iodine substituted alkanes in the range from 60 eV to 160 eV photon energy. Using two detection angles relative to light polarization allowed us to extract and compare the asymmetry parameter of the investigated compounds. These results are in agreement with theory by Pi and Landsman (L.-W. Pi and A. Landsman, Attosecond time delay in photoionization of noble-gas and halogen atoms, Applied Sciences 8, 322 (2018)) and previous experiments by Olney et al. (T. N. Olney, G. Cooper, and C. Brion, Quantitative studies of the photoabsorption (4.5-488 ev) and photoionization (9-59.5 ev) of methyl iodide using dipole electron impact techniques, Chemical Physics 232, 211 (1998)) for iodomethane. 2-iodopropane behaves nearly identical to iodomethane, while for iodoethane and 1-iodopropane we find a distinct and consistent, energy dependant difference most prominent at around 130 eV photon energy. This further proves the influence of the chemical environment on core level photoionization. Due to the sensitivity on the exact positions of the carbon atoms and the energy dependence we hypothesise this difference is caused by intramolecular scattering of the outgoing photoelectron wave packet, causing changes in the angular distribution.
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All authors Maximilian Forster, Maximilian Pollanka, Sven-Joachim Paul, Pascal Freisinger, Christian Schröder, Robert Richter, Michele Alagia, Alessio Bruno, Stefano Stranges, Reinhard Kienberger

Quantum Physics

The Generalized BEADS Representation: An Informationally Complete Visualization of Mixed Quantum States

Celina Bräutigam, Steffen J. Glaser and Dennis Huber

A deep understanding of quantum information theory is essential for quantum science and technology. However, quantum mechanics and particularly quantum information theory suffer from a lack of intuitive images. Visualization tools offer novel perspectives on many problems in quantum physics by revealing important properties of quantum states and processes that are otherwise obscured by abstract mathematical formalisms. Here, we extend the previously established BEADS representation of pure states to the so-called generalized BEADS representation of mixed quantum states. We introduce spherical functions, so-called beads to visualize correlation structures of mixed quantum states. A recursive optimization scheme is used to obtain minimum-entanglement pure state decompositions of all subsystems of a given N-qubit state. We show how correlation function components can be decomposed into individual contributions that directly correspond to different types of correlations of mixed states. This allows us to visually characterize the total correlation, genuine n-partite entanglement, nonclassical quantum-discord-type correlations as well as classical correlations. After outlining the mathematical details relevant for constructing the representation, we examine the generalized BEADS representations for various classes of mixed states including product, classically correlated, separable but nonclassically correlated, as well as entangled states. As exemplary applications of the generalized BEADS representation, we showcase entanglement distillation and the effects of noise channels.
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Cosmology and Nongalactic Astrophysics

The Atacama Cosmology Telescope: DR6 Constraints on Isotropic Time-Dependent Cosmic Birefringence from Axion-like Particles

Zachary B. Huber, Huajian Yang, Steve K. Choi et al. (+7 more)

Axion-like particles (ALPs) with sufficiently low masses are dark matter candidates because they could account for much or all of the observed dark matter energy density and help explain observations of galactic substructure. Such pseudoscalar fields could couple to photons, causing a time-dependent rotation of the polarization of the light with an oscillation frequency equal to the ALP mass. We use measurements of the polarization of the cosmic microwave background (CMB) by the Atacama Cosmology Telescope (ACT) between 2017 and 2022 to search for this effect using an EB power spectrum estimator. By probing oscillation periods from days to years, the data constrain the coupling between ALPs and photons for ALP masses between $2.5\times 10^{-23}$ eV and $4.8\times 10^{-20}$ eV. We find no evidence for such a signal and set a 95% upper bound on the axion-photon coupling constant, $g_{\phi\gamma} < 1.1\times10^{-11}\left({m_\phi}/{10^{-21}\,\mathrm{eV}}\right)\,\mathrm{GeV}^{-1} .$ This limit assumes that ALPs make up all of the dark matter and that the ALP field amplitude is stochastically distributed, which leads to more conservative bounds than the deterministic-field assumption used in some previous CMB polarization analyses. Among searches for ALP-photon coupling using CMB polarization, we set the strongest bounds to date under the stochastic-field assumption. This work develops a methodology to analyze over 10,000 time-sliced "depth-1" polarization maps from ACT, a data product that will be standard for time-domain astrophysics with the Simons Observatory, enabling searches with a higher sensitivity and observing span.
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All authors Zachary B. Huber, Huajian Yang, Steve K. Choi, Erminia Calabrese, Vera Gluscevic, Sigurd Naess, Michael D. Niemack, Lyman A. Page, Alexander van Engelen, Edward J. Wollack

