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Physics

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Monday 7 September

High Energy Astrophysical Phenomena

A cosmic-ray database update: CRDB v4.2

Davud Maurin

The cosmic-ray database, CRDB, has provided data and meta-data to the community since 2013. We present a new release, CRDB v4.2, which includes data and time series published in the last three years (from AMS-02, CALET, DAMPE, LHAASO, etc.), datasets missed in previous releases, and all peer-reviewed ultra-high energy cosmic-ray data (both historical and recent datasets). These data and meta-data are available from the web interface or from the CRDB pip-installable Python library. This release includes results from more than 60 experiments and publications, corresponding to 4534 new data points and 131624 time-series data points.
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Mathematical Physics · Cross-listed from math.PR

On the stationary measures of the critical Ornstein–Uhlenbeck process

Jean-Dominique Deuschel, Jonas Köppl, Yannic Steenbeck et al. (+1 more)

We study linear and symmetric diffusion processes on $\mathbb{R}^{\mathbb{Z}^d}$ that can be seen as the Langevin dynamics of the (inhomogeneous) harmonic crystal for given conductances, with a particular focus on their stationary distributions. Despite the linearity of the interaction, we exhibit a rich variety of behaviours, depending on the disorder encoded by the conductances. Our main results provide essentially sharp criteria on the conductances ensuring that every stationary measure is reversible. We also provide examples for which these criteria fail and where either no stationary measures exist or reversible and non-reversible stationary measures coexist. Additionally, we show that the linear system can even exhibit non-trivial time-periodic behaviour and provide a spectral characterisation of the occurrence of such oscillations. The case of deterministic conductances is complemented by a study of the case of random conductances under quite general moment assumptions.
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All authors Jean-Dominique Deuschel, Jonas Köppl, Yannic Steenbeck, Thomas Worschech

Statistical Mechanics

Microcanonical Hamiltonian Monte Carlo and the Helmholtz Theorem

Heinrich von Campe and Bjoern Malte Schaefer

The recently proposed Microcanonical Hamiltonian Monte Carlo algorithm has not yet been studied in detail from a thermodynamic point of view; this work aims to fill that gap. We demonstrate how thermodynamical state variables and potentials can be derived and thereby demonstrate that the construction of the algorithm formally represents a microcanonical thermodynamic ensemble. In particular, we demonstrate (analytically and numerically) that the algorithm fulfils the Helmholtz theorem, an alternative formulation of the first law of thermodynamics. Furthermore, we construct a new sampling algorithm that extends the original to lower-dimensional inference problems. Finally, we argue that canonical Markov Chain Monte Carlo algorithms are more natural than Microcanonical Hamiltonian Monte Carlo from the thermodynamic and information-theoretic point of view.
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Other Condensed Matter

Topological Edge States and Collective Radiation in a One-Dimensional Atomic Chain

Arda Deniz İyican, Ahmet Levent Subaş{\i} and Özgür Çak{\i}r

We investigate the topological and collective radiative properties of a one-dimensional diatomic chain of identical quantum emitters with alternating spacing, coupled to the electromagnetic vacuum. The system realizes an extended, non-Hermitian Su-Schrieffer-Heeger-type model with vacuum-mediated long-range interactions and collective dissipation. We focus on the single-excitation manifold, where the dynamics are described by an effective Hamiltonian. For an infinite chain, the complex band structure reveals subradiant modes associated with wave vectors outside the light line, as well as parameter regimes where real-part band crossings occur. The bulk topology is characterized by a complex Berry phase, which remains quantized in the presence of inversion symmetry and a spectral gap. For finite chains, using exact diagonalization, we identify superradiant, subradiant, and edge states with distinct decay rates and spatial profiles. Edge states emerge in the topologically nontrivial regime when a bulk gap in the real part of the energy spectrum is present, while subradiant states exhibit strongly suppressed decay with system-size dependence. Finally, we analyze the far-field radiation patterns associated with different classes of eigenstates and show that the emission characteristics reflect the decay properties, spatial localization, and the parity of the unit-cell amplitudes.
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Quantum Physics

Experimental realization of quantum-computing-enhanced sensing

Yifang Xu, Hongwei Huang, Yilong Zhou et al. (+14 more)

Quantum algorithms offer computational advantages, yet incorporating them into quantum sensing and converting these advantages into enhanced information acquisition remains challenging. Here, we realize quantum-computing-enhanced sensing in a spin-oscillator architecture, where a microwave cavity provides a high-dimensional quantum register and a coupled superconducting qubit serves as the sensor. The unknown signal directly generates the phase oracle operation, establishing a natural physical interface between quantum computation and sensing. We experimentally demonstrate the first Grover search in a bosonic mode and observe quantum amplitude amplification in a Hilbert space spanning more than 128 photons. For the same number of sensing iterations, our protocol extracts more information and resolves more frequency candidates than classical sequential search. Our results establish signal-driven oracles as a route for harnessing oracle-based quantum algorithms and realizing quantum-computing-enhanced sensing.
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All authors Yifang Xu, Hongwei Huang, Yilong Zhou, Yunlai Zhu, Chuanlong Ma, Lida Sun, Lintao Xiao, Ziyue Hua, Weiting Wang, Zijie Chen, Weizhou Cai, Hekang Li, Haohua Wang, Xiaoting Wang, Ming Li, Chang-Ling Zou, Luyan Sun

High Energy Physics (Theory)

