Mesoscale and Nanoscale Physics
Plasmon modes in tilted three-dimensional nodal-ring semimetals. I. $\mathcal{PT}$-symmetric nodal ring and its gapped cousin
Ipsita Mandal
We study collective charge excitations in three-dimensional $\mathcal{PT}$-symmetric nodal-ring semimetals (PTNRs) and their gapped counterparts (GNRs) in the presence of band tilt, together with Weyl semimetals (WSMs). Within a low-energy two-band description, we consider untilted systems as well as in-plane and axial tilts. Using the random-phase approximation, we obtain the density of states, Drude weights, dielectric functions, and plasmon dispersions at low doping and in the intrinsic limit. The mass gap and the two inequivalent tilt directions generate distinct
Fermi-surface
topologies and thereby control the formation and damping of plasmons. By comparing the collective modes with the particle-hole continuum, we identify the regimes in which plasmons remain well defined. We also calculate the response of untilted and tilted WSMs and contrast it with that of PTNRs and GNRs. The two classes of semimetals differ in the carrier-density dependence and isotropy of the plasmon frequency as well as in interband screening and their response to tilt. These differences reflect their distinct
Fermi-surface geometries and interband structures. Our results establish how mass and tilt govern collective charge dynamics through their interplay with intraband spectral weight and interband particle-hole excitations.
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Lattice Field Theory
The Peskin-Takeuchi $S$ parameter and vector meson decay constants in $N_f=8$ QCD
Yasumichi Aoki, Tatsumi Aoyama, Ed Bennett et al. (+7 more)
We use
lattice gauge theory to investigate the Peskin-Takeuchi S parameter in SU(3) gauge theory with eight light fundamental
fermions (eight-
flavor QCD), a candidate for walking technicolor. We develop a new approach to computing S using the first time moment of current correlators, in addition to the conventional
vacuum-polarization method, and obtain consistent results. Finite-volume (FV) corrections are estimated using data at multiple
lattice volumes and a formula motivated by
chiral perturbation theory. At the smallest
fermion mass, the one-doublet contribution is S = 0.281(5)(17), smaller than the value $\sim 0.35$ in scaled-up 2+1-
flavor QCD (without subtracting the SM contribution). However, contrary to naive expectations, S toward smaller
fermion masses is not necessarily suppressed once FV corrections are included. The resulting Gasser-Leutwyler parameter $L_{10}^r(M_\rho)$ is similar to that in real-world QCD. We also determine the vector and axial-vector
meson decay constants, $F_\rho$ and $F_{a_1}$. The ratio $F_\rho/F_\pi$ is stable against the
fermion mass and consistent with the KSRF estimate, implying a $\rho\pi\pi$ coupling similar to that in real-world QCD. We predict the techni-rho decay width into weak
bosons to be $\Gamma_\rho/M_\rho \lesssim 0.24/N$, where N is the number of weak doublets. We further find that the rho- and $a_1$-dominated Weinberg spectral-function and Das-Mathur-Okubo sum rules are satisfied, yielding S and $L_{10}^r(M_\rho)$ consistent with our main results. We discuss implications for BSM model building.
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All authors Yasumichi Aoki, Tatsumi Aoyama, Ed Bennett, Toshihide Maskawaa, Kohtaroh Miura, Hiroshi Ohki, Enrico Rinaldi, Akihiro Shibata, Koichi Yamawaki, Takeshi Yamazaki
Materials Science
Machine-learning-guided exploration of domain walls in the hybrid improper ferroelectric Ca3Ti2O7
Ida C. Skogvoll, Erik Fransson, Leo Ö. Westin et al. (+4 more)
Ruddlesden-Popper phases are highly tunable and naturally layered structures, in which polarization can arise via a hybrid improper ferroelectric mechanism. This enables a complex domain wall (DW) structure where multiple order parameters, like octahedral rotations, polar distortions and strain, interact. In this work, we explore the rich set of DW structures in prototypical Ca3Ti2O7, mapping out the DWs in the {100}, {110} and {001} pseudo-tetragonal planes using group theory and machine-learned interatomic potentials (MLIPs). The trained potential reproduces the density functional theory (DFT) order parameter and polarization profiles for all wall types and orientations considered. A charge-aware training framework combined with reference Born effective charges reduces the prediction errors for the DW formation energies by 70%, revealing the importance of including long-range electrostatics to model
symmetry-broken interfaces. Finally, the MLIP is used to identify minimum energy pathways at the atomic scale with nearly the precision of DFT calculations, revealing a low-energy antipolar configuration for polarization switching.
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All authors Ida C. Skogvoll, Erik Fransson, Leo Ö. Westin, Benjamin A. D. Williamson, Nicholas C. Bristowe, Sverre M. Selbach, Paul Erhart
High Energy Physics (Phenomenology)
Resummation-scale uncertainties in PDF determinations
Hamed Abdolmaleki, Valerio Bertone, Giuseppe Bozzi et al. (+7 more)
We investigate the impact of resummation-scale variations on parton distribution function (PDF) determinations. These variations introduce an additional source of theoretical uncertainty related to the
evolution of PDFs and strong coupling $\alpha_s$ that has never previously been accounted for in PDF fits. Using the open-source xFitter framework, we quantify this uncertainty in fits to HERA deep-inelastic scattering data and examine its implications for predictions of top-
quark pair production at the LHC. We show that the resulting resummation-scale uncertainties have a sizable impact on LHC observables, highlighting the importance of including this source of uncertainty in precision QCD analyses.
