Quantum Physics
Optimal Scaling of Unitary Design Formation in $U(1)$-Symmetric Random Circuits: A Bottleneck Slower than Charge Transport
Toshihiro Yada
Understanding randomness formation under conservation laws is important both for characterizing chaotic phenomena in isolated
quantum systems and for
symmetry-constrained
quantum information processing. $U(1)$-symmetric random
circuits on an $N$-
qubit system provide a minimal tractable setting for this problem, in which the formation rate of
unitary designs was conjectured to be governed by charge transport in the underlying
circuit geometry. However, whether charge transport indeed sets the slowest relaxation mode has remained an open problem, due to the difficulty in deriving a tight lower bound on the symmetric design formation rate. In this work, we resolve this problem by determining the optimal scaling of the
unitary $k$-design formation rate for $k\leq O(\sqrt{\log N})$ across a wide range of
circuit geometries, including
lattices, expander graphs, and all-to-all interactions. In particular, for $k\geq 2$, we find that the formation rate is governed by a two-particle encounter rate—the rate at which two random walkers encounter each other in a given
circuit geometry. This encounter rate is parametrically smaller than the single-particle transport rate in many geometries, thereby disproving the previous
conjecture. We further establish that this encounter mechanism indeed sets the design formation rate by deriving its matching lower bound with a novel proof technique based on an auxiliary subgroup ensemble. Although this encounter mode imposes a robust bottleneck on design formation in $U(1)$-symmetric random
circuits, we also show that this bottleneck can be circumvented by using
symmetry-breaking local gates and provide an explicit protocol that achieves faster design formation. These results establish a new picture of randomness formation under conservation laws and provide guiding principles for characterizing and efficiently generating
symmetry-constrained randomness.
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Quantum Physics · Cross-listed from cs.DS
A Quantum Scaling Algorithm for Maximum-Weight Perfect Matching in General Graphs
Kourosh Mirsohi, Sandy Irani and Michael T. Goodrich
Quantum speed-ups have been obtained for many fundamental graph problems, including most variants of matching. A notable exception, however, is the maximum-weight perfect matching (MWPM) problem in general graphs with integer edge weights, which is arguably the most challenging variant of matching. We present a
quantum algorithm for MWPM in general graphs that runs in \( \widetilde{O}(n m^{2/3}\log W) \) time, where $W$ is an upper bound on the magnitude of the edge weights. This is an improvement over the best known classical combinatorial bound of \( \widetilde{O}(m\sqrt n \log W) \) in the dense regime, where $m\ge n^{3/2}$. To the best of our knowledge, this is the first
quantum algorithm to obtain an asymptotic improvement over the best classical combinatorial
algorithm for the MWPM problem in general graphs. The running time of our method accounts for QRAM initialization and access overheads up to polylogarithmic factors, as well as all classical updates to the data structures. At a high level, our
algorithm is based on a classical framework due to Duan, Pettie, and Su, but our
algorithm requires replacing certain classical tasks with
quantum methods, alternative analysis of classical procedures, and the use of alternative data structures that can be implemented effectively in the QRAM model.
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Quantum Physics
From Wavefunction Regularity to Eigenvector Conditioning: Accuracy–Cost Trade-offs of Quantum Algorithms for Non-Hermitian Transcorrelated Hamiltonians
Cheng-Lin Hong, Emiel Koridon, Paul K. Faehrmann et al. (+3 more)
The electron–electron Coulomb singularity forces cusp structure in electronic wavefunctions. This cusp structure limits wavefunction regularity and slows the convergence of expansions in smooth bases, requiring large basis sets to reach a target accuracy. The transcorrelated (TC) method incorporates this short-range behavior into the
Hamiltonian, thereby improving the regularity of the transformed wavefunction and accelerating convergence toward the complete-basis-set limit. The resulting
Hamiltonian is non-Hermitian and non-normal, which limits the direct applicability of standard
quantum algorithms. For such non-normal operators, the complexity of several recent
quantum algorithms depends explicitly on quantities related to eigenvector conditioning and
eigenvalue sensitivity. Understanding these quantities is essential for assessing both algorithmic complexity and
quantum resource requirements. In this work, we address these issues in two stages. We first study a solvable model, which provides a controlled setting for isolating how transcorrelation affects basis convergence and eigenvector conditioning. Within this setting, we investigate two distinct one-parameter Jastrow correlators. We derive the asymptotic energy-error scaling: $N^{-1/2}$ for the bare projection and $N^{-3/2}$ for both TC correlators at generic fixed parameters, with $N$denoting the basis size. Furthermore, we show that this faster convergence can yield a
polynomial improvement in the asymptotic query-complexity upper bound. We then extend the analysis to second-quantized electronic-structure
Hamiltonians and use particle-number-sector diagnostics to distinguish target-sector from auxiliary-sector conditioning. Our work provides a framework for understanding the central accuracy–cost trade-off in TC
Hamiltonians.