Mathematical Physics · Cross-listed from math.AG

Reversible Higgs Bundles

Krishnendu Gongopadhyay and Tathagata Nayak

We study reversible Higgs bundles on a compact Riemann surface $\Sigma$ of genus $g\geq 2$, that is, $G$-Higgs bundles $(E,\Phi)$ with $(E,\Phi)\cong(E,-\Phi)$. For a complex reductive group $G$ realized as a self-adjoint subgroup of $GL(n,\mathbb{C})$, we show that if $(E,\Phi)$ corresponds to a representation $\rho$ of $\pi_1(\Sigma)$, then $(E,-\Phi)$ corresponds to $(\overline{\rho}^{\,t})^{-1}$. As a consequence, the moduli space of reversible Higgs bundles is the fixed locus of an involution of the character variety and carries the structure of a real affine algebraic set. For a connected semisimple group and every topological type, we prove that the reversible locus in the smooth moduli space is a $(B,A,A)$-brane. We then describe reversibility through spectral data: in even rank, for a smooth spectral curve, reversible Higgs bundles correspond to line bundles invariant under the involution $\eta\mapsto-\eta$; in odd rank, under natural genericity assumptions for which the spectral curve is nodal, we give a gluing criterion together with an explicit polystability condition. Finally, for $SL(2n,\mathbb{C})$ we construct a relative Fourier–Mukai transform over the regular locus of the Hitchin base and prove that it maps the structure sheaf of the reversible locus to an object whose support is exactly the regular degree-zero $PSp(2n,\mathbb{C})$-locus in the Langlands dual $PGL(2n,\mathbb{C})$-moduli space. This support is of type $(B,B,B)$.
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Quantum Physics

Logical gate set tomography

Piper C. Wysocki, Juan Gonzalez De Mendoza, Karl Mayer et al. (+11 more)

Quantum error correction (QEC) can strongly suppress noise, but predicting whether a computation succeeds requires understanding not only how much effective noise persists after QEC, but what form that noise takes. To thoroughly characterize this noise, we introduce logical gate set tomography (“logical GST”). Logical GST produces detailed representations of noisy logical operations that can be used to derive higher-level metrics, such as gate fidelity and diamond distance, and to test for non-Markovian and coherent logical errors. We use logical GST to obtain the first full, self-consistent characterization of a universal single-qubit logical gate set, implemented in the seven-qubit Steane code using Quantinuum System Model H1, a 20-qubit trapped-ion quantum processor. In the experimental data from H1, logical GST identified predominantly logical Pauli-stochastic errors, found no evidence of logical non-Markovianity, and detected weak potential signatures of coherent logical error. By contrast, higher-shot datasets generated with Quantinuum's detailed system emulator, identify mechanisms for weak but statistically significant logical non-Markovianity and strong evidence of coherent logical error. Finally, we use logical GST to perform error attribution with the system emulator, revealing how specific physical error sources shape logical error mechanisms.
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All authors Piper C. Wysocki, Juan Gonzalez De Mendoza, Karl Mayer, Natalie C. Brown, Ciaran Ryan-Anderson, Jalan A. Ziyad, Jordan H. Hines, Daniel G. Hothem, Corey I. Ostrove, Timothy J. Proctor, Kevin C. Young, Robin J. Blume-Kohout, Charles H. Baldwin, Kenneth M. Rudinger

Solar and Stellar Astrophysics

Velocity-field estimation techniques for on-disk solar coronal bright fronts (CBFs) and shock-wave propagation

Oleg Stepanyuk and Kamen Kozarev

Coronal mass ejections (CMEs) are large expulsions of plasma and magnetic fields from the solar corona into the heliosphere. Coronal shock waves are driven by CMEs, and accurate Solar Energetic Particles (SEP) forecasting requires knowing when and where shocks form, how fast they propagate, and how they interact with the coronal magnetic field. By measuring the speed, geometry and temporal evolution of coronal bright fronts (CBFs), one can create more realistic predictions of SEP onset and intensity at Earth, thus velocity-field estimation techniques supply these critical parameters. High-resolution velocity field maps can provide even deeper insight. Instead of yielding only an overall speed of the front, techniques like FLCT and optical flow can show the spatial distribution of velocities across the entire wave dome or front. These analyses reveal which parts of the front are moving fastest and how the front might be deforming as it expands. Here we discuss a set of practical parameters for Lucas–Kanade, Horn–Schunck, FLCT, and Farneback algorithms, arrived at by combining analytic reasoning with empirical measurements on a single event—and demonstrate the potential of these techniques for on-disk shock-wave propagation during the X1.5-class event that took place 10 May 2022, processed by the wavelet-based Wavetrack technique. A better understanding of how to fine-tune these parameters could improve the precision of algorithms running in pipelines, and is especially valuable where per-event hand-tuning is impractical.
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