Exact spin form factors and correlations at a massive Kramers-Wannier interface

Zoltan Bajnok and Yizhuang Liu

We determine exact finite-volume spin form factors and two-point correlations for a massive Kramer–Wannier interface in the scaling Ising model, separating ordered and disordered phases. The interface admits two complementary lattice realizations: a self-dual inhomogeneous Ising chain whose continuum limit has a sign-changing Majorana mass profile, and, after exchanging Euclidean space and time, a mixed thermal average amenable to Toeplitz/Fredholm methods. Combining these descriptions, we obtain the exact Neveu-Schwarz-Ramond spin matrix elements and a factorized Fredholm determinant for the interface correlator. Defect TCSA and independent fermionic spin-chain calculations confirm the predicted spectrum and matrix elements.
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Quantum Physics

Quantum Approximate Counting with Bernoulli Oracles

Chengshen Gao, Yongzhen Xu and Lvzhou Li

Quantum counting is a fundamental quantum algorithm that estimates the fraction of marked elements using a membership oracle, achieving a quadratic speedup over classical sampling. The membership oracle, however, assumes exact labeling of each element, but this assumption fails when the labels are inherently probabilistic. We study quantum counting with Bernoulli oracles, where given $m$ Bernoulli distributions with unknown biases $p_1,\dots,p_m$ and a gap parameter $\Delta$, the goal is to estimate the fraction $\rho$ of positive distributions ($p_i\ge1/2+\Delta$) to within additive error $\epsilon$. We prove an upper bound of $\tilde{O}\!\big(\frac{\sqrt{\rho}}{\Delta\epsilon}+\frac{1}{\Delta\sqrt{\epsilon}}\big)$ queries, achieving a quadratic speedup over the classical sample complexity. % of $\Theta(\rho/\Delta^2\epsilon^2)$. Our algorithm first uses the Quantum Singular Value Transformation (QSVT) to coherently amplify the bias gap without collapsing the superposition over distributions, and then applies two-stage adaptive amplitude estimation. We complement this upper bound with a near-matching lower bound of $\Omega(\sqrt{\rho}/(\Delta\epsilon))$ via a new composition theorem for the quantum adversary method in the Boolean-over-average-case direction. For the special case of a constant gap $\Delta=\Theta(1)$, which corresponds to the bounded-error oracle where each query returns the correct label with constant probability, our bounds specialize to $\tilde{O}\big(\frac{\sqrt{\rho}}{\epsilon}+\frac{1}{\sqrt{\epsilon}}\big)$ and $\Omega(\frac{\sqrt{\rho}}{\epsilon})$, thereby characterizing the query complexity of quantum counting with bounded-error oracles.
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General Relativity and Quantum Cosmology

Global structure and stability of Kerr-Bertotti-Robinson spacetime

Yu-Sen Zhou, Liang-Bi Wu, Ming-Fei Ji et al. (+3 more)

The surface $r=\infty$ of the Kerr-Bertotti-Robinson spacetime is not a genuine boundary. We construct its natural analytic extension and show that $r=+\infty$ of one KBR region is smoothly connected to $r=-\infty$ of a neighboring one. Repeated continuation produces an infinite chain of regions connected by wormhole-like bridges and exposes the neighboring ring singularity without an intervening horizon, which violates the weak cosmic censorship conjecture. We then study a test massless scalar field on a two-universe scattering segment to probe the stability of the spacetime. For axisymmetric perturbations, we analytically establish purely imaginary growing quasinormal modes for every $\ell$ and trace their origin to the chronology-violating region. In the $(\ell,m)=(2,2)$ sector, unstable branches occur for sufficiently large rotation and sufficiently small magnetic field. Their marginal real modes obey an exact horizon-flux balance, supporting a black-hole-bomb interpretation in which superradiant extraction is amplified by trapping within the double-barrier potential. The same cavity also supports families of weakly damped modes and may produce echo-like responses.
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All authors Yu-Sen Zhou, Liang-Bi Wu, Ming-Fei Ji, Wen-Tao Fu, Li-Ming Cao, Rong-Gen Cai

Quantum Physics

Topology Obstructs Pure Foundation Neural Quantum States

Timothy Heightman, Elena Orlova, Philip Mantrov et al. (+1 more)

Foundation models for ground states in spin-1/2 systems are a promising method for problems ranging from quantum chemistry to identifying new phase diagrams. Nearly all such models are currently pure-states that condition on the Hamiltonian's parameters, whose Monte Carlo samples give energy estimates according to the variational principle. In this contribution, we show that this representation is topologically obstructed. For any gapped Hamiltonian family whose ground-state bundle is non-trivial, every continuous normalized state-vector model has zero fidelity with the ground state at some parameter value in the Hamiltonian family. For that value, the energy is at least one spectral gap, $\Delta$, with an $O(\Delta)$ gap in an open-neighbourhood of that point. We show that this is a sufficient no-go also in the case of degenerate ground-state manifolds, time dynamics, and periodic systems with mixed space-time topology, demonstrating these obstructions on one- and two-qubit systems. We discuss how this causes a spike in the fidelity susceptibility, giving a numerical signature of a phase-transition where there is none. We then show that operator-valued models canonically avoid these obstructions and preserve topological information, implying a structural necessity in representation for foundation neural quantum states.
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All authors Timothy Heightman, Elena Orlova, Philip Mantrov, Aleksei Ustimenko

Mesoscale and Nanoscale Physics

Encapsulated macroscopic WS$_2$ monolayers enable room-temperature exciton-polariton lattices

Shiyu Huang, Sander Scheel, Jiang Qu et al. (+11 more)