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All authors Cheng-Lin Hong, Emiel Koridon, Paul K. Faehrmann, Thomas D. Kühne, Stefano Polla, Werner Dobrautz
Quantum Physics
Parallel classical simulation of noisy shallow circuits: no quantum advantage in 1D
Robert Koenig and Marco Tomamichel
We consider
quantum circuits consisting of $d$ layers of nearest-neighbor two-
qubit gates acting on $n$
qubits arranged on a line, where every
qubit is independently depolarized with a constant probability before each layer. We describe a randomized parallel
algorithm which samples from the output distribution of any such
circuit to within total variation error $\delta$, with parallel runtime $2^{O(d)}\log\log(n/\delta)$ and $n 2^{O(d)}$ elementary real-arithmetic operations. Without noise, the same approach gives an exact sampler with parallel runtime $O(\log n)$. For constant depth, we further show that the input/output behavior of the noisy
quantum circuit is reproduced up to a constant error by a randomized $\mathsf{AC}^0$-
circuit, that is, a Boolean
circuit of
polynomial size and constant depth with unbounded fan-in AND and OR gates and NOT gates. Consequently, every relation problem solved by a noisy constant-depth
quantum circuit in one dimension is also solved, with essentially the same success probability, by a randomized $\mathsf{AC}^0$-
circuit. This rules out, for noisy
circuits in one dimension, the unconditional
quantum advantage established for noisy shallow
circuits in two and three dimensions, where
polynomial-size classical
circuits over the same gate set require depth $\Omega(\log n/\log\log n)$. Our
algorithm exploits the fact that depolarizing noise cuts a one-dimensional
circuit into independent pieces of logarithmic width, each of which can be sampled exactly in parallel.
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Fluid Dynamics
Two-way actuator-line coupling of a geometrically exact finite-volume beam with incompressible and free-surface flow
Amirhossein Taran, Seevani Bali, Željko Tuković et al. (+2 more)
Slender flexible structures such as mooring lines, aquaculture netting, and aquatic vegetation are too thin to be resolved economically by a body-fitted mesh, yet they exchange momentum with the flow in both directions. This paper presents a finite volume actuator-line formulation for the fluid–structure interaction of such structures, in which a geometrically exact Simo–Reissner beam, discretised by
cell-centred finite volumes, is coupled two-way to an incompressible finite volume flow solver through conservative, parallel-consistent transfer operators. The fluid velocity is sampled upstream of each beam control volume, a quasi-steady Morison-type drag closure evaluates the line force, and the equal and opposite reaction is projected into the fluid momentum equation through a normalised Gaussian kernel that conserves force. The two subsystems share a discretisation, time loop, and domain decomposition, so no external structural code is required, and the OpenFOAM implementation is released publicly. The accuracy of the drag-only closure and the conditions over which it holds are quantified against two channel
benchmarks and a wave-flume experiment, with all drag coefficients fixed in advance. In a steady confined channel flow the tip deflection of a wall-mounted cantilever falls within the range of published continuum solutions. For a flexible leaflet in sinusoidal channel flow the peak tip excursion departs from the reference at the longer forcing period. The leaflet then moves further relative to the surrounding fluid, so added-mass and history forces, which the closure omits, become important. In the wave flume the simulated stem reproduces the measured mode shape, intra-wave asymmetry, and base force, and recovers 71–83% of the oscillation range. A quasi-static reconstruction test places the remaining shortfall in omitted fluid inertia rather than in the structural model.
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All authors Amirhossein Taran, Seevani Bali, Željko Tuković, Vikram Pakrashi, Philip Cardiff
Soft Condensed Matter
Active spinners drive passive matter into chiral rotors
Dennis Schorn, Anpuj Nair S, Stijn van der Ham et al. (+2 more)
Active spinners inject angular momentum into their surroundings without persistent translation, providing a route to
chiral active matter distinct from self-propelled particles moving along curved trajectories. Recent studies have shown that spinner fluids can self-organize into rotating clusters with circulating edge currents characteristic of odd-viscous fluids. Whether angular-momentum injection alone can transmit chirality and edge-current dynamics to ordinary passive matter - and thus serve as a generic mechanism for imparting
chiral functionality to undriven material components - remains an open question. Here, we show experimentally and numerically that purely rotational
magnetic spinners can transfer chirality and edge-current dynamics to passive colloidal matter. At high passive-particle fraction, active spinners assemble into rotating clusters surrounded by passive matter. Remarkably, upon changing composition and spinner attraction, this organization turns inside out: passive colloids form rotating clusters surrounded by a
chiral spinner fluid. These passive rotors exhibit edge currents and the same angular-velocity scaling, $|\Omega|\sim R^{-2}$, as their active counterparts. A minimal model shows that spinner-mediated transverse and non-reciprocal interactions are sufficient to reproduce these complementary
chiral states and their boundary-driven dynamics. Our results establish angular-momentum injection by active spinners as a route to endow otherwise passive matter with chirality, collective rotation and boundary transport.
