Disordered Systems and Neural Networks · Cross-listed from stat.ML
A theory of learning data statistics in diffusion models, from easy to hard
Lorenzo Bardone, Claudia Merger and Sebastian Goldt
While
diffusion models have emerged as a powerful class of generative models, their learning dynamics remain poorly understood. We address this issue first by empirically showing that standard
diffusion models trained on natural images exhibit a distributional simplicity bias, learning simple, pair-wise input statistics before specializing to higher-order correlations. We reproduce this behaviour in simple denoisers trained on a minimal data model, the mixed cumulant model, where we precisely control both pair-wise and higher-order correlations of the inputs. We identify a scalar invariant of the model that governs the sample complexity of learning pair-wise and higher-order correlations that we call the
diffusion information exponent, in analogy to related invariants in different learning paradigms. Using this invariant, we prove that the denoiser learns simple, pair-wise statistics of the inputs at linear sample complexity, while more complex higher-order statistics, such as the fourth cumulant, require at least cubic sample complexity. We also prove that the sample complexity of learning the fourth cumulant is linear if pair-wise and higher-order statistics share a correlated latent structure. Our work describes a key mechanism for how
diffusion models can learn distributions of increasing complexity.
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Other Condensed Matter
Andrei Nikitchenko and Guido Burkard
Dispersively coupled distant
qubits in a shared cavity can become entangled through virtual
photon exchange with energy-conserving phase
evolution of their
quantum states. This interaction can potentially be accelerated by operating on resonance, allowing for the exchange of real
photons. In this theoretical study, we examine
photon-mediated
entanglement between two distant
spins of electrons confined in double
quantum dots formed in a Si/SiGe
heterostructure. We calculate the dynamics of the combined system comprised of both
spin qubits and the cavity, assuming that both
spin qubits can be tuned into and out of resonance with the host cavity. We demonstrate that the exchange of real
photons between the two
spin qubits can result in rapid
entanglement that is robust against decoherence. These results pave the way for the development of
quantum gates on resonantly coupled distant
semiconductor spin qubits.
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Materials Science
Neutron-Induced Enhancement of Ion Transport Through Lithium-Ion Battery Materials
Ha M. Nguyen, Carson D. Ziemke, David Stalla et al. (+9 more)
Polycrystalline solid-state ionic conductors (SSICs) are essential energy materials for all-solid-state Li-ion batteries. To date, achieving a room-temperature ionic conductivity of solid electrolytes comparable to that of their
liquid counterparts remains a critical challenge. Here, we experimentally demonstrate that thermal
neutron irradiation can offer an innovative strategy in that
neutron-induced modification in an SSIC model (LiBO$_{2}$ as an effective cathode coating) can facilitate ion transport through the material, enhancing its ionic conductivity. The central concept is that high-flux ($\sim 10^{9}\text{ neutrons}\cdot \text{cm}^{-2}\cdot \text{s}^{-1}$) thermal
neutrons ($\sim \text{25 meV}$) selectively transmute strong
neutron absorbers [which are $^{10}$B (3840 barns) and $^{6}$Li (940 barns) isotopes and present in their natural abundances of $\sim 19.9\%$ and $\sim 7.5\%$, respectively, in polycrystalline grains of LiBO$_2$] to generate
lattice vacancies without compromising their crystallographic long-range order. In addition, by-product gamma
photons emitted from $^{10}$B transmutation free electrons to stop atomic displacement and simultaneously neutralize the space charge built up by positively-charged oxygen vacancies at grain boundaries. As a result, the ionic conductivity is increased by nearly 20% for the grains and more than 80% for the grain boundaries. This study validates theoretical predictions and highlights a vital strategy for boosting ion transport in ionic solids. Overall, this novel approach establishes a new revenue for broader applications and greater enhancements of advanced functional materials in their related solid-state ionic devices, including all-solid-state lithium-ion batteries.
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All authors Ha M. Nguyen, Carson D. Ziemke, David Stalla, Tymofii Pieshkov, Thi-Hien Truong, Min Su, Bikash Saha, Narendirakumar Narayanan, Carlos Wexler, John Gahl, Yangchuan Xing, Thomas W. Heitmann
Superconductivity
Finite-momentum superconductivity with singlet-triplet mixing in an altermagnetic metal: A pairing instability analysis
Hui Hu, Zhao Liu, Jia Wang et al. (+2 more)
We analyze the pairing instability of an altermagnetic metal on a square
lattice driven by an attractive nearest-neighbor interaction. This interaction enables multiple pairing channels, including even-parity extended $s$-wave and $d$-wave states, as well as two odd-parity $p$-wave channels. We verify that altermagnetic
spin-splitting in the single-particle dispersion gives rise to finite-momentum pairing between electrons with unlike
spins, in agreement with earlier predictions. Quite unexpectedly, this pairing typically emerges across multiple channels with mixed parity. Consequently, the resulting finite-momentum Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting phase is expected to exhibit a multi-component order parameter featuring singlet-triplet mixing. We examine several forms of altermagnetism, specifically $d_{xy}$-wave and $d_{x^{2}-y^{2}}$-wave altermagnetic couplings, and present the corresponding phase diagrams. Additionally, we study triplet pairing between electrons with identical
spins and find that it always occurs at zero center-of-mass momentum. Although it is unfavorable in the regime of weak altermagnetic coupling and low electron filling, it can dominate the phase diagram when the altermagnetic coupling is sufficiently strong. The influence of on-site attractive interactions on mixed-parity pairing is also explored.