Large-area, optically homogeneous monolayer semiconductors are a critical prerequisite for scalable room-temperature polaritonics and for realizing polariton lattices extending across many unit cells. Yet, the small size, optical inhomogeneity, and device-to-device variability of conventional exfoliated flakes have remained major obstacles. Here, we overcome these limitations using 1-dodecanol-encapsulated WS$_2$ monolayers that combine millimeter-scale coverage with remarkably uniform optical properties over lateral distances approaching $300\,$$\mu \mathrm{m}$. Integrated into a tunable open microcavity, these monolayers exhibit robust room-temperature exciton-photon strong coupling, evidenced by a pronounced anti-crossing and a Rabi splitting of $\hbar \Omega_{\mathrm{R}} \approx 31\,\mathrm{meV}$. Leveraging the exceptional uniformity of this platform, we realize a two-dimensional polaritonic kagome lattice and directly resolve its characteristic band structure. Angle-resolved spectroscopy reveals Dirac dispersive bands together with a weakly dispersive flat-band-like branch within the $s$-band, in good agreement with a linear non-interacting model. Complementary momentum- and real-space imaging further identifies the associated bond-centered and site-centered mode profiles. These results establish large-area WS$_2$ monolayers in open microcavities as a scalable platform for engineering polariton band structures and exploring synthetic quantum materials under ambient conditions.
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All authors Shiyu Huang, Sander Scheel, Jiang Qu, Johannes Düreth, Dominik Horneber, Edith Wietek, Simon Widmann, Libo Ma, Monika Emmerling, Martin Kamp, Simon Betzold, Alexey Chernikov, Sven Höfling, Sebastian Klembt

Plasma Physics

Self-organized positron reorienting and pinching mechanism for the experimental detection of the linear Breit-Wheeler process

Yutong He, Alexey Arefiev, Mario Manuel et al. (+2 more)

The linear Breit-Wheeler (LBW) process ($\gamma+\gamma\rightarrow e^{-}+e^{+}$) is a fundamental prediction of quantum electrodynamics, but yet to be observed under laboratory conditions using real photons. In recent years, a few experimental schemes utilizing high-intense ($\sim10^{22}$W/cm$^2$) laser-plasma interactions to observe the LBW process have been proposed. However, a high level of signal-to-noise-ratio are expected in these schemes, hindering the first-ever experimental detection of the LBW process by real photons. In this paper, we present a simple experimental setup which could enhance the expected positron signals by 2-3 orders of magnitude compared to previously proposed schemes, reaching the level of $10^{6}$MeV$^{-1}$str$^{-1}$. Moreover, such high positron signal is achieve in the direction opposite to the laser propagation, where a significantly quieter background is expected compared to the previously focused direction of laser propagation. The key to achieve this result is a newly discovered self-organized positron reorienting and pinching mechanism, enabled by the in-situ strong plasma fields from the laser-plasma interaction.
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All authors Yutong He, Alexey Arefiev, Mario Manuel, Hui Chen, Christopher Ridgers

Quantum Physics

Geometry Dependence of Error Thresholds in Two-Dimensional Toric Codes

D. Lessing, A. Langheld, C. Krämer et al. (+2 more)

We investigate how the lattice geometry influences the error thresholds of two-dimensional toric codes. In the presence of bit- or phase-flip errors, the toric code maps onto the two-dimensional random-bond Ising model (RBIM). We determine the critical behaviour of the RBIM using replica-exchange Monte Carlo simulations. While previous studies have explored thresholds for general lattice geometries under suboptimal decoders such as minimum-weight perfect matching, the rapid development of near-optimal decoders makes resolving the ultimate, maximum-likelihood code capacity relevant. We compute these optimal error thresholds on the Nishimori line for the square, honeycomb, triangular, dice, and kagome lattices. Owing to lattice duality, the phase-flip threshold on a given lattice is equivalent to the bit-flip threshold on its dual. We find that the optimal thresholds of dual-lattice pairs display a characteristic duality-driven splitting around the self-dual square-lattice, mirroring the qualitative behaviour observed for suboptimal decoders. While the average coordination number has the strongest impact on the error threshold, our results demonstrate that the detailed arrangement of vertices and plaquettes also plays a significant role in determining its precise value.
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All authors D. Lessing, A. Langheld, C. Krämer, J.A. Koziol, K.P. Schmidt

Mathematical Physics

Entropic repulsion to the middle layer

Max Mihailescu and Ron Peled

We consider $\nabla\varphi$ height functions with even and convex interaction energy $W$ on the lattice $\mathbb{Z}^d$, which are restricted to take values in the set $\{-S, \ldots, S\}$ for some integer $S \ge 1$. We study the effect of entropic repulsion, which tends to push the spin values to the middle layer. We prove that the model has a unique Gibbs measure, with exponential decay of correlations, in the cases: (a) Dimension $d=2$ at all temperatures. (b) Dimensions $d\ge3$ at all temperatures, for a wide class of $W$ with non-increasing second derivative, including the family $W(x)=|x|^p$ for $p\in[1,2]$. (c) Dimensions $d\ge 3$ at both low and high temperatures, $T\in (0,\frac{W(1)d}{4(\ln d+\ln 8)})\cup(d W(2S),\infty]$, with the normalization $W(0)=0$. At low temperatures, our proof provides an alternative to Pirogov–Sinai methods. Conversely, we exhibit a class of even and convex interaction energies $W$ which, in high dimensions and suitable temperature regimes, have multiple Gibbs measures. Though uniqueness may fail, we show that the magnetization of every Gibbs measure lies in $(-\frac{1}{2},\frac{1}{2})$. This implies the delocalization of the model restricted to take values in $\{0,1,\ldots\}$ (i.e., conditioned to lie above a floor) for all dimensions, any even and convex $W$, and all temperatures. Our methods extend to additional setups: We prove that height functions taking values in the real interval $[-1,1]$ always have a unique Gibbs measure, a result previously proved only for the quadratic interaction. For height functions taking values in $\{-S+\frac{1}{2}, \ldots, S-\frac{1}{2}\}$, $S \ge1 $ integer, we prove that the magnetization of every Gibbs measure lies in $(-1,1)$. The special case $W(x)=x^2$ of our results addresses questions left open in the work of Bricmont–El Mellouki–Fröhlich (1986).
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General Relativity and Quantum Cosmology