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All authors Dennis Schorn, Anpuj Nair S, Stijn van der Ham, Benno Liebchen, Hanumantha Rao Vutukuri
Mesoscale and Nanoscale Physics
Giant PhotoMagnetoDiode Effect
V. L. Korenev and S. A. Tarasenko
We report the observation of a photomagnetodiode effect with a
giant rectification ratio of 10 at a
magnetic field of 0.1 T. The effect consists of a diode-like dependence of the photocurrent on the applied voltage that emerges in an external
magnetic field. Such a pronounced nonreciprocity is observed in high-quality VPE-grown GaAs samples at low temperatures at interband photoexcitation. The photoconductivity is invariant upon reversing the polarity of both electric and
magnetic fields. Similar behavior with even higher asymmetry ratio is observed in photoluminescence. The findings are well described by the theory of ambipolar drift of carriers in electric and
magnetic fields together with fast surface recombination.
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Instrumentation and Methods for Astrophysics
The AI crisis for teaching: "Train your own neural network!"
Douglas Scott
Everyone seems to be thinking about so-called artificial intelligence (AI) these days. As scientists, we understand that we're not about to have a conscious computer intelligence taking over the world, but we're nevertheless concerned about how "large
language models" (LLMs) and AI "
agents" are impacting the way that we do science. This concern has generated several recent essays about the effects of AI on research, including in my own field of astronomy and astrophysics. These opinion pieces tend to miss the biggest current concern for those whose jobs combine teaching with research - although the threat to future scientific research as we know it is probably a bit concerning, the effect on teaching is an existential crisis right now! We need to hang on to the parts of education that we think are at its core - so that students coming out of degree programmes are actually able to think for themselves, "like an astrophysicist". This means emphasising to students that they should use AI tools to support their education and not to replace it. One way of explaining the importance of this principle is to point out that students should be training their own neural networks.
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Cosmology and Nongalactic Astrophysics
Exploring the Primordial Power Spectrum with Dark-Age 21 cm fluctuations
Fumiya Okamatsu, Tomo Takahashi and Shuichiro Yokoyama
We investigate the potential of future observations of the Dark Ages 21 cm power spectrum to probe the scale dependence of the
primordial power spectrum and distinguish between inflationary models. We find that the Dark Ages 21 cm power spectrum can serve as a powerful probe of inflationary physics on scales beyond the reach of current CMB observations. While models predicting nearly identical running spectral indices may remain difficult to distinguish even with future 21 cm observations, models with unconventional scale dependence can be stringently tested. We further show that combining 21 cm observations with CMB data can significantly improve the constraints, even for a moderate observational configuration. We examine the impact of the choice of pivot scale on the resulting constraints.
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Fluid Dynamics
Coupled Rigid-Body Motion and Binary Phase Change: A Sharp Level-Set/Embedded-Boundary Method
Chao-Fan Zhang, Zhong-Han Xue and Jie Zhang
We develop a sharp-interface method for freely moving solid particles undergoing pure or binary melting. A Level-Set representation preserves the particle geometry during long-distance translation and rotation, while an embedded-boundary formulation imposes hydrodynamic, thermal and solutal conditions sharply on a Eulerian Cartesian mesh.
Liquid temperature and solutal concentration are advanced with a conservative moving-cut-
cell discretization, whereas the solid temperature is transported through a geometry-consistent conservative tracer. Hydrodynamic loads, rigid-body motion and phase change are coupled iteratively within each physical time step. The method is validated progressively for rigid-body motion, prescribed-motion pure and binary melting, and fully coupled melting with free particle motion. It reproduces established reference solutions and captures wake-induced rotation of a melting sphere and the simultaneous translation, rotation and thermosolutal melting of a three-dimensional oblate ellipsoid. As a final application, simulations of a floating ice disc reveal how thermoconvective instability,
geometric confinement and melting jointly determine its spontaneous motion, with phase change feeding back on the instability through the evolving particle geometry. Additional tests establish the importance of long-time geometrical fidelity, local scalar conservation and geometry-consistent solid-temperature transport. The resulting framework provides a sharp and conservative approach for strongly coupled moving-body phase-change problems.
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High Energy Astrophysical Phenomena
Correlating Surface Magnetic Field Decay with Internal Field Depth of Isolated Neutron Stars
Kathleen Sellick and Subharthi Ray
The long-term
evolution of
neutron star crustal
magnetic fields through Ohmic decay is governed by the transport properties of the crust. In this work, we demonstrate that the depth at which the
magnetic flux is anchored plays a significant role in the dissipation timescale. We study the
evolution of the
magnetic field at the surface of the
neutron star due to the crustal field
evolution, under the assumption of Ohmic
diffusion in a curved spacetime. We employ a cumulative distribution function to parameterise the initial current distribution and explore the effects of varying the equation of state and crustal
impurity. We compare results across three
neutron star models representing varying degrees of compactness. We find that
magnetic fields anchored deeper within the inner crust experience negligible decay over timescales up to $10^{10}$ years. Significant field
evolution, necessary to explain the deficit of high-field
pulsars at advanced ages, is possible if the
magnetic currents are confined to the shallow outer crust. This result holds true regardless of the
impurity concentration or the specific
geometric thickness of the crust determined by the equation of state.