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All authors Hamed Abdolmaleki, Valerio Bertone, Giuseppe Bozzi, Francesco Giuli, Alexander Glazov, Valentina Guglielmi, Francesco Hautmann, Fred Olness, Pavel Starovoitov, Oleksandr Zenaiev
Astrophysics of Galaxies
Extreme MgII Emission in Recently-Quenched Galaxies: A New Sample of Intermediate-Redshift Post-Starburst Quasars from the DESI Early Data Release
Margaret E. Verrico, Aayan Verma, K. Decker French et al. (+8 more)
Post-starburst
galaxies are
galaxies which have recently and rapidly shut off
star formation. AGN activity is often invoked to explain this rapid quenching, but most post-starburst selection methods select against optical AGN, motivating searches for "post-starburst
quasars." We present DESI observations of ten post-starburst
quasars with significant MgII emission ($L_{\text{MgII}} \geq 3 \times 10^{41}$ erg/s). This is the first sample of post-starburst
quasars to be selected from a post-starburst
galaxy parent sample rather than a
quasar catalog.
Quasars make up $4.6^{+1.6}_{-1.2}\%$ of the post-starburst parent sample at $0.49 \leq z \leq 1.39$. Using multiwavelength AGN diagnostics, we find that $26^{+3.0}_{-2.8}\%$ of post-starbursts in the parent sample host AGN. We find that post-starburst selection methods are biased against AGN with $\text{L}_{\text{Bol}}\gtrsim10^{45} \textrm{erg s}^{-1}$, potentially removing the
quasars responsible for driving
outflows that aid in quenching. Finally, we find that 9/10 post-starburst
quasars in our sample have no detected broad H$\beta$, similar to so-called "MgII emitters" that may be the remnants of fading
quasars; if confirmed, these objects suggest a link between post-starburst
galaxies and variable AGN. Our new sample of post-starburst
quasars provides a link between previously reported local and high
redshift post-starburst
quasars during the epoch when
star formation throughout the universe was declining.
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All authors Margaret E. Verrico, Aayan Verma, K. Decker French, David J. Setton, Omar Almaini, Jenny E. Greene, Stephanie LaMassa, Yuanze Luo, Pallavi Patil, Kate Rowlands, Dharlenny Soto
Quantum Physics
Zero Knowledge Proofs in Quantum Networks
Tuhin Paul, Srijani Das, Manasi Patra et al. (+1 more)
Zero-knowledge proofs (ZKPs) enable the verification of a statement without revealing any information beyond its validity and constitute a fundamental primitive in cryptography and information theory. However, existing constructions rely on computational assumptions and are predominantly confined to bipartite settings, leaving their information-theoretic realization in bipartite or network scenarios largely unexplored. Here we develop a framework for zero-knowledge verification based on the indistinguishability of
quantum states under operational constraints. Exploiting the fundamental limitations imposed by local operations, we show that a verifier is inherently restricted from extracting information about the underlying state while retaining the ability to verify correctness. We construct explicit protocols for multiparty
quantum networks that achieve information-theoretic security, ensuring that no subset of collaborating parties can gain knowledge beyond the validity of the statement, independent of their joint computational power.
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All authors Tuhin Paul, Srijani Das, Manasi Patra, Ramij Rahaman
Astrophysics of Galaxies
ViCTORIA project: A pilot study of the M49 region in the Virgo cluster in polarisation
A. Spasic, A. Benati, M. Brüggen et al. (+7 more)
Large-scale
magnetic fields permeate the Intracluster Medium (ICM) of
galaxy clusters. Understanding these fields gives an insight into the origin of
cosmic magnetic fields and the interaction of cluster
galaxies with the ICM. Using MeerKAT observations of the Virgo cluster as part of the ViCTORIA project, we probe
magnetic fields via Rotation Measure (RM) synthesis. The aim of this work is to characterise the
magnetic fields in and around the infalling group M49 in the Virgo cluster. We will probe the interaction of M49 with its surrounding medium through its imprint on the polarised emission and Faraday rotation. We use L-band MeerKAT data in full polarisation calibrated with the ViCTORIA MeerKAT Survey (ViMS) pipeline, which is designed for the calibration, imaging, mosaicking and RM Synthesis of the fields in the Virgo cluster, to achieve high-fidelity reconstruction of, both, total intensity and polarised emission. We analyse the background sources of the cluster for potential local changes in the
magnetic field, by calculating the RM distribution. In the final polarised image, consisting of four pointings of 45 min, we reach a noise level of $23.3 \mu \textrm{Jy/beam}$. We detect 101 background sources in the $\sim 2.5\, \textrm{deg}^2$ region around M49, corresponding to a source density of 40 sources/$ \textrm{deg}^2$. Across the $112\, \textrm{deg}^2$ observations of the Virgo cluster, this implies a total number of 4000 polarised sources. In M49 we find structured, diffuse polarised emission extending in the direction of the total intensity
radio tails. A higher polarisation fraction across the upper edge of the source indicates the effect of
magnetic field draping. Around M49 we find a larger RM scatter (at $3.8\sigma$) in the wake of M49 compared to the region in front of it. This can inform the modelling of the
turbulence created by
galactic motions.