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All authors Hui Hu, Zhao Liu, Jia Wang, Xia-Ji Liu, Yoji Ohashi
Materials Science
Magnetic-field-induced magnon portfolio in a van der Waals magnet
T. Riccardi, F. Le Mardélé, L.A. Veyrat de Lachenal et al. (+12 more)
Magnonic excitations are investigated in chromium oxychloride (CrOCl), a van der Waal (vdW) antiferromagnet prone to a multitude of
magnetic phase transitions, with absorption experiments in a broad continuous energy range. At low
magnetic fields, the
magnon spectra show a strong bi-axial anisotropy and inform on the relative weights of the effective exchange coupling and the system anisotropies. As the
magnetic field increases,
magnons characteristic of a canted phase are first observed, with peculiarities attributed to in-plane anisotropies and
magnon-
magnon coupling. Subsequently, a hysteretic
magnon spectrum appears as the system transitions to a ferrimagnetic state, with two new
magnon branches partly coexisting with the lower energy canted phase branch, indicating the formation of spatially separated
magnetic phases. Further changes in the
magnon spectrum in higher
magnetic fields accompany transitions to the different canted
magnetic phases previously reported. Our experiments show that competing exchange interactions and ground states broaden the options to generate different kinds of magnonic excitations in the same vdW material upon the variation of external parameters.
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All authors T. Riccardi, F. Le Mardélé, L.A. Veyrat de Lachenal, A. Pawbake, I. Plutnarova, Z. Sofer, G. Jacquet, F. Petot, A. Saùl, B. Grémaud, A. L. Barra, M. Orlita, J. Coraux, C. Faugeras, B. A. Piot
Materials Science
Quantifying Perovskite Solar Cell Degradation via Machine Learning from Spatially Resolved Multimodal Luminescence Time Series
Giulio Barletta, Simon Ternes, Saif Ali et al. (+7 more)
Perovskite
solar cells achieve remarkable power conversion efficiencies, yet operational stability remains a major barrier to large-scale deployment. Reliable and rapid assessment of device state of health is therefore essential. Conventional electrical diagnostics, such as illuminated current-voltage (J–V) sweeps, provide accurate performance metrics but are time-consuming and do not resolve spatially localized degradation, motivating non-invasive imaging-based alternatives. A deep-learning framework is introduced to estimate PSC efficiency retention, $R_\mathrm{PCE}=\mathrm{PCE}_t/\mathrm{PCE}_0$, directly from
multimodal luminescence imaging acquired during device aging. Each sample combines electroluminescence (EL), open-
circuit photoluminescence (PLoc), and short-
circuit photoluminescence (PLsc) at an aged state with device-specific reference images at $t=0$, enabling learning of degradation-relevant spatial changes. LumPerNet, a compact convolutional neural network, is benchmarked against a spatially homogenized control in which each luminescence channel is replaced by its spatial average while retaining the same learning framework and leakage-aware protocol. The comparison indicates that global luminescence
evolution contains most of the predictive signal, while spatial information provides a secondary contribution to robustness. These results establish spatially resolved luminescence imaging as a practical route for accelerated stability testing and non-invasive degradation monitoring in perovskite photovoltaics.
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All authors Giulio Barletta, Simon Ternes, Saif Ali, Zohair Abbas, Chiara Ostendi, Marialucia D'Addio, Erica Magliano, Pietro Asinari, Eliodoro Chiavazzo, Aldo Di Carlo
Disordered Systems and Neural Networks
Continuous unitary transformations using tensor network representations access the full many-body localized spectrum
Qiyu Liu, Jan-Niklas Herre, Dante M. Kennes et al. (+1 more)
We develop variational continuous
unitary transformations (VCUTs), which integrate Wegner-Wilson flow equations with tensor network techniques to approximately diagonalize many-body localized (MBL)
Hamiltonians. The diagonalizing
unitary is represented as a
matrix product operator whose bond dimension controls the accuracy. For the disordered Heisenberg chain, VCUTs accurately reproduces the full spectrum across the ergodic-to-MBL crossover at small system sizes and scales to $L = 48$ sites. Beyond eigenenergies, the method can track the spatial
entanglement structure of the diagonalizing
unitary $U(l)$ at each flow step, enabling identification of local integrals of motion deep in the MBL phase.