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Chemical Physics
Elasticity of polycrystalline davemaoite constrains its grain size in the lower mantle
Peiyu Zhang, Liang Yuan, Rong Huang et al. (+3 more)
Earth's lower mantle hosts large low shear-velocity provinces (LLSVPs) beneath Africa and the Pacific, but their origin remains debated. Davemaoite, a major lower-mantle mineral, has been proposed as a contributor to these anomalies; however, its experimentally measured shear modulus is approximately 30% lower than first-principles predictions, a longstanding discrepancy between theory and experiment. Here, using million-atom machine-learning molecular dynamics simulations, we show that nanoscale grain-boundary disorder, invisible to conventional x-ray diffraction, can reconcile this gap. Introducing 5.8 vol% disordered regions reduces the shear and bulk
moduli by 37% and 12%, respectively. This shear-selective softening can reproduce LLSVP-like seismic anomalies in basalt-rich assemblages, but only at disorder levels corresponding to grain sizes smaller than those expected in the lower mantle. Combining the disorder-elasticity relationship with seismic constraints, we derive a minimum davemaoite grain size of approximately 100 nm. This limit is consistent with mantle grain growth models and with attenuation-based evidence for coarse-grained LLSVPs.
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All authors Peiyu Zhang, Liang Yuan, Rong Huang, Yu Ye, Xiang Wu, Junfeng Zhang
Strongly Correlated Electrons
Weyl superconductivity from Feshbach resonance in the three-dimensional repulsive Hubbard model
Taekyoung Kim, Pit Bermes, Giorgia A. Busin et al. (+1 more)
Motivated by the first experimental realization of the
antiferromagnetic phase transition in the three-dimensional
Fermi-Hubbard model, we present a theoretical study of the model's 3D superconducting phase. By formulating a 3D extension of the Feshbach mechanism, we provide a unified microscopic picture at strong coupling in which pairing is driven by near-resonant bound states of dopants. These long-lived bound states acquire a qualitatively different internal structure in three dimensions compared to their two-dimensional counterparts, giving rise to a distinct superconducting state, namely a time-reversal
symmetry breaking $d_{x^2-y^2}+id_{z^2}$ pairing state. We also provide an estimate of the corresponding critical temperature, and provide evidence that the resulting superconducting phase hosts gapless Weyl points. Our results represent a new milestone for the field of
quantum simulation, challenging experiments and large-scale numerics alike to test our predictions.
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All authors Taekyoung Kim, Pit Bermes, Giorgia A. Busin, Fabian Grusdt
Strongly Correlated Electrons
Quantum Well Resonant Tunneling Diode Probe of Correlated States in Twisted Bilayer MoS$_2$
Chengjie Zhou, Jin-Xin Hu, Sihong Xu et al. (+4 more)
Moiré superlattices formed in transition metal dichalcogenides (TMDs) offer a versatile platform for exploring emergent
quantum phases arising from strong electronic correlations. In this work, we develop a new experimental platform, the
quantum well resonant tunneling diode (QWRTD), to probe the electronic landscape of $\approx 56.1^\circ$ twisted
bilayer MoS$_2$ (tMoS$_2$). By measuring the differential conductance ($dI/dV_{\text{Probe}}$) as a function of filling factor $\nu$ and displacement field $D$, we observe a robust integer insulating feature at $\nu = 1$ that persists across the measured displacement field range. Furthermore, we identify a displacement-field-induced fractional insulating feature near $\nu = 3/4$ for $D < -75$~mV/nm. Its temperature dependence is consistent with a generalized Wigner
crystal interpretation, although the microscopic order remains to be established. These features are also observed in another device with a similar twist angle ($\approx 56.4^\circ$). Our results provide evidence of correlated states in near-AB-stacked tMoS$_2$ and establish QWRTD as a tool for investigating strong correlations in van der Waals
heterostructures.
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All authors Chengjie Zhou, Jin-Xin Hu, Sihong Xu, Zijing Jin, Hui Li, Kam Tuen Law, Jiannong Wang
Quantum Physics
Reservoir- and Measurement-free Microwave Initialization of Semiconductor Spin Qubits
Leon C. Camenzind, Ik Kyeong Jin, Akito Noiri et al. (+4 more)
Scalable
quantum processors require repeated
qubit initialization throughout large arrays. In
semiconductor spin qubits, fast initialization commonly relies on local reservoir access or measurement-based feedback, requiring dedicated infrastructure that becomes increasingly difficult to distribute as processors scale. Here, we demonstrate reservoir- and measurement-free initialization of a silicon
spin-
qubit pair in an industrially fabricated Si/SiGe
quantum-dot device using a fixed sequence of microwave and baseband pulses. Odd
spin-parity states relax to the singlet charge state, whereas blocked even
spin-parity states are microwave-driven through the triplet
manifold and subsequently converted to the singlet by singlet-triplet mixing and charge hybridization. Repeated cycles produce the singlet-associated charge outcome with a median probability of 99.4% across the sampled preparation states, while exchange spectroscopy independently verifies mapping to the target $|\uparrow\downarrow\rangle$ operational state. Microwave spectroscopy and time-domain measurements identify the dark-state-limited single-cycle transfer and the subsequent blockade-lifting dynamics that set the initialization time scale. The demonstrated pumping sequence uses approximately $12\,\mu\mathrm{s}$ of microwave bursts and mixing dwells, while we project sub-microsecond initialization under improved device conditions. These results establish fixed-sequence microwave initialization as a scalable control primitive for
semiconductor spin-
qubit processors, based on singlet-triplet physics that can be adapted to platforms with suitable Pauli-blockade transitions.