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All authors A. Spasic, A. Benati, M. Brüggen, H. W. Edler, F. De Gasperin, V. Gustafsson, P. Serra, A. Bonafede, A. Boselli, H. McCall
Quantum Physics
Distributional Variants of the Aaronson-Ambainis Conjecture
Uma Girish, Kunal Mittal, Barak Nehoran et al. (+1 more)
A longstanding
conjecture in
quantum complexity theory asserts that, under the uniform input distribution,
quantum query
algorithms can be polynomially simulated by classical query
algorithms. More precisely, the acceptance probability of any
quantum query
algorithm can be approximated, on average over uniformly random inputs, by a classical query
algorithm, with only
polynomial query overhead. The
conjecture is central to understanding whether exponential
quantum advantages for decision problems necessarily rely on additional structure. We study analogues of this
conjecture under other natural input distributions and prove that they are all equivalent to the original uniform-distribution
conjecture. We first consider the product distribution $\mu_p$, where the input bits are independent Bernoulli variables with fixed bias $p$. We show that for every fixed $p \in (0, 1)$,
quantum query
algorithms under the $\mu_p$ distribution admit
polynomial-overhead classical simulations if and only if the same holds under the uniform distribution. Second, we consider the distribution $\nu_p$ that is uniform over the slice of strings with Hamming weight $\lfloor pn \rfloor$ and prove a similar equivalence for the $\nu_p$ distribution and the uniform distribution. The Aaronson-Ambainis
conjecture is a stronger statement that implies the above-mentioned
conjecture and is formulated in terms of bounded low-degree
polynomials on the Boolean hypercube. It asserts that under the uniform distribution, any such
polynomial with nonnegligible variance must have an influential variable. We formulate analogues of this
conjecture, where the underlying distribution is a biased product distribution or a uniform distribution over a slice, and prove that all these variants are equivalent to the original Aaronson-Ambainis
conjecture.
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All authors Uma Girish, Kunal Mittal, Barak Nehoran, Ran Raz
Optics
Contactless Continuous-Variable Quantum Optical State Conditioning With Classical MmWave Phase
Niloy Ghosh and Sarang Pendharker
This paper establishes the Heisenberg's picture framework for seamless mmWave-to-photonic data transduction. Based on this framework, contactless modulation of continuous-variable (CV)
quantum optical states with digitally modulated classical mmWave beams is shown for the first time. Our analysis reveals the direct influence of mmWave phase variation on the Wigner-space
evolution of modulated optical coherent and squeezed states. Furthermore, the analysis indicates that classical mmWave phase not only governs the displacement but also modulates the quadrature uncertainty of squeezed states, revealing a novel technique for
embedding information onto multiple
quantum-optical degrees of freedom. This work builds the theoretical and analytical foundation for wireless conditioning of
quantum light without conventional on-chip metallic interconnects and complex electronic control circuitry, thereby opening a key pathway toward seamless bridging of integrated
quantum photonics with emerging mmWave or THz communication technology.
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Disordered Systems and Neural Networks · Cross-listed from cs.LG
Weighting Schedules Govern What and When Score-Based Generative Models Learn from Multimodal Data
Jérémie Klinger, Raphaël Urfin, Giulio Biroli et al. (+1 more)
Score-based generative models generate new samples by integrating a time-dependent drift that carries Gaussian noise onto the target distribution. In practice this drift is modeled by a neural network, trained on a loss integrated over time $t$ with a weighting schedule $w(t)$. Along the backward dynamics, and for multi-modal distributions, trajectories commit to modes of the target within a narrow time window, the speciation time. In this work, focusing on high-dimensional data, we decompose the integrated loss into its single-time contributions and analyze each at fixed signal-to-noise ratio $\Lambda(t)$: we show that $\Lambda(t)$ sets the rate at which each feature of a
multimodal target - the mode directions and their relative weights - is acquired during training. Crucially, at high $\Lambda(t)$ all mode directions are acquired together, on a single timescale insensitive to their amplitudes, while the relative weights are not learned at all. Only near the speciation time, where $\Lambda(t)$ becomes of order one, do all features become learnable, each on its own timescale: the weights are acquired jointly with the directions, and the directions at rates set by their relative amplitudes. For models trained on time-integrated objectives, the learning dynamics is then governed by how much of the weighting effectively sits near the speciation time, which provides insights on $w(t)$ design choices. These results follow from an exact high-dimensional analysis of the training dynamics of unbalanced and hierarchical Gaussian mixtures. Numerical experiments on image and human genome haplotype generation recover the predicted hierarchy of learning timescales in more complex settings.
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All authors Jérémie Klinger, Raphaël Urfin, Giulio Biroli, Marylou Gabrié
High Energy Physics (Phenomenology)
System-size dependence of jet quenching from light to heavy-ion collisions at LHC
Man Xie, Xiang-Yu Wu, Han-Zhong Zhang et al. (+1 more)
Single inclusive
hadron suppression in high-energy heavy-ion collisions provides a sensitive probe of parton energy loss and jet transport coefficient in
quark-
gluon plasma (QGP). System size dependence of jet quenching can provide further constraints on the dynamics of jet quenching and parton energy loss. Motivated by recent experiments on light-ion collisions at the Large
Hadron Collider (LHC), we perform a systematic study of single-inclusive
hadron suppression in O+O, Ne+Ne, Xe+Xe and Pb+Pb collisions at the LHC energies. The calculations are carried out within the next-to-leading-order perturbative QCD model, incorporating the
nuclear modified initial-state parton distributions, final-state parton energy loss in the higher-twist approach and the temperature dependence of the jet transport coefficient $\hat q/T^3$ from the
Bayesian analyses of previous experimental data at the Relativistic Heavy-ion
Collider (RHIC) and LHC. Our model calculations can simultaneously describe the measured single-inclusive charged
hadron $R_{AA}$ in O+O, Ne+Ne, Xe+Xe and Pb+Pb collisions over a broad range of event centralities and in the minimum-bias events. We further illustrate the system size dependence of jet quenching through the ratio $R_{\mathrm{NeNe}}/R_{\mathrm{OO}}$ and the modification factors $R_{AA}$ as a function of $\langle N_{\mathrm{coll}} \rangle$ which follow a common behavior at fixed $p_{\rm T}$, indicating the formation of QGP even in the smallest collision systems.