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All authors Qiyu Liu, Jan-Niklas Herre, Dante M. Kennes, Christoph Karrasch
Strongly Correlated Electrons
Many-body correlations in Floquet steady-states: Frequency-resolved renormalization group of the driven Anderson impurity
Jan-Niklas Herre, Christoph Karrasch and Dante M. Kennes
We introduce a functional renormalization group framework formulated directly in the Floquet steady-state that systematically incorporates frequency-dependent interaction effects. By retaining the frequency structure of the two-particle vertex up to second order in interaction strength, our approach provides controlled access to dynamical response functions and nonequilibrium transport in driven, interacting systems. Using the periodically driven single-
impurity Anderson model as a paradigmatic example, we
benchmark our results against state-of-the-art Floquet Green's function methods and find quantitative agreement for finite-frequency observables up to intermediate interaction strengths. Remarkably, we also show that static properties are often captured reliably by much simpler approximations, suggesting practical pathways for modeling driven
quantum materials. Finally, we demonstrate that although periodic driving of the dot strongly broadens the Kondo resonance through inelastic scattering, it leaves the many-body Kondo cloud largely intact. This robustness suppresses Floquet replicas of the Kondo peak and leads to a partial persistence of Kondo pinning, highlighting the resilience of emergent many-body correlations under local periodic driving.
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Soft Condensed Matter
Cell-induced wrinkling patterns on soft substrates
Aleksandra Ardaševa, Varun Venkatesh, Daiki Matsunaga et al. (+2 more)
Cells exert traction forces on compliant substrates and can induce surface instabilities that appear as characteristic wrinkling patterns. Here, we develop a mechanical description of
cell-induced wrinkling on soft substrates using a thin film elastic framework based on the Föppl-von Kármán equations coupled to a phase-field model of a single
cell. We model in-plane contractile stresses driven by cellular activity and study how their magnitude, spatial distribution, and
symmetry determine the onset of wrinkling and the resulting pattern selection. The theory predicts transitions between distinct morphologies, such as radial, circumferential, and anisotropic wrinkle arrangements, and provides scaling relations for wrinkle wavelength and amplitude as functions of elastic parameters and imposed cellular forcing. We compare these predictions with available experimental observations of
cell-driven wrinkling on compliant gels and find good agreement for both qualitative pattern classes and quantitative wavelength trends. Our results offer a minimal modelling framework to interpret wrinkling assays and connect observed surface patterns to underlying cellular forces.
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All authors Aleksandra Ardaševa, Varun Venkatesh, Daiki Matsunaga, Shinji Deguchi, Amin Doostmohammadi
Materials Science
Fangzhou Zhao, Carlos Mejuto-Zaera, Angel Rubio et al. (+1 more)
Excitons in the weakly interacting regime can be well-described by many-body perturbation theories such as the Bethe-Salpeter equation formalism. However, for materials such as transition metal dichalcogenides moiré
heterostructures under strong illumination, with the emergence of dense excitonic states, the strong correlation and
entanglement between electrons and holes may cause the many-body perturbation method to fail, and
excitons may not be treated in the bosonic picture, but exhibit fermionic behaviors. In our work, we investigate the phase space where
excitons, and the electrons and holes which constitute them, are weakly or strongly entangled, as well as their binding for different interaction profiles and the degree of localization of the electrons and holes. We corroborate the validity of using many-body perturbation theory in the
exciton with interactions. Our work provides a general way to analyze the correlation and
entanglement of multi-particle excitations in many-body systems, and gives a more comprehensive understanding of different phases for
exciton entanglement and interactions in 1D systems.