Matter-induced global regularity in non-polynomial quasi-topological gravity with Born-Infeld electrodynamics

Hong-Lin Liu, Zhong-Wen Feng, Qing-Quan Jiang et al. (+2 more)

We construct exact static, spherically symmetric charged solutions in four-dimensional non-polynomial quasi-topological gravity coupled to Born-Infeld electrodynamics. We focus on the model $h(p)=p/(1+\ell^{2}p)$, whose vacuum branch develops a curvature singularity at a finite radius. We show that Born-Infeld nonlinearities can remove this singularity within a finite region of parameter space, yielding globally regular geometries with an asymptotically flat exterior and a finite-curvature AdS-type core. The regular sector contains both horizonless configurations and RBHs, separated by a degenerate-horizon boundary. We further identify a continuous branch of regular black holes with a triple-degenerate inner horizon and a simple outer event horizon, satisfying $\kappa_-=0$ and $\kappa_+\neq0$. These results provide a converse example to cases in which introducing charge spoils the regularity of a black hole that is regular in vacuum. In the present model, Born-Infeld electrodynamics instead removes the finite-radius singularity of a gravitational branch that is singular in vacuum and supports globally regular charged geometries, including regular black holes with nontrivial inner-horizon structure.
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All authors Hong-Lin Liu, Zhong-Wen Feng, Qing-Quan Jiang, Xia Zhou, Xue-Ling Mu

Instrumentation and Methods for Astrophysics

Optical Flashes from Beam-Driven Light Sails with the Roman, Rubin and Euclid Observatories

James Guillochon and Abraham Loeb

The primary challenge of rocket propulsion is the burden of accelerating the spacecraft's own fuel. Light sails leave the propellant at home, with the achievable speed set by the sail area, the thermal tolerance of its material, and the power of the driving array. In GL15 we showed that leakage from a microwave array driving such a sail between habitable worlds produces Jansky-level radio transients lasting tens of seconds at $100$~pc. We take that leak to optical and near-infrared, where Fresnel matching would shrink the aperture to $\sim\!20$–$100$~m at $1\,\mu{\rm m}$, but the intensity on that aperture is $2\times10^{8}\,{\rm W\,m^{-2}}$, five orders above published directed-energy loadings. Spreading $1.5$~TW at $\sim20\,{\rm kW\,m^{-2}}$ is a $\sim10$~km phased array, pushing the emitters; Lubin's $10^{3}\,{\rm W\,m^{-2}}$ loading is a $40$~km array, comfortable but more expensive. A tenth-wave delay on $40$~m tiles sized so one tile still covers the sail leaks $0.054$ of the power ($80$~GW) into a halo. The typical Galactic detection is a single $\sim30$~s peak at $m_{\rm AB}\simeq19.4$ in F146 at $8$~kpc; a pair $87$~s apart, about one in five, is the confirmation test. Roman's Galactic Bulge Time Domain Survey reaches $109$~kpc at $8\sigma$ on a faint host, so a pointed flash of that halo is visible from anywhere in the Galaxy if the beam points at us. For $10$–$40$~km optical beamers held to $\sim\lambda/10$ at $v_{\rm max}\gtrsim250\,{\rm km\,s^{-1}}$, $N_{\rm det}=1$ wants $\Gamma_{6{\rm h}}\simeq16$ and a null search limits $\Gamma_{6{\rm h}}\lesssim49$, a factor-of-three window in launch rate. The real threshold is set by PSF-coincident stellar and instrumental transients. If intensity-limited optical beamers are commonly employed in our galaxy, this activity could be revealed by Roman, Rubin and Euclid at no additional observing cost.
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Soft Condensed Matter

Aggressive Phase Separation in Dense Mixtures of Passive and Active Particles

Purnendu Pathak, Gokul Upadhyay and Subir K. Das

Using Vicsek-like self-propulsion rule, we study kinetics of liquid-liquid phase separation in mixtures of passive and active particles. For evolutions following temperature quenches of homogeneous configurations to the immiscible region of the phase diagram, we identify a remarkably strong dependence of the domain growth exponent on the choice of final state point. The singular dependence is indicative of the possibility of even an exponentially fast growth for suitable choices of system parameters. This striking observation, supported by finite-size scaling and other advanced analyses, is despite the fact that the overall mixture density is quite high that risks congestion with the prospect of slowing down particle transport. From flocking in pure biological systems to robotic swarming, these results are of much practical relevance. Theoretical pictures suitable for interpreting such high growth rates are discussed. In this regard, we discuss coarsening in the velocity field as well that describes how the density field coarsening follows the latter.
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Strongly Correlated Electrons

Raman signatures of a non-reciprocal magnetic phase transition in Ca$_2$RuO$_4$

Giacomo Jarc, Giovanni Tartaglia, Francesco Gabriele et al. (+17 more)