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All authors Man Xie, Xiang-Yu Wu, Han-Zhong Zhang, Xin-Nian Wang
Cosmology and Nongalactic Astrophysics
LISA bright sirens as a tiebreaker among cosmologies in tension
M. F. A. Medeiros, F. C. Carvalho and L. L. Sales
Gravitational waves from massive black hole binaries detected by LISA will deliver luminosity distances without any astrophysical calibration, offering a probe of the expansion history independent of the
cosmic distance ladder. Rather than asking how tightly LISA will constrain a single fiducial cosmology, we ask which of several mutually discrepant present-day cosmologies a future LISA
dataset would render most self-consistent. We build mock catalogues of LISA bright sirens under three fiducial cosmologies drawn from
datasets that participate in the current $H_0$ discrepancy (Planck 2018, Union3 and Pantheon+SH0ES), with a self-consistent error budget from instrumental noise, weak
lensing and host peculiar velocities. We compare the posterior from the simulated LISA data alone with that of a real-data combination of Type Ia
supernovae, DESI
baryon acoustic oscillations,
cosmic chronometers and the compressed Planck 2018 CMB, and quantify their internal tension in the $(H_0,\Omega_m)$ plane, crossing each fiducial with three SN Ia compilations. The fiducial drives the tension, from $2.08\sigma$ to well beyond $5\sigma$, while the
supernova compilation changes it by at most $1.2\sigma$. The discriminating power is strongly asymmetric: a Pantheon+SH0ES universe is inconsistent with every background we test, at a significance far in excess of $5\sigma$ and still at $3$-$5\sigma$ for the $10$-$20$ events expected from recent population models, whereas the Planck 2018 and Union3 fiducials, which differ by only $0.24$ km/s/Mpc in $H_0$, cannot be separated by any catalogue size. LISA bright sirens are therefore a sharp arbiter of the Cepheid-calibrated scenario and, on this error budget, silent between the other two.
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Physics and Society
Structure of Exposure Modeling of Systems to Climate Change Related Hazards
Matthieu Dutel, Adam Abdin, Didier Soto et al. (+1 more)
Physical infrastructures designed for stable
climate conditions support a significant portion of daily human life activities. However,
climate change reshapes the distributions of extreme
climate intensities. As a result, physical infrastructures that may face extreme events exceeding their design thresholds risk damage and require adaptation. A preliminary step to adaptation is to identify exposed infrastructures to
climate hazards. This paper aims to structure the exposure modeling to
climate change hazards by providing an overall methodology. This paper instantiates a framework using the Boolean Exposure Model to assess how physical systems may be exposed to
climate hazards. The framework combines a Boolean System Model for infrastructures and a Boolean Hazard Model informed by extreme value statistics. An illustrative case study quantifies the exposure of road bridges in French administrative units to extreme temperatures. Results indicate increasing exposure across future
climate scenarios and time periods, with spatial non-uniformity. This framework supports multi-level analysis and integrates non-stationary
climate extremes, providing a structured exposure model to facilitate the adaptation of physical systems to
climate change.
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All authors Matthieu Dutel, Adam Abdin, Didier Soto, Anne Barros
Astrophysics of Galaxies
The 2MIG isolated AGNs – 4. Linking hot-dust reverberation to spectroscopically predicted BLR scales in IC~5287 and Mrk~845
I.O. Izviekova, I.B. Vavilova, O.V. Kompaniiets et al. (+2 more)
We investigate the relation between directly measured hot-
dust reverberation scales and spectroscopically predicted broad-line region (BLR) scales in the isolated Seyfert
galaxies IC~5287 and Mrk~845 (MCG+09-25-022), combining ZTF optical light curves, WISE/NEOWISE monitoring, and archival SDSS spectroscopy. Both
nuclei show BWB optical variability, RWB MIR behaviour, and delayed MIR responses consistent with circumnuclear
dust reprocessing. For IC~5287, interpolated cross-correlation function analysis with flux-randomisation/random-subset-selection uncertainties yields a rest-frame W1 delay of $106_{-39}^{+24}$~d, corresponding to $0.089_{-0.033}^{+0.020}$~pc. The median W2 response occurs at a longer delay, but the lag distributions overlap substantially. The SDSS decomposition reveals strong host dilution and BLR reddening, $E(B-V)_{\rm BLR}=0.612_{-0.066}^{+0.067}$~mag. Applying the same colour excess to the AGN continuum as an illustrative scenario increases the predicted H$\beta$ BLR lag from approximately 4.8 to 11.7~d and reduces the
dust-to-predicted-BLR radius ratios from approximately 20–25 to 8–10. For Mrk~845, transfer-function modelling gives a rest-frame W1 delay of $157_{-8}^{+19}$~d, corresponding to $0.132_{-0.007}^{+0.016}$~pc. Its W2 response occurs at a longer delay, with $P(\tau_{\rm W2}>\tau_{\rm W1})=0.963$, supporting wavelength-dependent hot-
dust structure. The SDSS spectrum shows more moderate BLR reddening, $E(B-V)_{\rm BLR}=0.197_{-0.039}^{+0.046}$~mag. The comparatively large
dust-to-predicted-BLR radius ratios in both
galaxies therefore primarily reflect the spectroscopically predicted BLR scales. These results emphasise the need to distinguish directly measured
dust reverberation radii from BLR radii inferred from single-epoch spectroscopy when interpreting the BLR–
dust hierarchy.
