Materials Science
Room-temperature magnon-phonon transduction in high-damping Co/Pt structures
Gauravkumar Patel, Takuma Sato, Maximilian Frenzel et al. (+8 more)
Quantum communication and information processing strongly benefit from the coupling between different quasi-particles, offering complementary advantages. Magnetoelastic materials inherently allow for direct coupling between magnetization dynamics and quantized
lattice vibrations, called
phonons. Near the
ferromagnetic resonances,
phonons may thus trade energy and angular momentum with uniformly precessing magnetization, called
magnons, and enable transduction of information from
magnetic to phononic modes, thereby paving the way for long-range transport of
magnetic information without the need of
magnetic material. Here, we employ tailored
magnetic-nonmagnetic
heterostructures, which simultaneously act as cavities for standing shear waves, to bring selective
phonons and
magnons into resonance. These Co films with Pt seed layers show extended linewidth and reduced amplitude of the
phonon-resonant FMR lines, providing a hallmark of energy and angular momentum exchange. Complementarily, by theoretical modeling and ultra-fast coherent
phonon spectroscopy, we identify the responsible transverse acoustic
phonons as standing shear waves in the combined Co and Pt structure. We find a high
crystal quality in conjunction with a large magnetoelastic coupling constant as a prerequisite for efficient
magnon-
phonon coupling of this type. Such resonant enhancement of
magnon-
phonon coupling in CMOS-compatible material provides an ideal material platform for future
quantum transducers.
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All authors Gauravkumar Patel, Takuma Sato, Maximilian Frenzel, Prakriti P. Joshi, Ruslan Salikhov, Ievgeniia Korniienko, Dominik Legut, Olav Hellwig, Sebastian F. Maehrlein, Kilian Lenz, Jürgen Lindner
Materials Science
In situ synchrotron X-ray diffraction study of flash austenitization and process design insights in medium-Manganese steels for energy applications
Bowen Zou, Mathias Zapf, Thea Kannenberg et al. (+5 more)
Medium Mn steels (MMnSs) are promising candidates for energy-related infrastructure because their multiphase microstructures and austenite stability can be tailored to improve failure resistance under demanding service conditions. Flash austenitization (FA) provides a rapid route to form austenite while limiting prior austenite grain coarsening and substitutional solute homogenization, but the related short-time transformation kinetics remain insufficiently quantified. In the present work, the effects of FA temperature and initial microstructure on austenitization kinetics were investigated in an Fe-6Mn-1.5Si-1Cr-0.3Mo-0.05Nb-0.2C (wt.%) MMnS using dilatometry-integrated in situ synchrotron X-ray diffraction. Two initial microstructures produced by austenite reversion treatment (ART) were heated at 100 degrees C/s to 850 degrees C, 900 degrees C, or 950 degrees C and then held isothermally. Rapid heating alone is insufficient for full austenitization, even above the reference Ac3 temperature determined under slow heating. Full austenitization, defined by bcc fraction (f_alpha) <= 1 wt.%, requires short holding, decreasing from about 8 s at 850 degrees C to about 2 s at 950 degrees C. The final stage of austenitization is less sensitive to FA temperature than the early holding stage. The initial ART state mainly shifts the starting austenite fraction, whereas both states show comparable kinetic trends at higher FA temperatures.
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All authors Bowen Zou, Mathias Zapf, Thea Kannenberg, Daniel Schneider, Yixu Wang, Xiao Shen, Ulrich Prahl, Wenwen Song
Mesoscale and Nanoscale Physics
Determining Electron Beam Lateral Coherence in a Scanning Electron Microscope Using Electron Diffraction
Evelijn Akerboom, Fatemeh Kiani, Giulia Tagliabue et al. (+4 more)
We develop and characterize scanning transmission electron microscopy (STEM) capabilities within a scanning electron microscope (SEM) to investigate the effective lateral coherence of the electron beam (e-beam) in the specimen plane. Using single-crystalline Au flakes and a sample composed of a monolayer of
graphene, we obtain high-quality selected-area electron diffraction (SAED) maps and convergent-beam electron diffraction (CBED) patterns, validating the systems ability to probe crystallographic information at an acceleration voltage of 30 keV. Building on these capabilities, we implement a method, which is adapted from techniques traditionally used in transmission electron microscopy, to measure the degree of lateral coherence of the e-beam in the specimen plane of the SEM. By analyzing interference between electrons with two different wave vectors separated by 0.031 per angstrom, we extract a lower limit for the degree of lateral coherence over 5% of the e-beam diameter of approximately 60%. These coherence values are sufficient to enable
quantum-coherent electron-light-matter interaction experiments in the SEM.