The magnetic behavior of Ca$_2$RuO$_4$ represents a unique puzzle due to the interplay of strong electronic correlations, magneto-elastic interactions, and large spin-orbit coupling. At low temperatures, an anomalous Mott insulating state emerges, characterized by a complex antiferromagnetic order with a collective amplitude excitation of the magnetic moment which has been discussed in analogy with the Higgs mode. We report here evidence of a magnetic first-order phase transition driven by an out-of-plane magnetic field along the crystallographic $c$-axis of Ca$_2$RuO$_4$. Raman measurements in magnetic field reveal the emergence of mode of magnetic origin and a concomitant modification of the coupling between a phonon and the Higgs amplitude mode. Both the Raman features are characterized by a non-reciprocal hysteresis in magnetic field. Surprisingly, the observed phase transition does not affect the Raman scattering from the in-plane magnons, indicating that the dipolar antiferromagnetic order is preserved. This is consistent with the onset of a new quadrupolar field-controlled state, whose fluctuations structure can trigger an hybridization between the lattice and the magnetic Higgs mode resulting in the observed Raman features.
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All authors Giacomo Jarc, Giovanni Tartaglia, Francesco Gabriele, Filomena Forte, Anita Guarino, Angela Montanaro, Enrico Maria Rigoni, Nitesh Khatiwada, Costanza Lincetto, Gabriele Bartolini, Antonio Mastropasqua, Shahla Yasmin Mathengattil, Marco Malvestuto, Muhammad Waqee Ur Rehman, Rosalba Fittipaldi, Joachim Deisenhofer, Alexander A. Tsirlin, Antonio Vecchione, Mario Cuoco, Daniele Fausti

Geophysics

SeisBench DAS: A machine learning framework for Distributed Acoustic Sensing

Jannes Münchmeyer, Han Xiao and Frederik Tilmann

Fibre optic sensing, such as distributed acoustic sensing (DAS), has become a widespread technology for geophysical studies. To process the large-scale datasets produced by DAS, several machine learning methods have been proposed. However, without standardization of data and models, these methods lack comparability and interoperability. This introduces a gap between model developers and practitioners analyzing DAS data and inhibits adoption of deep learning for DAS. To address these limitations, here we present SeisBench DAS, an extension to the SeisBench library for machine learning in seismology. SeisBench DAS defines standard formats for DAS benchmark datasets, including standardised metadata and labels, and DAS models. It builds on the xdas framework for data ingestion and virtual array handling, and on PyTorch for reading and applying the machine learning models. Importantly, SeisBench provides an engine to efficiently apply deep learning models to diverse formats of DAS data, bridging the gap between model developers and practitioners. SeisBench DAS is designed as an open and extensible framework, allowing to easily incorporate future developments in deep learning for DAS.
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Nuclear Experiment

Independent Validation of Octupole Collectivity in radium-224 through lifetime measurements of low-lying negative-parity states

D. White, D. O'Donnell, A. Avaa et al. (+30 more)

The nucleus $^{224}$Ra is a key benchmark for octupole deformation and for theoretical descriptions of enhanced Schiff moments in reflection-asymmetric nuclei. While Coulomb-excitation measurements have established strong octupole collectivity in $^{224}$Ra, theoretical models predict that its intrinsic electric-dipole moment should be strongly quenched by a cancellation between macroscopic and microscopic contributions. Direct fast-timing measurements of the low-lying $J^\pi = 1^-_1$ and $3^-_1$ states populated following the $\beta$-decay of $^{224}$Fr at TRIUMF-ISAC were performed. Using the LaBr$_3$(Ce) detectors of the GRIFFIN array, mean lifetimes of $\tau(1^-_1) = 444(6)$~ps and $\tau(3^-_1) = 460(18)$~ps were obtained. The corresponding reduced transition probabilities agree with values inferred from Coulomb excitation, but are determined with substantially improved precision. These results provide an independent validation of the electromagnetic matrix elements associated with octupole collectivity in $^{224}$Ra and confirm a strongly-quenched intrinsic dipole moment of $D_0 \simeq 0.032~e\mathrm{fm}$. The present measurements therefore provide a stringent experimental benchmark for nuclear-structure models used in the interpretation of Schiff moments and future searches for non-zero electric dipole moments.
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All authors D. White, D. O'Donnell, A. Avaa, J. R. Murias, S. Murillo Morales, R. Umashankar, V. Vedia, C. Andreoiu, D. W. Annen, A. D. Ayangeakaa, G. C. Ball, V. Bildstein, M. Bowry, I. Dillmann, E. G. Fuakye, L. P. Gaffney, A. B. Garnsworthy, P. E. Garret, E. D. Geerlof, S. Georges, A. L. Grimes, G. F. Grinyer, G. Hackman, P. M. Jones, J. Liu, B. Olaizola, S. D. Olorunfunmi, F. Rowntree, N. K. Syeda, D. Shah, P. Spagnoletti, C. E. Svensson, F. Wu

Materials Science

Switchable Altermagnetism in a Layered van der Waals Metal-Organic Framework Driven by Spin-Crossover

Diego López-Alcalá, Alberto M. Ruiz, Andrei Shumilin et al. (+1 more)