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All authors I.O. Izviekova, I.B. Vavilova, O.V. Kompaniiets, O. Zamora, R. Clavero
Chemical Physics
Experimental and numerical study of shock wave propagation in water generated by pulsed arc electrohydraulic discharges
Wen Chen, Olivier Maurel, Christian La Borderie et al. (+6 more)
The objective of this study is to simulate the propagation of the shock wave in water due to an explosion. The study is part of a global research program on the development of an alternative stimulation technique to conventional hydraulic fracturing in tight gas reservoirs aimed at inducing a distributed state of microcracking of rocks instead of localized fracture. We consider the possibility of increasing the permeability of rocks with dynamic blasts. The blast is a shock wave generated in water by pulsed arc electrohydraulic discharges. The amplitude of these shock waves is prescribed by the electrohydraulic discharges which generate high pressures of several kilobars within microseconds. A simplified method has been used to simulate the injected electrical energy as augmentation of enthalpy in water locally. The finite element code EUROPLEXUS is used to perform fluid fast dynamic computation. The predicted pressure is consistent with the experimental results. In addition, shock wave propagation characteristics predicted with simulation can be valuable reference for design of
underwater structural elements and engineering of
underwater explosion.
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All authors Wen Chen, Olivier Maurel, Christian La Borderie, Thierry Reess, Antoine Silvestre de Ferron, Mohammed Matallah, Gilles Pijaudier-Cabot, Jacques Antoine, Franck Rey-Bethbeder
High Energy Physics (Phenomenology)
Purely flavon driven leptogenesis for exactly degenerate Dirac or Majorana neutrino mass matrix in the type-I seesaw model
Yan Shao and Zhen-hua Zhao
While the type-I seesaw model provides an attractive framework for simultaneously explaining the origin of
neutrino masses and the
baryon asymmetry of the Universe,
flavor symmetries offer a natural approach to understanding the observed
neutrino mixing pattern. However, the highly constrained
neutrino mass structures predicted by
flavor symmetries may also prevent conventional leptogenesis to work. In particular, when the Dirac
neutrino mass
matrix $M^{}_{\rm D}$ or the Majorana right-handed-
neutrino (RHN) mass
matrix $M^{}_{\rm R}$ is exactly degenerate (namely, they are proportional to the identity
matrix $I$), the CP asymmetry of RHN decays will vanish either due to the orthogonality of different
neutrino Yukawa coupling columns or the exact degeneracy of RHN masses. In this work, we propose that the flavon fields (which are inherently present in
flavor-
symmetry neutrino mass models to be responsible for generating the nontrivial
neutrino flavor structure) can naturally overcome these obstacles. For the case of $M^{}_{\rm D} \propto I$, flavon–RHN interactions induce additional decay channels $N_I \to N_J \phi$ and generate new CP-violating contributions to RHN decays. For the case of $M^{}_{\rm R} \propto I$, three-body decays $N_I\rightarrow L^{}_\alpha H\phi$ mediated by heavy vectorlike
fermions provide a CP asymmetry source even when the RHN masses are exactly degenerate. Our results demonstrate that the flavon sector provides a natural connection between
neutrino flavor structure and leptogenesis, offering a new mechanism for leptogenesis in
flavor-
symmetry-based
neutrino mass models.
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Atomic Physics
Raman Transitions in Collinear Laser Spectroscopy for High-Precision Frequency Measurements
Julien Spahn, Hendrik Bodnar, Kristian König et al. (+2 more)
We demonstrate stimulated Raman spectroscopy on dipole-forbidden fine-structure transitions in a fast ion beam. It is applied to the $\mathrm{S}_{1/2}\rightarrow\mathrm{D}_{5/2}$ clock transition in $^{88}\mathrm{Sr}^{+}$ and combined with a subsequent E1 transition to allow for its detection by standard fluorescence detection. Building on this, the $\mathrm{D}_{3/2}\rightarrow\mathrm{D}_{5/2}$ fine-structure splitting is measured directly using a Doppler-free scheme employing two subsequent Raman transitions. These measurements demonstrate a path toward precision collinear
laser spectroscopy of narrow transitions on short-lived isotopes beyond the linewidth limit of conventional electric-dipole spectroscopy, which can be used to probe fundamental aspects of atomic and
nuclear physics.
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All authors Julien Spahn, Hendrik Bodnar, Kristian König, Wilfried Nörtershäuser, Robbe Van Duyse
Atomic Physics
Reconstructing Molecular-Ion Quantum States with Two-Color Strong-Field Scattering
Dina S. Eissa, Felipe Morales, Abraham Camacho Garibay et al. (+6 more)
Strong-field ionization of molecules can prepare coherent superpositions of ionic states whose amplitudes and relative phases govern the ensuing ultrafast dynamics, but accessing this information experimentally remains a challenge. Here we introduce two-color strong-field scattering, in which a strong mid-infrared field ionizes the molecule and launches an electron, while a weak second harmonic field resonantly couples vibronic states of the parent ion during the electron's continuum excursion, thereby introducing structural changes on the sub-
laser-cycle timescale. Scanning the relative phase between the two colors controls the ionic
evolution and maps it onto phase-dependent sub-angstrom bond-length changes retrieved from the rescattering signal. Using the example of N$_2$, we apply the two-color setup to probe the coherence between different ionization channels and to reconstruct the initial ionic superposition. Our results establish two-color strong-field scattering as a powerful structural approach to characterize the complex amplitudes of ion
quantum wavepackets.