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All authors Leon C. Camenzind, Ik Kyeong Jin, Akito Noiri, Kenta Takeda, Takashi Nakajima, Takashi Kobayashi, Seigo Tarucha
Quantum Physics
Genuine Multipartite Nonlocality Is Fermionic Magic
Jamal Slim
Free
fermion dynamics is classically simulable, and a single non-Gaussian state makes it universal. We show that the same boundary governs
quantum nonlocality. Measured as fermionic
qubits, fermionic Gaussian states reach at most the biseparable bound of the Mermin inequality for three parties and, for any number of parties, violate the Mermin family by exactly the factor of a single entangled pair. They are never genuinely multipartite nonlocal. Genuine multipartite nonlocality and computational universality are thus one resource for
fermions, the opposite of the stabilizer case. The mechanism is
fermion parity. The bound is monogamous and certifies non-Gaussianity from measured correlations alone. On superconducting processors we watch nonlocality beyond free
fermions switch on under an interaction between densities, confirm the monogamy law on 96
qubits, and measure the ground state of twelve interacting
fermions on a ring cross the bound as the interaction grows, detecting the charge density wave transition.
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Soft Condensed Matter
The hidden side of paintbrushes: a geometry shaped by power laws
Raphaelle Taub, Jérôme Crassous, Thomas Salez et al. (+2 more)
Since prehistoric times, painters have used brush-like tools made from animal and plant materials to apply pigments to rock surfaces. Over time, techniques for creating brushes evolved, and converged towards optimized shapes. Our study performed over hundreds of brushes reveals universal scaling laws. In particular, we uncover a relation between bristle length and diameter linked to the shape of the bristle ends, which governs their mechanical response with and without paint. For round brushes, we found that the size of the paint stain scales with the compression distance, meaning it only depends on the force applied by the painter and not on the mechanical responses of the brushes. These results shed light on the underlying universal physical principles governing brush design and their impact on artistic techniques.
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All authors Raphaelle Taub, Jérôme Crassous, Thomas Salez, Frédéric Restagno, Christophe Poulard
Strongly Correlated Electrons
Chiral quantum chaos around exponentially many zero modes in the quantum breakdown model
Kohei Kawabata, Kinya Guan and Hosho Katsura
The
quantum breakdown model is a model of randomly interacting
fermions, motivated by the physics of dielectric breakdown. Here, we establish classification of
symmetry and
quantum chaos in a zero-dimensional, all-to-all-interacting version of the
quantum breakdown model. It exhibits the $\mathbb{Z}_4$ periodicity with respect to the number of fermionic modes, reminiscent of the
symmetry classification of the Sachdev-Ye-Kitaev model. A unique feature of the
quantum breakdown model is that it realizes all the five classes with
chiral symmetry and hosts an exponentially large number of many-body zero modes protected by the
chiral index. We elucidate the separation and scaling of the spectral gap and demonstrate the
symmetry-enriched hard-edge spectral statistics as signatures of
quantum chaos in the
chiral symmetry classes.
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Statistical Mechanics
Square-root growth of operator entanglement in an integrable brickwork circuit
Balázs Pozsgay
It is widely expected that the von Neumann
entanglement of a local operator grows at most logarithmically in integrable many-body systems in infinite volume. We give a counterexample in a four-state brickwork
circuit whose gate is a permutation
matrix solving the constant Yang–Baxter equation. The von Neumann operator
entropy grows as $(\log2)\sqrt{t/\pi}+O(\log t)$, whereas fixed-index Rényi
entropies grow linearly below index one and logarithmically above it. At fixed relative
Hilbert–Schmidt error below one,
matrix product operator simulations require a bond dimension growing at least as $\exp(c\sqrt t)$ for some $c>0$.
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Instrumentation and Detectors
Measurement of the $^{39}$Ar specific activity in atmospheric argon with DArT at the Canfranc Underground Laboratory
P. Agnes, H. O. Back, S. Bharat et al. (+41 more)
We report the measurement of the $^{39}$Ar specific activity of atmospheric argon using DArT, a low-background single-phase
liquid-argon detector read out by cryogenic silicon photomultipliers, at the Canfranc Underground Laboratory (LSC) in Spain. DArT was first filled with atmospheric argon and then with a sample of underground argon of known radioactivity from the DarkSide-50 experiment. The underground argon serves as a background reference in this measurement, making the result robust because we do not rely on background simulations. We measure the $^{39}$Ar specific activity with both a cut-and-count method and a binned maximum-likelihood fit, yielding consistent results. We obtain $a_{\text{AAr}}= 0.955 \pm 0.008~\text{Bq}/\text{kg}$. This result agrees with previous measurements from other experiments and provides the most precise determination of the $^{39}$Ar specific activity in atmospheric argon to date. It also validates DArT as a key component of the DArTInArDM experiment at LSC, which aims to measure the $^{39}$Ar activity of the argon extracted from deep underground wells in Colorado (USA) for the Darkside-20k and LEGEND-1000 experiments at Laboratori Nazionali del Gran Sasso in Italy.