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All authors Evelijn Akerboom, Fatemeh Kiani, Giulia Tagliabue, Wiebke Albrecht, Joanne Etheridge, F. Javier García de Abajo, Albert Polman
Statistical Mechanics · Cross-listed from quant-ph
Static features from mixing in short- and long-range Lindbladians: Markov property and correlations
Paul Rosa-Ruiz, Matteo Scandi, Ángela Capel et al. (+1 more)
The classification of mixed-state phases requires criteria beyond two-point correlation functions, such as the decay of the mutual information (MI) and the conditional mutual information (CMI), with the latter encapsulated in the notion of Markov length. Here we show how such static properties of the fixed point of a Lindbladian follow from natural dynamical features of its generators: rapid mixing and frustration-freeness. We focus on systems with long-range interactions, and prove (i) that local Lindbladians satisfying (global) rapid mixing and frustration-freeness have fixed-points whose CMI decays with the shielding distance, and (ii) that (local) rapid mixing together with primitivity and regularity implies global decay of MI. For long-range interactions decaying with a power law with rate $\alpha$, both quantities decay polynomially rather than exponentially, in contrast to the finite- and short-range regimes where exponential decay (a finite Markov length) is expected within a phase. We further show that Gibbs states of long-range, non-commuting
Hamiltonians satisfy a local Markov property at any temperatures, extending the recent results (Chen–Rouzé, 2025) for short-range systems to the long-range regime relevant to a variety of experimental platforms. As a numerical example, we study the long-range Ising model both with and without a transverse field. We find regimes in which the
polynomial decay of the CMI holds, in accordance with the bounds proven.
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All authors Paul Rosa-Ruiz, Matteo Scandi, Ángela Capel, Álvaro M. Alhambra
Soft Condensed Matter
Porosity Effects on Cyclic Gas Invasion and Trapping in Deformable Porous Media
Haiyi Zhong, Jieting Long, Xiangyu Ding et al. (+2 more)
Fluid transport in deformable porous media is central to many biophysical and geophysical processes. While extensive studies exist, how porosity governs fluid behaviour in deformable systems during cyclic injection remains elusive. Here, we investigate gas-
liquid multiphase flow in a quasi-2D Hele-Shaw
cell packed with soft hydrogel particles at different initial porosities. Alternative gas and water injection experiments, combined with high-resolution imaging and continuous pressure monitoring, are used to quantify gas dynamics and pressure
evolution. Results show that the gas entry pressure increases as porosity decreases, consistent with a Young-Laplace estimation based on effective pore-throat width. After entry, invasion shifts from cavity-dominated expansion in high porosity packings to localised pore invasion in low porosity packings, with a mixed cavity-fingering regime at intermediate porosity. Pressure fluctuations are linked to pore-scale gas escape and internal gas redistribution. Low porosity packings produce frequent small-amplitude pressure drops, whereas higher porosity packings produce more discrete pressure relaxations. Across cycles, the decreasing mean pressure suggests preferential-pathway reuse and reduced local capillary constraints. Residual gas saturation increases systematically with injection cycles and reaches higher terminal values as porosity decreases. Specific interfacial length increases as available pore space decreases and follows a power-law relationship with gas cluster size, with scaling exponent decreases as porosity decreases and cycling progresses. Together, these results demonstrate that gas trapping in deformable porous media depends on both initial packing structure and cyclically evolving gas-solid interactions. This study provides insights for interpreting porosity-dependent trapping and reinvasion during repeated gas injection.