Dynamical control of altermagnetism is a key requirement for translating its unique spin-dependent functionalities into practical spintronic devices, yet effective switching mechanisms remain largely unexplored. Here, we open an unprecedented, versatile and programmable route based on spin-crossover to switch altermagnetism on demand in molecular materials. Using density functional calculations, we demonstrate an altermagnetic ground state in the layered van der Waals MOFs MnX$_2$(tdz)$_2$ (X = Cl, Br; tdz = thiadiazole), stabilized by anisotropic interlayer exchange interactions, which gives rise to a characteristic d-wave momentum-space spin splitting and an associated spin-splitter transport response. Our findings reveal that under hydrostatic pressure, a high-spin to low-spin transition reconfigures the Mn d-orbital occupation, thus modifying the magnetic exchange network, and stabilizing a different antiferromagnetic ground state whose symmetry suppresses the nonrelativistic spin splitting. Crucially, spin-crossover switches altermagnetism not by directly altering the electronic structure, but by changing the symmetry of the magnetic ground state. These results establish molecular spin-crossover altermagnets as a platform for externally reconfigurable spintronic devices.
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All authors Diego López-Alcalá, Alberto M. Ruiz, Andrei Shumilin, José J. Baldoví

Superconductivity

Interference-controlled magnetic bound states and subgap transport in a Square–octagon superconductor

Ravi Kiran

The square–octagon lattice provides a useful setting for studying magnetic adatoms because its multisublattice structure allows different adsorption geometries to probe distinct combinations of the host electronic states. We study magnetic adatoms in an $s$-wave superconducting square–octagon lattice, focusing on the interplay between adsorption geometry, narrow and flat-band states, and subgap transport. We find that the large spectral weight associated with a flat band does not necessarily imply strong impurity–host coupling. For symmetric square-hollow adsorption, destructive interference strongly suppresses the overlap with the flat-band manifold, whereas top and octagon-hollow adsorption retain substantial overlap. This selectivity is reflected in the magnetic bound states, with the square-hollow channel supporting a predominantly atomic state, while the top and octagon-hollow states are strongly hybridized with the superconducting host. The effect develops continuously as the relevant band becomes flatter and remains pronounced in a material-motivated parameter regime. In a normal–superconductor–normal geometry, these differences are also reflected in the nonlocal subgap conductance. At a representative exchange splitting, square-hollow adsorption suppresses the low-bias conductance relative to the clean device, whereas octagon-hollow adsorption enhances it, with the square-hollow response showing a much sharper dependence on exchange splitting. Our results show that the magnetic-adatom response in narrow and flat-band superconductors is governed by the available spectral weight and by the symmetry and wave-function structure of the impurity–host hybridization.
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Superconductivity

Doping-controlled topological superconducting transition in misfit layer compounds

Hugo Le Du, Robin Salvatore, Justine Cordiez et al. (+12 more)

Achieving topological superconductivity is a key goal in quantum physics, offering a path to fault-tolerant quantum computers. A central challenge in this field is to continuously drive a material through a topological quantum phase transition to directly observe the evolution from trivial to topological superconductivity. However, finding a robust platform that allows such extreme and precise tuning remains a challenge. Here, we demonstrate a doping-controlled phase transition from a conventional to a topological superconducting state in the bulk misfit layer compound (LaxPb1-xSe)1.14(NbSe2)2. We reveal a non-monotonic phase diagram characterized by two distinct superconducting regimes separated by a non-superconducting phase at a precise doping. In the highly doped regime, the superconducting phase becomes remarkably sensitive to non-magnetic disorder, and orientation-selective in-gap modes emerge at atomic step edges. Supported by Bogoliubov-de Gennes calculations, these emergent spatial signatures are consistent with a time-reversal-symmetric crystalline-topological order parameter. Our results establish misfit compounds as a platform to engineering topological superconductivity.
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All authors Hugo Le Du, Robin Salvatore, Justine Cordiez, Ludovica Zullo, Arindam Mukherjee, Daniel Schmieg, Dominik Volavka, Francois Debontridder, Marie Herve, Tomas Samuely, Shunsuke Sasaki, Florent Pawula, Etienne Janod, Laurent Cario, Tristan Cren

Fluid Dynamics

Marangoni flow induced by crystallization in saline droplets

Théophile Gaichies, Javier Martínez-Puig and Javier Rodríguez Rodríguez

In this article, we study the flow induced by crystallization of sodium chloride in sessile droplets. We measure flow velocities on the order of 1 $\mathrm{cm.s^{-1}} during crystallization, two orders of magnitude higher than those reported in previous studies. We show that this discrepancy is due to surface contaminants in earlier experiments. Numerical simulations reveal that in the clean case, the flow is driven by Marangoni stresses, whereas it is density- driven in the contaminated case. Consequently, droplet cleanliness significantly influences the flow which, in turn, determines the growth rate of crystals.
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High Energy Physics (Experiment)

Response of a nitrogen-filled spherical proportional counter to mono-energetic neutrons

T. Avgitas, M. Axiotis, Z. Balmforth et al. (+16 more)

Neutron spectroscopy is an invaluable tool for a wide range of scientific and industrial applications, however, current approaches suffer from limitations that restrict their field of applicability. A safe and inexpensive alternative approach to neutron detection and spectroscopy is the use of a nitrogen-filled spherical proportional counter that exploits the $^{14}\rm{N(n,p)}^{14}\rm{C}$ and $^{14}\rm{N(n},\alpha)^{11}\rm{B}$ reactions. The neutron spectroscopy capabilities of the detector are demonstrated using beams of mono-energetic neutrons. A nitrogen-filled spherical proportional counter, operating at a pressure of $1$ bar, is exposed to neutrons with energies from $0.75$ MeV to $2.75$ MeV at the Tandem accelerator of the National Centre for Scientific Research “Demokritos” in Athens. A linear energy response is observed, within the statistical precision of the measurements.
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All authors T. Avgitas, M. Axiotis, Z. Balmforth, P. Gadow, I. Giomataris, D. Fassouliotis, J. Fock, P. Knights, A. Lagoyannis, I. Manthos, L. Millins, K. Nikolopoulos, I. Oceano, C. Prodromou, L. Schweder, E. Taimpiri, C. Toukmenidis, A. Ziagkova, R. Ward