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All authors Fangzhou Zhao, Carlos Mejuto-Zaera, Angel Rubio, Vojtěch Vlček
Materials Science
Optimized growth of large-size, high quality $\text{ZrTe}_5$ single crystals enabling clear quantum oscillations in electrical transport
Hong Du, Yu Cao, Jiahao Chen et al. (+3 more)
Quantum oscillation with nontrivial Berry phase is one of the characteristics of topological materials. As a Dirac semimetal candidate, zirconium pentatelluride ($\text{ZrTe}_5$) stands out as an intriguing material for investigating topological phase transitions and Dirac
fermion physics; however, the extreme sensitivity of its electronic properties to stoichiometric variations and crystalline defects has hindered consistent experimental observation. Here, we report an optimized Te-flux synthesis method designed to produce centimeter-scale, high-quality single
crystals meanwhile minimizing extrinsic carrier contamination. Comprehensive morphology, structural and chemical characterizations, including scanning electron microscopy, Laue backscattering and Rietveld refinement, confirm a high-purity $Cmcm$ phase with excellent crystallinity. Furthermore, magnetotransport measurements reveal a remarkably low Shubnikov-de Haas oscillation onset field ($B_{int} \approx 0.38$ T) with an ultra-high mobility of $5.58\times10^5$cm$^2$V$^{-1}$s$^{-1}$ and access to the the
quantum limit at $B \approx 1.3$ T, attesting to the superior crystalline quality and the efficacy of this growth optimization. These results demonstrate that growth control is crucial for stabilizing intrinsic electronic behavior in $\text{ZrTe}_5$, establishing a robust platform for exploring topological phase transitions and exotic
quantum phenomena in topological semimetals.
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All authors Hong Du, Yu Cao, Jiahao Chen, Tian Liang, Liang Liu, Ruidan Zhong
Materials Science
RF magnetron sputtering deposition of multilayers optical filters for ultra-broadband applications with a large number of thin layers
Maxime Duris, Bryan Horcholle, Cédric Frilay et al. (+6 more)
We present recent achievement on manufacturing optical filter and multilayers done with two complementary RF magnetron sputtering approaches: deposition duration control and in situ optical reflectance monitoring. Those approaches were greatly improved thanks to ellipsometry and spectrophotometry cross-studies of optical refractive indexes of Nb2O5, TiO2 and SiO2 materials grown using two sputtering systems. At the same time, we conducted deposition studies of these three materials which have increased the manufacturing reliability and allowed us to consider developing complex optical multilayers with more than 100 layers.
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All authors Maxime Duris, Bryan Horcholle, Cédric Frilay, C. Labbe, Xavier Portier, Philippe Marie, Sylvain Duprey, Franck Lemarié, Julien Cardin
Strongly Correlated Electrons
Ab initio screening of quantum frustrated materials with kagome and triangular geometries
Byeong-Hyeon Jeong, Hee Seung Kim, SungBin Lee et al. (+1 more)
Geometrical frustration is a powerful route to realize exotic phases such as
quantum spin liquids. Despite extensive efforts, systematic searches targeting specific frustration motifs and their potential to host unconventional
magnetic ground states remain rare, thus highlighting the need for a more focused and predictive materials discovery approach. Here we present a new strategy combining high-throughput first-principles calculations,
magnetic force theory, and
spin Hamiltonian analysis. Starting from the 150,000 material database, we catalogue candidate materials that may host competing exchange interactions and new types of
magnetic states with the focus on kagome or triangular
lattices. Our workflow not only reproduces the majority of known frustrated
magnetic materials, validating our approach, but also predicts novel candidate compounds with targeted frustration profiles that have not yet been experimentally synthesized. Among these, we identify six promising new materials: one triangular
lattice compound, KMgNiIO6, and five kagome
lattice compounds; Li4Fe3WO8, Li2V3F8, Li5VP2(O4F)2, and Li2MgCo3O8 (P2/m and C2/m). For each candidate, we identify detailed
magnetic properties and further propose their potential
magnetic ground states, revealing that some of them may host entirely new
magnetic phases driven by their distinct frustration characteristics.
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All authors Byeong-Hyeon Jeong, Hee Seung Kim, SungBin Lee, Myung Joon Han
Mesoscale and Nanoscale Physics
Phonon-Induced Zero-bias Currents in Solids
Masao Ogata and Hidetoshi Fukuyama
Zero-bias current induced by injected
phonons in metals and one-dimensional charge density wave (CDW) systems attached on the surface of the piezoelectric substrate is investigated microscopically based on the second order response theory. In contrast to the shift currents discovered by von Baltz and Kraut in which the zero-bias current is induced by AC electric field in systems without inversion
symmetry, propagating
phonons break the inversion
symmetry in the presesnt case. The effects of both deformation potential and piezoelectric potential are taken into account. In the CDW system, zero-bias current appears below the transition temperature and its magnitude strongly depends on the position of the chemical potential. Possible experimental consequences are discussed.