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All authors Haiyi Zhong, Jieting Long, Xiangyu Ding, Zhongzheng Wang, Yixiang Gan
Strongly Correlated Electrons
Ferrimagnetic and Haldane-type phases in a mixed-spin $1$-$\tfrac{1}{2}$-$\tfrac{1}{2}$ quantum trimer chain
A. Felinto and R. R. Montenegro-Filho
Bipartite Lieb-Mattis ferrimagnetism and the
symmetry-protected Haldane phase are paradigmatic mechanisms in quasi-one-dimensional
quantum magnets. Both emerge, in distinct regimes, in a mixed-
spin $1$-$\tfrac{1}{2}$-$\tfrac{1}{2}$ Heisenberg trimer chain with
antiferromagnetic backbone exchange $J$ and a side
spin-$\tfrac{1}{2}$ coupled to each backbone
spin by an exchange $J_t$ of either sign. Using the density
matrix renormalization group, we compute magnetization curves and the
entanglement spectrum and
entropy. For $J_t>0$ a robust ferrimagnetic plateau forms at magnetization per unit
cell $m=1$, whose multiplet
entropy reflects how the conserved magnetization splits between the halves. For $J_t<0$ an $m=0$ plateau opens and grows with $|J_t|$, while the $m=1$ plateau closes. As $J_t\to-\infty$ the chain maps onto a
spin-$1$ Heisenberg chain with coupling $J/2$: the $m=0$ width $\Delta h\simeq 0.196$ matches half the Haldane gap. Exponentially localized
spin-$\tfrac{1}{2}$ edge states and the even-fold degeneracy of the
entanglement spectrum confirm the Haldane character of the $m=0$ phase.
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Strongly Correlated Electrons
Competing spin-1 and spin-2 regimes in a frustrated four-leg spin-1/2 ladder
D. S. Almeida and R. R. Montenegro-Filho
We investigate a frustrated four-leg
spin-$1/2$ ladder using density
matrix renormalization group calculations. The uniform system displays three regimes: short-range
antiferromagnetic legs, short-range
ferromagnetic legs, and an effective
spin-2 Heisenberg chain, separated by a crossover and a first-order transition. The
spin-2 regime is confirmed through its finite string order parameter, edge-localized excitations, and excellent agreement with a projected $S_r=2$ effective
Hamiltonian. Recasting the model as two frustrated two-leg ladders coupled by rung and diagonal interactions, we track how the trivial and Haldane phases of an isolated ladder evolve as interladder couplings are introduced. The resulting phase diagrams reveal crossover and first-order lines whose locations are captured by the
spin-2 projection and show how singlet- and triplet-dominated regimes reorganize when two ladders merge into a four-leg structure, clarifying the emergence of effective
spin-1 versus
spin-2 behavior.
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Statistical Mechanics
Nonextensive Statistical Signatures of the Bilaterian Transition in Proteome Length Distributions
Sertac Eroglu
Protein length distributions across the tree of life carry a quantitative signature of organismal complexity. Nonextensive statistical mechanics, through the Tsallis generalized
entropy formalism, provides a natural framework for describing complex systems characterized by long-range correlations, scale invariance, and hierarchical organization – features that classical Boltzmann-Gibbs statistics cannot accommodate. In this work, the complementary cumulative distribution function (CCDF) of
protein lengths is analyzed within this framework for the reference proteomes of 22 fully sequenced organisms spanning the domains Archaea, Bacteria, and Eukarya, with deliberate sampling across the animal transition zone from sponges and cnidarians to higher bilaterians. Maximum likelihood (MLE) fitting of truncated discrete q-exponential distributions, with bootstrap 95% confidence intervals (CIs) reveals that the entropic index q resolves into three statistically distinct regimes: superextensive (q < 1) for prokaryotes, unicellular and non-animal multicellular eukaryotes, and basal animals; a boundary regime (CI on spanning unity) for the two cnidarians studied and the basal bilaterian C. teleta; and subextensive (q > 1) for all higher bilaterians, with q increasing monotonically across the four deuterostomes sampled from S. purpuratus (1.033) to H. sapiens (1.147). The q-exponential outperforms the ordinary exponential distribution across all 22 proteomes and becomes progressively more competitive against alternative two-parameter distributions as proteome complexity increases. These results identify the Tsallis entropic index as a continuous, physically interpretable indicator of proteome organizational complexity and extend the applicability of nonextensive statistical mechanics to proteomic systems.