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All authors P. Agnes, H. O. Back, S. Bharat, W. M. Bonivento, M. Boulay, M. Caboni, N. Canci, N. Cargioli, P. Castello, S. Cebrián, L. Consiglio, R. Crampton, D. Diaz Mairena, D. Franco, I. Fuente-Ortega, F. Gabriele, D. Gahan, C. Galbiati, P. Garcia Abia, T. Hessel, S. Horikawa, A. Ianni, G. Korga, M. Kuźniak, L. Luzzi, A. Marasciulli, M. Martínez, P. Organtini, A. Ortiz de Solórzano, R. Pavarani, P. Pegoraro, V. Pesudo Fortes, M. Razeti, O. U. Rehman, L. Romero, D. Sablone, E. Sánchez García, R. Santorelli, C. Seoane, J. Sosiak, S. Sulis, C. Tierney, S. Tullio, G. Vera Díaz
Astrophysics of Galaxies
Yao-Yu Li, Shihong Liao, Yue-Lin Sming Tsai et al. (+1 more)
Primordial magnetic fields (PMFs), potentially generated during
cosmic inflation or early-universe phase transitions, can modify
cosmic structure formation by enhancing the post-recombination matter power spectrum. In this work, we investigate the impact of PMFs on
galaxy formation using a suite of high-resolution cosmological hydrodynamical simulations evolved to $z=0$. Our simulations are initialized with PMF-induced enhancements to the matter power spectrum and include more comprehensive baryonic subgrid models than previous work, incorporating both
stellar and AGN feedback. We find that PMFs systematically accelerate early structure formation, producing more abundant
halos and
galaxies, higher
baryon fractions, enhanced
star formation rates, and rapid growth of supermassive black holes at high
redshifts ($z \sim 10$). However, the resulting enhanced
stellar and AGN feedback efficiently processes and expels gas, reducing the late-time differences between PMF and standard $\Lambda$CDM models. The PMF signatures are therefore strongest at high
redshift and gradually weaken toward low
redshift as nonlinear
evolution and baryonic feedback dominate over the initial PMF-induced enhancements. The impact of PMFs depends strongly on the characteristic peak scale, $k_{\rm peak}$, of the initial power enhancement, with models yielding similar non-linear
evolution if they share a similar $k_{\rm peak}$, even when other PMF parameters differ. Our results highlight the critical role of comprehensive baryonic physics in accurately quantifying PMF signatures.
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All authors Yao-Yu Li, Shihong Liao, Yue-Lin Sming Tsai, Yi-Zhong Fan
Quantum Physics
Logical Operator Decomposition for Distance Analysis of Bivariate Bicycle Codes
Mohammad Rowshan and Simon Devitt
Bivariate bicycle (BB)
quantum codes are a prominent finite-length family of
quantum low-density parity-check codes, but their minimum distance is usually established numerically rather than read from the defining
polynomials. We study the $Z$-logical quotient $K/S$ over $\mathbb F_2[x,y]/(x^\ell-1,y^m-1)$ and show that it fits into a short exact sequence with an annihilator quotient as kernel and a colon quotient as cokernel. The sequence gives an explicit logical basis, a dimension formula, and a componentwise distance identity $d_Z=\min(d_{\mathcal A},d_{\mathcal C})$. Using the Frobenius structure of the finite group
algebra, we prove $r_{\mathcal A}=r_{\mathcal C}=k/2$ for every BB code, including repeated-root cases. The algebraic component of a logical class is distinct from the support shape of its lightest representatives: an annihilator class can have a lighter two-block representative, and a colon class can have a one-sided minimum. For lower bounds we show that every proper subset of a minimum-weight logical operator has nonzero syndrome, and that this property persists inside the colon component but not inside the annihilator component. A translation-anchored cluster search built on it proves the distances $4,6,10,10,12,18$ of the six standard BB codes of lengths $18$ to $288$ and enumerates every minimum-weight logical operator. The resulting census shows that $[[108,8,10]]$ is the only one of the six whose distance is attained in a single component, with $d_{\mathcal C}=10$ and $d_{\mathcal A}=12$.
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Quantum Physics
Spectrally Selective Charging of an Interacting Quantum Battery via an Anharmonic Mediator
Sujay Mondal, Anumita Mukhopadhyay, Siddhartha Dutta et al. (+1 more)
We investigate a finite-time
quantum-battery charging architecture in which a driven two-level working system transfers nonequilibrium resources to an interacting two-
qubit battery through a weakly anharmonic three-level mediator. Finite-time driving generates coherence and ergotropy, while excitation-number conservation organizes the transfer into distinct dynamical sectors. The mediator then provides spectrally selective charging channels: its lower transition enables nearly complete single-excitation transfer with negligible residual mediator energy, whereas initial mediator loading activates a cross-resonant two-excitation cascade toward the doubly excited battery state. The latter exhibits a modest reduction in transfer efficiency due to the unequal collective
matrix elements of the effective three-state chain. Detuning scans quantify the spectral tolerance, and the full mixed-state dynamics reveals distinct energy- and ergotropy-transfer profiles. Finite-time compression, thermal reset, and switching work close the cycle-level energy balance to numerical precision. The resulting scheme combines nonequilibrium resource generation, spectral selectivity, coherent multilevel charging, and thermodynamic cycle closure within a single architecture.