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Materials Science
Slow spin-lattice relaxation dynamics in YbVO4 revealed by extended thermal impedance spectroscopy from AC susceptibility and AC magnetocaloric measurements
Yuntian Li, Jiayi Hu, Dominic Petruzzi et al. (+4 more)
Alternating (AC)
magnetic fields can induce not only an alternating magnetization in materials, but also an alternating temperature via the magnetocaloric effect. The latter effect is typically neglected when performing AC susceptibility measurements, but consideration of both effects on an equal footing is necessary in order to reliably distinguish between internal and external causes of
magnetic response and accurately extract quantitative information about relaxation processes. In order to address this, we have developed a method to measure the AC magnetocaloric effect that is compatible with AC susceptibility measurements, and also a framework to analyze these data in combination. We demonstrate the efficacy of this approach using YbVO4, a material for which strong single-ion anisotropy leads to slow
spin-
lattice relaxation at low temperatures via a
phonon bottleneck effect. We report AC
magnetic susceptibility and AC magnetocaloric effect measurements for this material as a function of field and frequency at a temperature of 3 K. We analyze the data using a discretized thermal model, and extract the field-dependence of the intrinsic
spin-
lattice relaxation rate. This demonstration experiment illustrates a general approach to quantitatively address multiple measured quantities in driven systems using a unified thermal
circuit analysis. The thermal analysis methods presented in this report can be extended to study other
magnetic, dielectric, and elastic materials exhibiting a complex response to an external driving field in the presence of internal and external relaxation, particularly when an energy dissipation process is within an accessible frequency regime.
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All authors Yuntian Li, Jiayi Hu, Dominic Petruzzi, Linda Ye, Mark P. Zic, Arkady Shekhter, Ian R. Fisher
Mesoscale and Nanoscale Physics
Torsional oscillation of carbon nanotubes driven by electron spins
Koji Yamada, Wataru Izumida, Mamoru Matsuo et al. (+1 more)
We theoretically investigate the current-induced excitation of torsional vibrations in a suspended carbon nanotube (CNT)
quantum dot. By considering a CNT clamped between half-metallic
ferromagnetic electrodes with an antiparallel magnetization configuration, we demonstrate that the
spin-rotation coupling (SRC) enables the transfer of angular momentum from electron
spins to the mechanical torsional mode under a constant source-drain voltage. Using a master-equation approach to analyze the coupled dynamics of the dot levels and a quantized torsional oscillator, we evaluate the steady-state current and
phonon distribution. We find that when the Zeeman splitting matches the torsional
phonon energy, the system exhibits sharp resonant behavior in the current, accompanied by a significant increase in the
phonon population. Our estimates for realistic device parameters indicate that this
spin-driven mechanism can drive CNT torsional vibrations with detectable amplitudes. This work provides a theoretical basis for resonant current-controlled actuation of CNT torsional modes via SRC-mediated transfer of
spin angular momentum.
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All authors Koji Yamada, Wataru Izumida, Mamoru Matsuo, Takeo Kato
Strongly Correlated Electrons
Discovery of a hybridization-wave electronic order in a van der Waals Kondo lattice
Lu Cao, Jiefei Shi, Lanxin Liu et al. (+6 more)
Kondo
lattice systems, in which localized
magnetic moments coherently hybridize with itinerant electrons, exhibit a rich landscape of emergent
quantum phenomena. Within this framework, the hybridization strength itself has been theoretically proposed as a spatially modulated order parameter, giving rise to a so-called hybridization wave. However, direct experimental evidence of this
quantum state has remained an outstanding challenge. Here, we report the direct observation of a hybridization wave in the layered transition metal dichalcogenide 6R-TaS2, a naturally occurring
heterostructure composed of alternating 1T- and 1H-TaS2 layers. Using scanning tunneling microscopy and spectroscopy (STM/STS), we identify the hybridization gap in 1T layer, demonstrating the establishment of a coherent Kondo
lattice. Notably, we discover that the hybridization gap present a uniaxial unit-
cell doubling modulation, which breaks the both translational and rotational
symmetries of the underlying
Star-of-David superlattice. Such unit-
cell doubling is not caused by structural topography, and therefore, constitutes the real-space visualization of the hybridization-wave order. Furthermore, the hybridization wave correlates with an energy-dependent nematic order that shares the same periodicity and orientation, revealing intertwined electronic instabilities. Our findings not only validate a long-standing prediction but also establish layer-engineered van der Waals materials as a versatile platform for exploring and controlling hybridization-driven
quantum phases.