Quantum Physics

Discrete Dirac equation on quantum graphs: A model of a Dirac particle in a branched lattice

Mashrab Akramov, Carsten Trunk and Davron Matrasulov

We study the one-dimensional time-independent discrete Dirac equation on graphs with discrete edges. Both continuous and discrete formulations of the graphs are considered, with particular focus on star graphs with three edges as a simple example. Exact solutions for eigenstates and spectra are derived and compared with the continuum case, showing good agreement in tabulated results. This approach offers a systematic framework for analyzing relativistic quantum transport on branched structures relevant to nanostructures and quantum device design.
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Quantum Physics

Toward Fault-Tolerant Variational Optimization: QAOA under [[4,2,2]] Error Detection

Matteo Robert Child, Emanuele Dri, Giacomo Vitali et al. (+2 more)

We present a partially fault-tolerant implementation of QAOA based on the $[[4,2,2]]$ error-detection code, targeting the Max-Cut problem on a square graph. Our main contribution is a novel ancilla-mediated logical $R_{ZZ}$ gate enabling interactions between qubits in different $[[4,2,2]]$ blocks. We evaluate unencoded and encoded circuits under five noise models, with both all-to-all and grid-routed connectivity, using the Cirq and qsimcirq frameworks with parallel CPU execution. Post-selection on stabilizer measurements consistently improves the probability of sampling optimal bitstrings, with five measurements providing the strongest benefit. These results support error-detection as a practical near-term strategy for improving the quality of variational quantum algorithms.
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All authors Matteo Robert Child, Emanuele Dri, Giacomo Vitali, Chiara Vercellino, Alberto Leporati

Chemical Physics

Simulation-Supervised Foundation Models for Retention Time Prediction in High-Performance Liquid Chromatography beyond Experimental Data Coverage

Stephen Wu, Yufeng Han, Yasuhiro Mito et al. (+5 more)

Accurate prediction of high-performance liquid chromatography (HPLC) retention times (RTs) across diverse molecules and chromatographic methods remains challenging because experimental training data cover only a limited region of chemical and method spaces. Here, we develop FUSE-RT (Foundation model Unifying Simulation and Experimental supervision for Retention Time), a multitask foundation model that integrates RT data from 179 chromatographic methods and adapts to unseen molecules and methods using limited target-domain data. To extend transferability beyond experimental coverage, we introduce simulation-to-real (Sim2Real) transfer learning, in which molecular representations learned from large-scale computational data are transferred to experimental RT prediction. Specifically, we use PolyOmics, comprising 39 properties for approximately 21,400 molecules generated by molecular dynamics and density-functional theory calculations, as auxiliary supervision. We evaluate generalization under molecular, method, and joint molecular–method distribution shifts. Simulation-derived supervision substantially improves transfer beyond the experimental molecular domain, particularly under pronounced coverage gaps and few-shot adaptation. Moreover, RT-prediction error decreases systematically with increasing simulation-data size, following a significant power-law relationship. These results establish Sim2Real transfer as a scalable strategy for extending RT prediction beyond the finite coverage of experimental chromatographic data.
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All authors Stephen Wu, Yufeng Han, Yasuhiro Mito, Yoshiyuki Watabe, Yoshihiro Hayashi, Hikaru Takaya, Takuya Kubo, Ryo Yoshida

High Energy Astrophysical Phenomena

Mining the time axis with TRON - III. Discovery of a nulling pulsar towards the SMC with MeerKAT

T. Blecher, M. Geyer, O. M. Smirnov et al. (+21 more)

We report on the discovery of a nulling pulsar, PSR J0052$-$7551, in archival MeerKAT L-band observations of the Small Magellanic Cloud (SMC). The discovery was made using the image-plane transient detection pipeline, TRON, which creates a residual image for each time sample and uses a heuristic pruning strategy to identify promising candidates in the resulting temporal image cube. The TRON pipeline triggered on the approximately minute timescale variability associated with the nulling behaviour of a canonical pulsar. Follow-up MeerKAT UHF-band beamformer observations revealed a pulsar with a spin period of 0.55 s and a measured period derivative of 6.1(6)$\times$10$^{-17}$s$\cdot$s$^{-1}$. The source is seen in projection toward the periphery of the SMC, and has a dispersion measure value of 29.24(2) pc$\cdot$cm$^{-3}$, which is on the order of the expected Milky Way contribution along the line of sight. We use a Gaussian Mixture Model to fit the nulling behaviour which yielded a nulling fraction of $\sim 32$%. We find that the null lengths are consistent with an exponential distribution indicating a stochastic process. Additionally, power spectra of the UHF visibility data reveal an unexplained quasi-periodic feature at ~5$-$7 s that cannot be attributed to the source itself, RFI, or standard instrumental effects. Following on from previous image-plane detections of pulsars by the TRON approach, which relied on either scintillation or eclipsing behaviour, this is the first detection triggered by nulling. This discovery confirms TRON's sensitivity to a wide range of astrophysical phenomena of medium timescale duration.
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All authors T. Blecher, M. Geyer, O. M. Smirnov, A. Coelen, I. Heywood, I. Pelisoli, A. K. Hughes, J. S. Bright, V. Prayag, T. Myburgh, C. Tasse, B. Hugo, J. S. Kenyon, H. L. Bester, S. J. Perkins, J. Dawson, V. G. Samboco, A. J. T. Ramaila, B. Ngcebetsha, I. Sihlangu, C. Choza, V. S. Dhillon, N. Castro Segura, J. McCormac