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All authors Sujay Mondal, Anumita Mukhopadhyay, Siddhartha Dutta, Abhijit Bandyopadhyay
Fluid Dynamics
Rigorous vertical averaging for pseudo-3D modeling of precipitation obstructed fluid flow
David Krach, Felix Weinhardt, Holger Class et al. (+2 more)
Computing effective hydraulic properties of porous materials with a dynamically changing pore morphology presents a complex and critical challenge in both theoretical and applied sciences. This paper presents a tool to effectively compute the intrinsic permeability k(x,t) for domains with both temporally and spatially varying pore structures, by utilizing a sample of snapshots of microfluidic experiments with calcium carbonate precipitation. To compute large domains at reasonable cost, a pseudo-3D Stokes solver with an additional viscous drag term is employed. In order to simulate the intricate domains with highly heterogeneous pore space, we derive vertically averaged governing equations including a vertically averaged drag term from scratch and without limiting assumptions. For exemplary precipitates (semi-spheres) of varying sizes within a rectangular channel with fixed solid boundaries, results are compared across multiple modeling approaches, each employing different drag force formulations. In addition, the performance of the derived models is examined for segments of an EICP experiment in terms of accuracy (comparison with 3D solvers) and computational efficiency. Finally, an entire experimental domain is used to demonstrate the capabilities offered by the solver thanks to its efficiency as well as accuracy and the permeability tensor k is computed and compared with experimental results. In all these applications, the vertically averaged drag term proves to be the optimal solution in terms of speed and accuracy, thus allowing for an efficient analysis of the non-uniformity of local fluid flow fluctuations resulting from alterations in the pore space.
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All authors David Krach, Felix Weinhardt, Holger Class, Holger Steeb, Martin Schneider
High Energy Physics (Phenomenology)
New Observables for Resonant and Non-Resonant New Physics Searches at Colliders
Julien Touchèque
The discovery of the
Higgs boson cemented the Standard Model of particle physics (SM) as we know it and observations have so far confirmed SM predictions. Now, too many beyond-the-Standard-Model (BSM) models can be explored to overcome the remaining shortcomings of the SM. As a result, generic models present a useful intermediary step to point towards the next extension of the SM probing multiple Ultraviolet models simultaneously. In this work, two examples are investigated. First, off-shell effects of potential heavy new particles are provided in the Standard Model Effective Field Theory (SMEFT) through higher dimensional operators. In particular, Charge-parity (CP)
symmetry violating contributions from Wilson coefficients are ranked by using U(1) global flavour
symmetries on CP-odd operators of the Warsaw basis. Asymmetries of simple triple products are proven to be more sensitive than the cross-section to these SMEFT operators and more efficient than most of the usual observables used in experiments. Then, on-shell effects of singlet and octet scalars of SUC(3) are independently searched for in four-top production. The signal consists of the associated production of a scalar with a top
quark pair and of pair production in the case of the octet producing boosted top-
quark pairs. The processes are generated at next-to-leading order in
quantum chromodynamics with a careful renormalisation procedure and the correct selection of loop diagrams. Using improvements in top-jet tagging techniques and in the main background simulation as well as a new technique to select the events, a new particle search is performed to constrain the respective mass and coupling to top
quarks of new resonances.
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Atmospheric and Oceanic Physics
Butterfly Effect Confirmed in Global AI Weather Models: Evidence from Tropical Cyclone Forecasting
Jeremy Cheuk-Hin Leung, Daosheng Xu, Weiye Yu et al. (+9 more)
A paradox recently emerged in artificial intelligence (AI) weather prediction research. While some claim AI weather models cannot simulate atmospheric butterfly effect, this conflicts with AI models' limited predictability and advances in AI ensemble
forecasting. This study demonstrates via counterexamples that the butterfly effect does exist in AI weather predictions. For Super Typhoon Khanun, AI predictions are constrained by a double-attractor system. Minor initial perturbations confined to two regions trigger state transitions between two local attractors, causing a 1006-km difference in the predicted storm position on Day 7. This behavior is consistent with numerical weather prediction models and observed in ~12% of tropical cyclones in the past 5 years. These findings verify AI's ability to capture atmospheric chaos and provide the physical basis for AI ensemble
forecasting.