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All authors Dina S. Eissa, Felipe Morales, Abraham Camacho Garibay, Vyacheslav Leshchenko, Cosmin I. Blaga, Misha Ivanov, Pierre Agostini, Maria Richter, Louis F. DiMauro
Quantum Physics
Circuit-level benchmarks of GKP-concatenated qLDPC Codes
Yuan Yao, Ruipeng Xing, Jianshuo Gao et al. (+1 more)
Scalable fault-tolerant
quantum error correction based on Gottesman-Kitaev-Preskill (GKP) codes requires finite-rate outer codes that can exploit analog GKP information under realistic
circuit noise. However,
quantum low-density parity-check (qLDPC) outer codes have not been systematically compared as candidates for
circuit-level GKP concatenation. Here, we
benchmark BB and tricycle codes using a unified simulation framework that progresses from code-capacity noise to repeated noisy syndrome extraction and schedule-resolved displacement propagation. Across all three noise models, analog-informed belief-propagation with ordered-statistics decoding (BP-OSD) yields higher finite-size crossing estimates than hard-decision decoding. In the full
circuit model, the analog-informed crossings are \(\sigma_{\mathrm{th}}\simeq0.212\) for the selected BB sequence and \(0.142\) for the tricycle sequence, corresponding to squeezing requirements of approximately \(10.46\,\mathrm{dB}\) and \(13.94\,\mathrm{dB}\), respectively. These results show that analog GKP information continues to improve decoding under
circuit-level noise. Under the common simulation assumptions used here, the selected BB sequence also yields a higher finite-size crossing estimate than the selected tricycle sequence.
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All authors Yuan Yao, Ruipeng Xing, Jianshuo Gao, Xiao Yuan
Medical Physics
Physics-informed self-supervised generation of digital brain MRI phantoms from weighted images using differentiable MRI simulation
Kseniya Belousova, Anna Konanykhina, Zilya Murzina et al. (+2 more)
Purpose: To develop a physics-informed, self-supervised framework for generating digital
brain MRI phantoms directly from conventional weighted MR images without requiring ground-truth parametric maps or anatomical
segmentation. Methods: The framework predicts T1, T2, and
proton density (PD) maps from T1-, T2-, and PD-weighted images and reconstructs the input images through an MRI signal model. Three generative architectures (variational autoencoder (VAE), generative
adversarial network (GAN), and flow-based model) were compared. Models were pretrained on 3,739 synthetic
brain slices generated using digital phantoms and an analytical MRI signal model, followed by fine-tuning on 90 real
brain slices from three healthy volunteers. The best-performing architecture was subsequently fine-tuned using the differentiable MR-Zero numerical MRI simulator and evaluated on 30 held-out real slices. Results: The flow-based model demonstrated the highest overall performance and preserved fine anatomical details better than the VAE and GAN. After analytical-model fine-tuning, it achieved MS-SSIM values of 0.955-0.985 and PSNR values of 26.68-32.63 dB across T1-, T2-, and PD-weighted images. Fine-tuning with MR-Zero increased T1-weighted reconstruction quality from 0.955 to 0.977 (MS-SSIM) and from 26.68 to 30.60 dB (PSNR), and provided high robustness of metrics across different MR image weightings. The resulting digital phantoms also enabled simulation of images using previously unseen acquisition protocols. Conclusion: The proposed framework enables physics-informed generation of reusable digital
brain MRI phantoms from weighted images using limited real-world data. Combining synthetic pretraining with differentiable numerical MRI simulation provides a practical approach for physically grounded MRI data augmentation without requiring reference parametric maps.
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All authors Kseniya Belousova, Anna Konanykhina, Zilya Murzina, Walid Al-Haidri, Ekaterina Brui
Quantum Physics
Generalized LIMDDs: Succinctness and Canonicity for Decision Diagrams Modulo a Group
Arend-Jan Quist, Alexis de Colnet, Thomas Reps et al. (+1 more)
A reduced ordered decision diagram is the minimal automaton of a function on words of fixed length: its nodes are the residuals, and reduction is the Myhill–Nerode quotient. We study what happens when that quotient is coarsened by a group. Fix a group $G$ acting on residuals, merge two nodes when their residuals lie in one $G$-orbit, and record the group element on the edge. For functions $\{0,1\}^n\to\mathbb{C}$ and $G$ the Pauli group this is the Local Invertible Map Decision Diagram. We take $G$ from the two-parameter family generated by $C^{\leq k}R_q$, the phase rotation of order $q$ with up to $k$ control
qubits, with and without the bit flip $X$. We show that this gives exponential succinctness improvements compared to Pauli-LIMDD, and we determine the succinctness order of the family completely. The separating objects are hypergraph states, which can always be efficiently represented by some member of the family. We settle the tractability of five queries and eight transformations, which is invariant across the family, and shows the same behavior as Pauli-LIMDD. We give a five-rule reduction system whose normal forms are unique for every member of the family, and we show that this canonical form is computable in
polynomial time in the size of the LIMDD. We show that, when coarsening beyond the (anti-)diagonal groups, the calculation of a minimal sized normal form turns out to be non-local and it might to rebuild the whole diagram.
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All authors Arend-Jan Quist, Alexis de Colnet, Thomas Reps, Alfons Laarman
Disordered Systems and Neural Networks
Attraction-controlled torque organization and rotational states in frictional granular matter
Kiwamu Yoshii
In this study, we numerically investigate how interparticle attraction affects stress transmission, torque organization, and particle rotation in a two-dimensional frictional granular material. Although the attraction is a central force and exerts no direct torque on the particles, it strongly modifies the contact network and particle rotation. Attraction produces a low-rate stress state and selects the high-stress state near the shear-thickening regime of the dry system, while leaving the high-rate thickened state almost unchanged. By decomposing the shear stress, we find that the direct attractive contribution accounts for only a fraction of the total stress, while the repulsive contribution is strongly enhanced. Attraction increases the coordination number and torque amplitude and can reverse the local torque-sign correlation. At low packing fractions and intermediate shear rates, a stress-collapse state emerges with strongly suppressed torque and rotation despite a finite contact network. These results show that attraction controls macroscopic rheology through reorganization of the frictional contact network.