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All authors Lu Cao, Jiefei Shi, Lanxin Liu, Xuan Luo, Yu-Ping Sun, Yi-feng Yang, Yugui Yao, Jinhai Mao, Yuhang Jiang
Strongly Correlated Electrons
Elastoresistivity Signatures of Nematic Fluctuations in Layered Antiferromagnet CoTa3S6
Tao Lu, Zili Feng, Mengxing Ye et al. (+2 more)
Nematic phases that break rotational
symmetry are widely observed in
quantum materials, and clarifying their origin and relationship with other
symmetry-breaking phases remains an important but challenging task. In this work, we investigate nematic fluctuations in CoTa$_3$S$_6$ using elastoresistivity experiments to resolve the nature of the proposed nematic phase intertwined with collinear and non-coplanar
antiferromagnetic orders. We observe a divergence-like antisymmetric elastoresistivity that rapidly develops below the stripe
antiferromagnetic transition, consistent with a distinct nematic degree of freedom coupled to the
magnetic order. While nematic fluctuations are strongly modulated by an external out-of-plane
magnetic field and the onset temperature of resistivity anisotropy shows pronounced strain dependence, the
antiferromagnetic transition temperatures remain nearly unchanged under either
magnetic field or strain. Additionally, complementary magnetoresistance measurements reveal characteristic signatures of three-state nematicity in a hexagonal system. Our findings demonstrate CoTa$_3$S$_6$ as a unique case of intertwined nematic and AFM orders with distinct origins.
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All authors Tao Lu, Zili Feng, Mengxing Ye, Takashi Kurumaji, Linda Ye
Mesoscale and Nanoscale Physics
Linear Magnetoresistance as a Probe of the Neel Vector in Altermagnets with Vanishing Anomalous Hall Effect
Kamal Das and Binghai Yan
Despite time-reversal breaking in momentum space, several altermagnets remain electrically silent to the primary characterization tool anomalous
Hall effect, due to crystalline
symmetries, jeopardizing their experimental identification. Here, we show that time-reversal odd magnetoresistance exhibiting butterfly-like hysteresis with linear
magnetic field dependence near the zero field provides a robust transport signature of altermagnetism even when the anomalous
Hall effect vanishes. Using semiclassical theory and
symmetry analysis, we demonstrate that this effect is generic across altermagnets and validate it through first-principles calculations in CrSb. Our results establish linear magnetoresistance as an alternative detection of the Berry
curvature and Neel order in unconventional antiferromagnets.
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Soft Condensed Matter
Memory-aware acceleration of orientational dynamics in nanoparticle suspensions
Miguel Ibáñez, Raúl A. Rica-Alarcón and María L. Jiménez
The relaxation of
stochastic systems after sudden perturbations is constrained by speed limits and often reveals
memory effects that hinder attempts to accelerate their dynamics. Here we demonstrate Kovacs-type nonmonotonic relaxation in the electro-orientation of non-spherical nanoparticles and show how this
memory effect limits simple acceleration protocols. Experimentally, the orientational dynamics is monitored optically through field-induced birefringence, which is proportional to the nematic order parameter. When an AC electric field is first set to an extreme value until the birefringence reaches its target and is then switched to the target field (matched two-step protocol), the relaxation exhibits a characteristic Kovacs shoulder. We interpret this behavior within a theoretical framework based on the Smoluchowski equation for the orientational probability density. In the high-frequency AC regime, orientational relaxation is governed by induced dipoles, and the observed
memory effect originates from polydispersity, which generates a spectrum of rotational
diffusion coefficients and hence multiscale relaxation. Building on this insight, we design protocols that mitigate the detrimental effect of
memory by sequentially suppressing the slowest active relaxation mode. Experiments on nanoparticle suspensions with different properties confirm these mechanisms, and we demonstrate substantial reductions in relaxation time compared with single quenches and matched two-step protocols with NaMt suspensions. More broadly, these results illustrate how
memory effects emerge when many degrees of freedom are steered with a single control parameter and provide an experimentally accessible strategy for controlling multiscale
stochastic dynamics.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Probing many-body localization crossover in quasiperiodic Floquet circuits on a quantum processor
Kazuma Nagao, Tomonori Shirakawa, Rongyang Sun et al. (+2 more)
Many-body localization (MBL) provides a mechanism by which interacting
quantum systems evade thermalization, leading to persistent
memory of initial conditions and slow
entanglement growth. Probing these dynamical signatures in large systems and at long
evolution times remains challenging for both classical simulations and current
quantum devices. Here we experimentally investigate the ergodic-MBL crossover in quasiperiodic Floquet Ising systems using up to 144
qubits on an IBM
Quantum processor. By implementing deep Floquet
circuits reaching up to 5000 cycles, we access long-time many-body dynamics beyond the regime explored in previous
quantum computing experiments. Measurements of autocorrelation functions reveal a smooth crossover from rapid thermalization at weak quasiperiodic potential strength to persistent correlations in the strong-disorder regime. Notably, in addition to the one-dimensional system, we also observe clear signatures consistent with localization behavior in the two-dimensional system. Furthermore, the
quantum Fisher information exhibits logarithmic growth over thousands of Floquet cycles, providing evidence for slow
entanglement spreading characteristic of the MBL regime. These results demonstrate that programmable
quantum processors can serve as experimental platforms for probing nonergodic
quantum many-body dynamics and exploring localization phenomena in regimes beyond the reach of classical simulations.