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All authors Jeremy Cheuk-Hin Leung, Daosheng Xu, Weiye Yu, Shaojing Zhang, Xiaodong Zeng, Gaozhen Nie, Jie Feng, Jingchen Pu, Yi Li, Kaijun Ren, Qingcun Zeng, Banglin Zhang
Adaptation and Self-Organizing Systems
Recovery Random Walks and Extreme Events on Complex Networks
Karan Singh, Narendran R. V., V. K. Chandrasekar et al. (+1 more)
Extreme events are widely studied within simple random walk frameworks, where their probability is determined by the network structure and stationary walker distribution. Here, we propose a recovery random walk (RRW) model in which extreme events temporally `freeze' the nodes where they occur for a fixed duration $\Delta$ ($\Delta=0$ recovers the original model), trapping walkers and reducing the effective mobile population, thereby making the model more practical. We derive a first-principles description of this feedback and a delayed differential equation for the frozen-node fraction. This finite freezing produces an initial overshoot, followed by damped oscillatory relaxation to a steady state for the fraction of the frozen nodes. We find that freezing suppresses extreme event probability while preserving its degree dependence dynamics, and suppresses the EE frequency. Further, the analytical prediction for the fraction of the frozen nodes agrees closely with simulations. This model closely reflects real-world scenarios, yielding more practical EE statistics.
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All authors Karan Singh, Narendran R. V., V. K. Chandrasekar, D. V. Senthilkumar
Plasma Physics
Phase-Space Non-Integrability of Alpha Particles in Near-Omnigeneous Stellarators
A. L. Lachmann, A. R. Knyazev and E. J. Paul
In a burning
plasma, fusion-born alpha particles sustain the fusion reaction by heating the
plasma core. Alpha-particle confinement in stellarators is sensitive to both deviations from omnigeneity and time-dependent Alfvénic perturbations. Traditional Poincaré maps rely on
symmetry assumptions or dimensionality reductions that fail for stellarators with quasisymmetry (QS) error or multi-harmonic Alfvénic perturbations. To address these challenges, we investigate weighted Birkhoff averaging (WBA) as a diagnostic to detect the onset of chaos in guiding-centre trajectories subject to general
magnetic perturbations. WBA exploits the super-convergence of time averages along quasiperiodic orbits, discriminating regular from chaotic trajectories using any smooth observable rather than an exact invariant of motion. Applying WBA to the canonical momentum $P_\eta$, we show that convergence tracks underlying orbit regularity even when quasisymmetry is imperfect and $P_\eta$ is not strictly conserved. Convergence is measured by the digit accuracy of the weighted average along guiding-centre orbits in fields with imperfect omnigeneity, with and without Alfvén eigenmodes computed using AE3D. We use this diagnostic to map phase-space chaos as a function of
equilibrium invariants to identify transport barriers in unperturbed and perturbed stellarator
equilibria. This work demonstrates that chaos induced by many Alfvén harmonics is often not apparent from the largest harmonic alone. We also find evidence that the onset of chaotic behaviour is sensitive to the local radial profile of the wave and not only to its amplitude at the resonance.
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Quantum Physics
Efficient Learning of Fermionic Magic States under Free-Fermion Evolution
Jiwon Heo, Myeongjin Shin and Changhun Oh
We establish efficient learning for a family of fermionic magic states under unknown number-conserving free-
fermion evolution. Each input block has a definite particle number and is a superposition of Fock states, with occupied mode sets disjoint both within and across blocks. The key idea is to exploit the spectral structure of particle reduced density
matrices (RDMs) to separate contributions from individual blocks from those involving several blocks, allowing us to reconstruct the hidden block structure. For a fixed upper bound on the particle number per block, our
algorithm uses single-copy measurements and
polynomial sample and classical computational complexity to recover a compact description of the state with prescribed fidelity and high probability, without prior knowledge of the block decomposition or the
evolution. RDMs up to this upper bound suffice for reconstruction. We further show that this RDM order is necessary in general: two orthogonal states in the family can have identical RDMs at every lower order. These results show that an extensive number of non-Gaussian blocks can be compatible with efficient state learning.
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Statistical Mechanics · Cross-listed from stat.ML
A Dynamical Theory of LoRA in Continual Learning
Théo Marchetta, Filippo Alessandroni, Alessandro Breccia et al. (+2 more)
Despite the widespread use of Low-Rank Adaptation (LoRA), little is known about its dynamics in continual learning and the mechanisms by which low-rank updates affect catastrophic forgetting. We provide an asymptotically exact dynamical characterization of LoRA in a solvable two-task teacher-student model. In the high-dimensional online-learning limit, we derive a closed system of ordinary differential equations for a finite set of macroscopic order parameters, yielding exact expressions for the generalization errors throughout both the initial Task 1 learning phase and the subsequent LoRA fine-tuning on Task 2. The theory quantitatively matches finite-dimensional simulations and exposes two characteristic effects of LoRA: low-rank adaptation reduces interference with features learned on the first task, but its initialization slows adaptation to the second task. Building on this mechanistic picture, we analyze a state-dependent masking strategy that freezes hidden units carrying the strongest first-task representations and restricts adaptation to the complementary subspace. This structural partitioning markedly reduces forgetting, while preserving plasticity on the new task. Our framework further clarifies the role of adapter rank: transfer improves only up to the intrinsic dimensionality of the target task and saturates beyond it, while forgetting continues to grow with rank. These results provide a dynamical and
geometric account of how low-rank adaptation organizes information across sequential tasks and are qualitatively reproduced on a sequential MNIST
benchmark.
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All authors Théo Marchetta, Filippo Alessandroni, Alessandro Breccia, Alessandro Ingrosso, Federica Gerace