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Quantum Physics
Gauge freedom and efficient algorithms for Lindbladian learning
Steven T Flammia, Savar D Sinha and Yu Tong
We study the problem of learning a local Lindbladian in the presence of state-preparation-and-measurement (SPAM) noise. Although recent work has developed scalable learning
algorithms under idealized access assumptions, SPAM can make distinct Lindbladians experimentally indistinguishable, thus making part of the Lindbladian fundamentally unlearnable. We give a sharp characterization of this obstruction for bounded-degree local Lindbladians. We identify a family of locality-preserving gauge transformations that commutes with trusted single-
qubit control, and use it to classify Lindbladian components. For the generically gauge dependent components, we construct Lindbladians to show that they can have $\Omega(1)$ uncertainty independent of system size, even after imposing complete positivity. We complement this characterization with SPAM-robust
algorithms for learning every universally gauge-invariant component. Our
algorithms use only trusted single-
qubit operations, require neither ancillas nor entangling control, and use $\widetilde{\mathcal O}\left(\epsilon^{-2}\log(N/\delta)\right)$ experiments and total
evolution time for constant locality and degree. Our guarantees allow global SPAM to become arbitrarily far from ideal as $N$ grows, requiring only nonvanishing local visibility. We also establish sufficient conditions for boundary-induced gauge invariance of additional
Hamiltonian coefficients under physical positivity constraints, though learning these additional parameters in general remains an open problem. More broadly, our gauge-aware framework and SPAM-cancellation techniques offer a practical toolkit for the scalable characterization of open
quantum systems.
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Fluid Dynamics
A Conservative Multi-Level Adaptive Velocity-Space Method for the Discrete Unified Gas-Kinetic Scheme
Weijie Ren, Hang Yu, Zhengyu Tian et al. (+2 more)
Multiscale gas flows often span a wide range of Knudsen numbers, within which the flow varies from near-continuum to highly rarefied and strongly nonequilibrium states. Such flows require kinetic solvers that remain accurate across the entire range. The discrete unified gas-kinetic scheme (DUGKS) provides such a unified description, but its computational cost and
memory consumption are dominated by the size of the discrete velocity space. To alleviate this bottleneck, this work improves the DUGKS with multi-level adaptive velocity-space discretization (MLVS-DUGKS), reducing velocity-space redundancy while preserving accuracy and conservation. This method identify the velocity-space requirements of each physical
cell from its distribution function, and then groups these requirements into a small number of representative velocity spaces. This organization retains sensitivity to different local flow states without constructing an independent velocity space for every physical
cell. A linear moment-constrained correction is incorporated to maintain discrete compatibility and conservative data transfer between representative velocity spaces.
Benchmark simulations spanning near-continuum to highly rarefied regimes show close agreement with the uniform-velocity-space DUGKS (UVS-DUGKS). For the computationally demanding cases, the average number of discrete velocity points is reduced by approximately one order of magnitude, yielding speedups of 6.67–7.51 and GPU-
memory reductions by factors of 6.15–6.88. A threshold study further shows that the actual computational performance is governed by a balance between velocity-space compression and cross-level coupling overhead. The MLVS-DUGKS thus provides an accurate, conservative, and computationally efficient framework for multiscale nonequilibrium-flow simulations.
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All authors Weijie Ren, Hang Yu, Zhengyu Tian, Wenjia Xie, XiaoQiang Fan
High Energy Physics (Theory)
Exotic gravity theory in topologically non-trivial spacetimes
P.S. Howe and U. Lindström
An exotic linearised theory of superconformal
gravity in $D=6, (4,0)$ superspace has been proposed by C.M. Hull. In this note we discuss the bosonic sector of this model in topologically non-trivial spaces. Roughly speaking, Hull's model can be thought of as a square of the $H=dB$ theory, although not all Hull fields can be so presented. We also briefly discuss the form sector of $D=11$ supergravity.
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Quantum Physics
An Exact Polynomial Task-Risk Bridge for Time-Multiplexed Photonic Quantum Reservoirs
Yuqi Zhang, Tianyu Zhou, Yilun Jiang et al. (+2 more)
Time-multiplexed (TDM) photonic reservoirs are usually judged by their scores on a few
datasets, which say little about a chip's overall performance, and designed by enumerating candidate
circuits and simulating each one, which is inefficient and gives no guarantee of finding a good structure. For a time-unrolled passive linear network with data-modulated gates or sources and a ridge readout, we derive an exact bridge from the task to the prediction risk in three steps. (i) Task features: the finite-shot risk depends on the time series only through finitely many statistics of its training windows and their correlations with the target, selected by the encoding and the optical paths. (ii) Encoding: every output moment is a
polynomial in the features of the data-modulated sites, with degree and support bounded by tuples of optical paths. Gate encoding reads the characteristic function and creates interactions across time lags; squeezing encoding reads the moment-generating function and displacement encoding low-order moments, and with quadrature receivers they yield only additive and linear models, respectively, for every
topology. (iii) Readout: for homodyne, heterodyne and
photon-number receivers the risk closes exactly, and its dependence on the number of shots is an explicit sum over signal-to-noise modes; threshold clicks admit finite-dictionary approximations with certified error. Parts of the network that share no light carry independent states, which a receiver combines only through measurement events that join them. Checks on seven
datasets confirm every exact statement to machine precision. The three steps thus yield a useful space of candidate TDM architectures, pruned by exact statements rather than by trial simulation, which can in future guide the selection of TDM chips for target requirements.