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Strongly Correlated Electrons
Comment on "Altermagnetic and Dipolar Spitting of Magnons in FeF_2" arXiv:2601.04303
S. W. Lovesey
Conclusions by Sears et al. (arXiv: 2601.04303) about dispersions of
magnons in rutile FeF_2 are unsound because compulsory
lattice vibrations are omitted in the analysis of their
neutron scattering spectra. Hybridized
magnon-
phonon modes in magnetically ordered FeF_2 were observed and successfully analysed half a century ago.
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Statistical Mechanics
A Finite Element Method for Fluctuating Navier–Stokes Equations
Dimitrios Gourzoulidis, Mirko Gallo, Soumaya Elkantassi et al. (+2 more)
We introduce a finite-element framework for simulating thermal fluctuations in compressible fluids governed by the fluctuating Navier-Stokes equations. The method is designed to preserve the fundamental fluctuation-dissipation balance at the discrete level. This is achieved by defining the
stochastic forcing term in the weak formulation, ensuring its covariance is proportional to the discrete viscous dissipation operator. A nodal quadrature rule is employed to eliminate unphysical mesh-scale correlations. The time integration is performed using the Crank-Nicolson scheme to maintain numerical stability and accuracy. The proposed approach is numerically validated in one, two, and three spatial dimensions, demonstrating its capability to correctly capture
equilibrium fluctuation statistics across various discretisation parameters.
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All authors Dimitrios Gourzoulidis, Mirko Gallo, Soumaya Elkantassi, Toby Kay, Serafim Kalliadasis
Mesoscale and Nanoscale Physics
Hidden valley dynamics behind vanishing circular polarization in moiré excitons
Yuto Urano, Lata Chouhan, Nurul Fariha Ahmad et al. (+4 more)
Optically addressable valley degrees of freedom in transition-metal dichalcogenide
heterostructures provide a powerful platform for valleytronic and
quantum-optical functionalities. In moiré superlattices, interlayer
excitons inherit valley-contrasting optical selection rules while acquiring long lifetimes, electric dipoles, and site-dependent optical responses. However, because conventional measurements typically probe time-integrated valley polarization, the dynamical origin of vanishing polarization has remained elusive. Here, we show that a nearly zero steady-state valley polarization in electrically tunable moiré
excitons does not necessarily indicate fast valley relaxation. Helicity-resolved time-resolved photoluminescence reveals a temporal crossing between co- and cross-circularly polarized emission, indicating that helicity-opposite dynamical components coexist and compensate after time integration. A minimal two-channel model, representing A-like and B-like moiré emission channels with opposite optical selection rules and distinct effective decay/depolarization rates, reproduces the observed helicity crossing without invoking a single rapid valley relaxation process. Furthermore, two-dimensional gate-field maps show that the crossing time evolves systematically with electrostatic tuning, demonstrating that the hidden valley dynamics are electrically controllable. These results show that time-integrated circular polarization can give a false-negative indication of valley polarization in multichannel valley emitters.