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All authors Kazuma Nagao, Tomonori Shirakawa, Rongyang Sun, Peter Prelovšek, Seiji Yunoki
Soft Condensed Matter · Cross-listed from quant-ph
Active quantum matter from monitored pure-state dynamics
Jacob F. Steiner, Felix von Oppen and Reinhold Egger
Quantum many-body systems coupled to out-of-
equilibrium reservoirs can behave as active matter and exhibit signs of flocking. However, the resulting steady states are highly mixed and carry only weak
quantum signatures. We show that signatures of active matter also arise in ensembles of pure states undergoing monitored
quantum dynamics. We consider a spinful Luttinger
liquid subject to measurement processes that shuffle
spin-up particles to the left and
spin-down particles to the right. For weak monitoring strengths and
ferromagnetic spin interactions, we find power-law
quantum correlations between
spin density and charge current, which we identify as a hallmark of active
quantum matter. The monitoring plays a dual role, generating the
quantum active correlations for weak strengths while driving a Berezinskii-Kosterlitz-Thouless (BKT) phase transition to a shortrange correlated state at larger strengths.
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Statistical Mechanics · Cross-listed from quant-ph
Critical behaviors of magic and participation entropy at measurement induced phase transitions
Eliot Heinrich, Hanchen Liu, Tianci Zhou et al. (+1 more)
We study the participation and stabilizer
entropy of non-
unitary quantum circuit dynamics, focusing on the critical line that separates the low-
entanglement spin-glass phase and the paramagnetic phase. Along this critical line, the
entanglement has a logarithmic scaling, which enables us to access the critical regime using large-scale
matrix product state simulations with modest bond dimension. We find that both the participation
entropy and stabilizer
entropy exhibit critical slowing down: their saturation time scales linearly with the system size, in stark contrast to purely
unitary dynamics, where saturation occurs on logarithmic time scales. In addition, we study bipartite participation and stabilizer mutual information, and find that it shows similar scaling behavior to the
entanglement entropy. Finally, by analyzing the participation
entropy of several paradigmatic Clifford
circuits, we identify similar slow dynamical behavior near their respective critical points.
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All authors Eliot Heinrich, Hanchen Liu, Tianci Zhou, Xiao Chen
Strongly Correlated Electrons
Elucidating magnetic structure with optical dopants: erbium-doped Gd$_2$SiO$_5$
Luke S. Trainor, Masaya Hiraishi, J.-R. Soh et al. (+1 more)
The narrowness of the optical transitions of rare-earth-ion dopants makes them highly sensitive probes of their environment. We measured the optical transitions Er$^{3+}$ dopants to determine the previously unknown
magnetic ordering of Gd$_{2}$SiO$_{5}$ – a promising host for
quantum applications of rare-earth dopants. By measuring the transitions'
magnetic-field dependence we determined an
antiferromagnetic ordering with
spins oriented along or slightly canted from the
crystal's $a^*$ axis. The optical transitions are narrower than the coupling to gadolinium
spins revealing information about the coupling strengths. We further optically measured a Néel temperature of $1.86\pm0.01_\mathrm{stat.}\pm0.07_\mathrm{syst.}$ K, and assembled a phase diagram in applied field and temperature showcasing a triple point where two gadolinium sites order semi-independently from each other. At high applied field the erbium dopants show long optical coherence times up to 0.4 ms at 3 T; at low fields these are probably limited by three low-frequency
magnon modes below 10 GHz, observed directly. This study can be used to
benchmark a method of
magnetic structure determination.
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All authors Luke S. Trainor, Masaya Hiraishi, J.-R. Soh, Jevon J. Longdell
Statistical Mechanics · Cross-listed from quant-ph
Pointwise mutual information bounded by stochastic Fisher information
Pedro B. Melo
How much information about an unknown parameter can be assigned to one realized outcome, and how is that information constrained by the sensitivity of the same outcome? We derive upper bounds on the pointwise mutual information in terms of the
stochastic Fisher information, both for parameters in a bounded interval and for sufficiently regular differentiable priors, and state the corresponding saturation conditions. Averaging the pointwise inequality and applying Jensen's inequality twice yields the known mutual-information–Fisher-information bound, while making explicit the outcome dependence discarded by the ensemble description. We illustrate the classical result using the instantaneous position of an overdamped Langevin particle as the observed outcome. For a fixed, parameter-independent
quantum measurement, the
stochastic Fisher information is further bounded by the conditional
quantum Fisher information (CQFI), whose probability-weighted mean is the
quantum Fisher information. A thermal-
qubit field-sensing example evaluates this finite-prior bound deterministically from exact $2\times2$
matrices and, separately, decomposes the projected SLD second moment into population, coherent, and interference contributions. The interference contribution can be negative for an individual probe direction and has zero unweighted trace, but it is not itself an operational measure of readout quality. Neither the CQFI nor its mean selects a measurement basis: the latter is measurement-independent, whereas the relevant basis-dependent local objective is the classical Fisher information of the chosen measurement.