High Energy Physics (Experiment)

Reducing simulation-related emissions in rare-event searches through optimised event biasing

P. Knights, L. J. Milligan and K. Nikolopoulos

Rare-event search experiments continue to extend their sensitivities to unprecedented levels. This requires increasingly small backgrounds, and shielding schemes that can suppress external backgrounds by several orders of magnitude. Moreover, detailed simulations are required to attain a good understanding of these experimental backgrounds. Studies have suggested, however, that simulations and computing-related tasks contribute approximately 10% to the average particle physicist's carbon footprint. With backgrounds frequently below 0.01 counts per kg of target per keV of energy, simulations require more computing resources; growing a rare-event researcher's computing-related carbon footprint. Event biasing is often applied in shielding simulations as a remedy, yet there is a lack of systematic guidance on how to maximally benefit from them. An optimisation study for the importance-splitting biasing technique is discussed, focused on balancing statistical precision with simulation CPU-time, and how this can benefit the average researcher's carbon footprint.
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Nuclear Experiment

Precision Neutron Skins of $^{208}$Pb and $^{48}$Ca from Parity-Violating Electron Scattering

PREX Collaboration: D. Adhikari, H. Albataineh, D. Androić et al. (+99 more)

We have measured the parity-violating elastic electron scattering asymmetry in the PREX and CREX experiments on ${}^{208}$Pb and ${}^{48}$Ca respectively; these are both doubly-magic nuclei whose excited states can be discriminated from the ground state by the high resolution spectrometers in Hall A at Jefferson Lab. This asymmetry provides a precise determination of the weak charge form factor at one $Q^2$ and pins down the neutron radius in these two nuclei in a relatively clean and model-independent way. This is because the $Z^0$ boson of the weak interaction couples primarily to neutrons. The heavier lead nucleus, with a neutron excess, provides an interpretation of the neutron skin thickness in terms of properties of bulk neutron matter. For the lighter ${}^{48}$Ca nucleus, which is also rich in neutrons, comparisons to microscopic nuclear theory calculations are sensitive to poorly constrained 3-neutron forces. The weak neutral form factors $F_W(Q^2)$ were extracted to be $0.368 \pm 0.013$ at $Q = 0.3977 {\rm\ fm}^{-1}$ for $^{208}$Pb from PREX-2 and $0.1304 \pm 0.0055$ at $Q = 0.8733 {\rm\ fm}^{-1}$ for $^{48}$Ca. The form factor differences $(F_{ch}-F_W)(Q^2)$ were calculated to be $0.041 \pm 0.013$ at $Q = 0.3977 {\rm fm}^{-1}$ for $^{208}$Pb from PREX-2 and $0.0277 \pm 0.0055$ at $Q = 0.8733 {\rm fm}^{-1}$ for $^{48}$Ca. Correcting for Coulomb distortions and using nuclear model information, we find the neutron skin thicknesses to be $R^{208}_{\rm skin} = 0.283 \pm 0.071$ fm combining PREX-1 and PREX-2 and $R^{48}_{\rm skin} = 0.121 \pm 0.035$ fm. This paper provides a full description of the special experimental and data analysis techniques employed for precisely measuring these small asymmetries.
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All authors PREX Collaboration: D. Adhikari, H. Albataineh, D. Androić, K.A. Aniol, D.S. Armstrong, T.D. Averett, C. Ayerbe Gayoso, S.K. Barcus, V. Bellini, R.S. Beminiwattha, J.F. Benesch, H. Bhatt, D. Bhatta Pathak, D. Bhetuwal, B. Blaikie, J.A. Boyd III, Q. Campagna, A. Camsonne, G.D. Cates, Y. Chen, C. Clarke, J.C. Cornejo, S. Covrig Dusa, M. M. Dalton, P. Datta, A. Deshpande, D. Dutta, E. Fuchey, C. Gal, D. Gaskell, M. Gericke, C. Ghosh, I. Halilovic, J.-O. Hansen, O. Hassan, F. Hauenstein, W. Henry, C.J. Horowitz, C. Jantzi, S. Jian, S. Johnston, D.C. Jones, S. Kakkar, B. Karki, S. Katugampola, C. Keppel, P.M. King, D.E. King, K.S. Kumar, T. Kutz, N. Lashley-Colthirst, G. Leverick, H. Liu, N. Liyanage, S. Malace, J. Mammei, R. Mammei, M. McCaughan, D. McNulty, D. Meekins, C. Metts, R. Michaels, M. Mihovilovic, M.M. Mondal, J. Napolitano, A. Narayan, D. Nikolaev, V.F. Owen, C. Palatchi, J. Pan, B. Pandey, S. Park, K.D. Paschke, M. Petrusky, M.L. Pitt, S. Premathilake, A.J.R. Puckett, B. Quinn, R. Radloff, S. Rahman, A. Rathnayake, B.T. Reed, P.E. Reimer, R. Richards, S. Riordan, Y.R. Roblin, S. Seeds, A. Shahinyan, P. Souder, L. Tang, M. Thiel, Y. Tian, G.M. Urciuoli, E.W. Wertz, B. Wojtsekhowski, T. Ye, A. Yoon, W. Xiong, A.J. Zec, W. Zhang, J. Zhang, X. Zheng