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All authors Yuto Urano, Lata Chouhan, Nurul Fariha Ahmad, Kenji Watanabe, Takashi Taniguchi, Daichi Kozawa, Ryo Kitaura
Disordered Systems and Neural Networks · Cross-listed from q-bio.NC
Cell-type-specific synaptic motifs generate coupled mean-variability dynamics in recurrent neural networks
Meiyi Zhang, Jinjian Yu, Louis Tao et al. (+1 more)
Synaptic-resolution network connectomics has revealed that
brain circuits feature fine-scale structural connectivity, such as pairs of correlated synaptic couplings known as second-order motifs. Large-scale recordings of neuronal activity in networks containing nonlinear
neurons reveal macroscopic heterogeneous population dynamics throughout the
brain. These findings rekindle the inquiry into this intriguing question: Can microscale synaptic structures contribute to macroscopic heterogeneous dynamics and computations in ways that canonical
brain circuit models cannot? To answer this question, we construct random RNNs with various
cell types, nonlinear non-negative neural responses, and arbitrary marginal and second-order correlated synaptic statistics. We derive low-rank mean-field equations for \(P\)-population networks in which the pre- and postsynaptic neuronal population identities determine the synaptic and motif strengths. Our framework requires \(2P\) latent dynamic variables with \(P\) variables describing mean population activity and \(P\) variables capturing within-population variability. Theoretical and numerical results demonstrate that chain motifs induce correlations in synaptic variability, coupling within-population variability to population mean dynamics through nonlinear gain. We use this framework to construct network models constrained by experimentally observed motif statistics that reproduce key population activity patterns in the mouse primary visual cortex. By explicitly linking synaptic organization to coupled mean-variability dynamics, our results provide a testable framework for studying the relationship between fine-scale connectivity, heterogeneous dynamics, and task-related responses.
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All authors Meiyi Zhang, Jinjian Yu, Louis Tao, Yuxiu Shao
Mesoscale and Nanoscale Physics
Open Nanoacoustic Resonators Based on SrTiO$_3$/YBa$_2$Cu$_3$O$_{7-x}$ Superlattices
S. Sandeep, O. Colmegna, S. Carreira et al. (+4 more)
We report the design and experimental demonstration of an open nanophononic cavity based on a hybrid
oxide superlattice composed of SrTiO$_3$ (STO) and YBa$_2$Cu$_3$O$_{7-x}$ (YBCO), combined with a metallic Ni transducer for coherent
phonon generation. The STO/YBCO periodic stack acts as an acoustic distributed Bragg reflector supporting confined longitudinal acoustic
phonons in the sub-THz regime, while the Ni layer enables efficient ultrafast optical excitation and detection by time-domain Brillouin scattering. Transient reflectivity measurements reveal confined acoustic dynamics and a well-defined cavity resonance, in agreement with transfer-
matrix calculations of acoustic reflectivity and mode profiles. These results demonstrate
phonon confinement in multifunctional
oxide heterostructures and establish complex
oxide superlattices as a platform for hybrid nano-acoustic resonators and ultrafast
phonon control of correlated electronic phases.
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All authors S. Sandeep, O. Colmegna, S. Carreira, L. M. Vicente-Arche, L. B. Steren, J. Briatico, N. D. Lanzillotti-Kimura
Strongly Correlated Electrons
Metamagnetism in UTe2: the roles of itinerancy and localization
Theodore I. Weinberger, Daniel Shaffer, Zheyu Wu et al. (+12 more)
The metamagnetic transition in UTe$_2$ plays a key role in stabilizing two enigmatic field-induced superconducting phases. One of these phases (SC2) is truncated by the transition, lying directly below it, while the other (SC3) sits predominantly above it and appears to be stabilized because of it. While numerous pulsed field studies have examined this transition, comparatively few steady field experiments have investigated it. Here we report a suite of measurements of metamgnetism in UTe$_2$, at ambient pressure by torque magnetometry and extraction magnetometry techniques, and of the magnetoconductance under pressure. Our steady field measurements resolve a complex sub-structure within the transition, with separate features that possess different temperature evolutions, pointing to distinct contributions from itinerant and localized moments. The itinerant contribution might relate to a possible
spin-density wave state. We theoretically model the
evolution of Kondo and RKKY interactions and propose that the SC2 state is stabilized under pressure due to the collapse of
magnetic anisotropy, leading to an enhancement of longitudinal
spin fluctuations along the hard $b$ axis, which are pair-forming in the $p$-wave channel.