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Superconductivity
Spectroscopic Studies of two-dimensional Superconductivity
Qiang-Jun Cheng, Xu-Cun Ma, Qi-Kun Xue et al. (+1 more)
Two-dimensional superconductivity has become a major frontier in condensed matter physics. It holds the key to the mechanism of high-temperature
superconductors and offers an exceptional arena to stabilize emergent
quantum states enabled by enhanced electron correlations in reduced dimensionality. These states are frequently characterized by spatial modulations and intertwined with competing orders, calling for studies that combine real-space imaging with local spectroscopy. Scanning tunneling microscopy and spectroscopy meets this need by directly accessing local density of states with
lattice-scale resolution. In this review, we summarize recent advances of the study on several representative unconventional
superconductors using this technique, focusing on direct characterization of high-temperature superconducting planes, pair-density waves, and topological superconductivity in both artificial
heterostructures and intrinsic materials. We conclude by outlining current challenges and future directions motivated by the microscopic insights.
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All authors Qiang-Jun Cheng, Xu-Cun Ma, Qi-Kun Xue, Can-Li Song
Materials Science
Foundation-Model Surrogates Enable Data-Efficient Active Learning for Materials Discovery
Jeffrey Hu, Rongzhi Dong, Ying Feng et al. (+2 more)
Active learning (AL) has emerged as a powerful paradigm for accelerating materials discovery by iteratively steering experiments toward promising candidates, reducing the number of costly synthesis-and-characterization cycles needed to identify optimal materials. However, current AL relies predominantly on Gaussian Process (GP) and Random Forest (RF) surrogates, which suffer from complementary limitations: GP underfits complex composition-property landscapes due to rigid kernel assumptions, while RF produces unreliable heuristic uncertainty estimates in small-data regimes. This small-data challenge is pervasive in materials science, making reliable surrogate modeling extremely difficult with models trained from scratch on each new
dataset. Here we propose In-Context Active Learning (ICAL), which addresses this bottleneck by replacing conventional surrogates with TabPFN, a
transformer-based foundation model (FM) pre-trained on millions of synthetic regression tasks to meta-learn a universal prior over tabular data, upon which TabPFN performs principled
Bayesian inference in a single forward pass without
dataset-specific retraining, delivering strong small-data regression performance and well-calibrated predictive uncertainty (required for effective AL). We
benchmark ICAL against GP and RF across 10 materials
datasets and TabPFN wins on 8 out of 10
datasets, achieving a mean saving of 52% in extra evaluations relative to GP and 29.77% relative to RF. Cross-validation analysis confirms that TabPFN's advantage stems from superior uncertainty calibration, achieving the lowest Negative Log-Likelihood and Area Under the Sparsification Error curve among all surrogates. These results demonstrate that pre-trained FMs can serve as effective surrogates for active learning, enabling data-efficient discovery across diverse materials systems and small-data experimental sciences.
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All authors Jeffrey Hu, Rongzhi Dong, Ying Feng, Ming Hu, Jianjun Hu
Soft Condensed Matter
Polymer-Residue Accessibility Shapes Sequence Dependence of Critical Temperatures for Phase Separation
J. Pedro de Souza, Benjamin Sorkin, Amala Akkiraju et al. (+2 more)
Biological
polymers, such as intrinsically disordered
proteins, play a central role in cellular biology, including mediating phase separation and controlling activity of biological condensates. The physical properties and functions of biopolymers are determined by their residue sequence. Recently, significant computational and theoretical efforts have been devoted to characterizing the combinatorially complex sequence dependence of biopolymer phase diagrams. Here, we quantitatively show that monomer accessibility is central to determining the strength of pair interactions. We formulate an analytical perturbative approach, phenomenologically precluding two
polymers' centers of mass from overlapping within a correlation hole. This theory yields the correction to the strength of mean-field interactions in terms of a residue-accessibility parameter (RAP), which accounts for the limited availability of inner monomers to interactions. RAP rationalizes the variations in critical temperatures found in extensive Monte Carlo simulations for thousands of two-letter
polymer solutions of varying lengths and sequences. RAP may thus be effective for deciphering the
polymer-sequence dependence of phase diagrams given any
polymer length, set of monomer types, and
polymer mixtures.
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All authors J. Pedro de Souza, Benjamin Sorkin, Amala Akkiraju, Athanassios Z. Panagiotopoulos, Howard A. Stone