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All authors Yuqi Zhang, Tianyu Zhou, Yilun Jiang, Tian Chen, Hao Tang
Quantum Physics
Computational Complexity of Clifford Template Compilation: Are Quantum Computers Useful for Compiling Quantum Circuits?
Keisuke Fujii
A Clifford template is a finite ordered family of repeatable Clifford operations, and an instantiation specifies how many times each operation is applied. The Clifford template compilation problem asks how to choose these repetition numbers so that the template realizes a target transformation of Pauli operators. This problem arises, for example, when searching for logical operations in
quantum error correction using only Clifford operations permitted by physical or fault-tolerance constraints. Although forward Clifford dynamics is efficiently classically simulable, this inverse problem has sharp complexity transitions. For commuting templates with unrestricted integer exponents, feasibility lies in $\mathrm{NP}\cap\mathrm{BQP}$ and a constructive
quantum algorithm returns a particular solution together with the full exponent-relation
lattice; already at $k=1$, recovering the repetition number contains finite-field discrete logarithm over $\mathbb{F}_{2^r}^{\times}$. In general, restricting every exponent to $\{0,1\}$ removes the Abelian-group closure and makes feasibility NP-complete for variable $k$, even for exactly commuting CNOT-only operations and X-type Paulis. For commuting self-inverse Clifford actions, both binary feasibility and recovery of one solution are classically
polynomial-time solvable, but imposing a bound on the total repetition count is NP-complete, even for CNOT-only operations. These results reveal a rich complexity landscape within Clifford template compilation, spanning classically tractable cases, problems admitting
quantum polynomial-time
algorithms, and NP-complete variants.
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Quantum Physics
A technological capability scale for civilizations from the Kardashev and Barrow scales
Volkan Gurses
We introduce a technological capability scale that ranks civilizations by the control operations they can perform per second. A control operation is defined as setting one binary degree of freedom of matter to a specified value, whatever its previous state. Building on constructor theory, we sort them into construction and its special cases on information media, namely processing, storage and transfer. The index $\Xi = K + B$ adds to the Kardashev index $K$ an efficiency index $B$ of energy per operation, measured from the thermal floor at the microwave background temperature. The Kardashev scale gives the ceiling for resets of thermally random bits with heat radiated into the present sky, and the Barrow scale gives the floor, which for such a reset is the thermal floor at the heat-rejection temperature at every level. Since 1950 the energy per logic operation has fallen 11.7 orders of magnitude, around 5 through miniaturization. Humanity, at $K = 0.73$, computes with CMOS logic gates at $B = -0.78$ in primary energy. We describe the ultimate technology, at $\Xi = 7.58$, which would dissipate the conjectured largest power $c^5/4G$ into an uncharged, non-rotating black hole near its largest mass in de Sitter space.
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Disordered Systems and Neural Networks
Exact probability distributions of complex spacing ratios in non-Hermitian random matrices
Kohei Kawabata
The complex spacing ratio is the complex displacement from a reference
eigenvalue to its nearest neighbor divided by the corresponding displacement to its next-to-nearest neighbor. Its statistics provide a useful diagnostic of spectral correlations and nonintegrability in open
quantum systems. Here, starting from the exact joint
eigenvalue probability densities, we derive finite-$N$ complex-spacing-ratio distributions for the Gaussian ensembles of non-Hermitian random
matrices in classes AI$^{\dag}$ and AII$^{\dag}$, realized by complex symmetric and complex self-dual random
matrices, respectively. In class AII$^{\dag}$, we obtain an exact algebraic expression for arbitrary $N$ and explicitly evaluate the distributions and representative moments for $N=3, 4, 5, 6$. In class AI$^{\dag}$, although the joint density retains a noncompact integral over nonunitary eigenvector degrees of freedom, we analytically derive a normalized one-dimensional integral representation for $N=3$ and determine the asymptotic behavior, including a logarithmic correction to the cubic level repulsion and a nonanalytic contribution to the angular density. We further confirm these analytical results through direct numerical diagonalization of non-Hermitian random
matrices.
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General Relativity and Quantum Cosmology
A Cuscuton Representation of the Loop Quantum Cosmology Bounce
Niayesh Afshordi and Kristina Giesel
Loop
Quantum Cosmology (LQC) replaces the big bang singularity of the homogeneous universe by a bounce, usually described by the modified Friedmann equation $H^2=\rho(1-\rho/\rho_c)/(3M_p^2)$. We show that this background dynamics follows from a local cuscuton effective theory, whose scalar equation is a constraint rather than a wave equation. One way to establish this is to write the cuscuton in terms of an angular coordinate $\theta$, identified with the LQC polymerization angle $2\lambda b$. Its constraint gives $H\propto\sin\theta$, while the Einstein constraint gives $\rho=\rho_c\sin^2(\theta/2)$, exactly reproducing the LQC bounce. To our knowledge, this is the first closed-form, local, generally covariant realization of the exact standard flat-FLRW LQC background dynamics for minimally coupled matter satisfying null energy condition, without introducing additional local dynamical degrees of freedom. A branchwise Legendre transformation establishes a canonical equivalence between the clock-gauge-fixed homogeneous mimetic system in the case of vanishing mimetic
dust energy density and the cuscuton systems. It selects the constant-tension cuscuton coordinate $\Theta=\sin\theta-\theta$, while $\theta$ retains its interpretation as the LQC polymerization angle. This equivalence does not establish agreement of the inhomogeneous theories or their perturbations. The angular action also admits an explicit branched $f(K)$ representation, where $K$ is the mean extrinsic
curvature of spatial hypersurfaces. The construction is therefore an effective covariant representation of the LQC holonomy correction, not a derivation from full loop
quantum gravity.
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