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All authors Theodore I. Weinberger, Daniel Shaffer, Zheyu Wu, Dmitry V. Chichinadze, Jinxu Pu, Gang Li, Rui Zhou, Yurii Skourski, Dave Graf, Andrej Cabala, Vladimir Sechovsky, Michal Valiska, Michal P. Kwasigroch, F. Malte Grosche, Alexander G. Eaton
Materials Science
Symmetry-Selective Strain Control of Spin-Momentum Locking and Spin Transport in Two-Dimensional Pentagonal Altermagnets
ShuaiYu Wang, Sheng Chen, Xiao-Ping Li et al. (+1 more)
Altermagnets are compensated magnets featuring momentum-dependent nonrelativistic
spin splitting generated by nontrivial operations connecting opposite-
spin sublattices. A direct
symmetry-based route to control this
spin splitting is to modify the real-space operations that define the altermagnetic
spin-momentum locking (SML). Here, we develop a strain-resolved
symmetry framework for two-dimensional pentagonal altermagnets, classifying whether uniaxial and shear strain tensors preserve, reconstruct, or eliminate the SML. Using the above criterion combined with first-principles screening, we identify 94 stable altermagnetic candidates from 3330 materials. These candidates cover all type-III
spin Laue groups of orthorhombic
lattices and are classified into three strain-response types: Type-I preserves the SML; Type-II reconstructs the SML through partial
symmetry breaking while retaining essential altermagnetic features; and Type-III destroys the altermagnetic SML. Representative materials further demonstrate this classification: ferroelastic $\alpha$-CoS$_2$ exhibits ferroelastically switchable SML and reverses the sign of the off-diagonal
spin conductivity; shear-strained \(\alpha\)-CoP\(_2\) undergoes a \(g\)- to \(d\)-wave reconstruction of the SML, activating off-diagonal
spin conductivity; and uniaxially strained FeSSe realizes strain-selected
spin-valley transport. This work provides theoretical and material guidance for strain-controlled transport in two-dimensional orthorhombic altermagnets.
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All authors ShuaiYu Wang, Sheng Chen, Xiao-Ping Li, Lei Wang
Materials Science
Unlocking Cryogenic Energy Storage by Constructing Dipole Glass with Unit-cell-level Polar Disorder
Yangyang Si, Denan Li, Yijie Li et al. (+21 more)
Cryogenic energy storage is vital for frontier technologies including deep-space exploration and
quantum computing, yet conventional electrochemical energy systems fail below ~230 K due to frozen ion migration. While relaxor-based dielectric capacitors provide high efficiency at room temperature, the intrinsic freezing/growth of polar nanodomains at extended cryogenic regime limits their applications with deteriorated hysteresis losses. Here, we realize superior cryogenic energy-storage performance by designing unit-
cell-level disordered dipole-glass state in Pb0.6Sr0.4ZrO3 thin films with composition near antiferroelectric-paraelectric phase boundary. The antiferroelectric-derived dipole-glass introduces enhanced unit-
cell-level complexity of dipole interaction that suppresses long-range ferroelectric order. This enables ultralow-hysteresis operation (efficiency > 88%) down to 4 K, delivering record-high energy density (211 J/cm^3) at 9 MV/cm, stability over 10^8 charge/discharge cycles and microsecond-scale charge/discharge capability. This work establishes a dipole-glass paradigm for cryogenic dielectric capacitors, opening a new avenue to highly-efficient energy-storage systems with broad applications in frontier nanoelectronics.
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All authors Yangyang Si, Denan Li, Yijie Li, Changsheng Chen, Jingxuan Li, Chao Zhou, Hao Xiong, Tianfu Zhang, Wenjin Liao, Zhongqi Ren, Huaicheng Yuan, Dong Li, Jing-Kai Qin, Cheng-Yan Xu, Ye Zhu, Yunlong Tang, Sujit Das, Jieun Kim, Junling Wang, Hao Pan, Fei Li, Zhen Chen, Shi Liu, Zuhuang Chen
Disordered Systems and Neural Networks
A stochastic model of a nuclear reactor with directed percolation. Overjump and maximum power
V. V. Ryazanov
A
stochastic risk model is applied to simulating the behavior of a
nuclear reactor in a situation where the
neutron chain length is described by a distribution with heavy "tails," such as the Pareto distribution. Probabilities of a fluctuation exceeding a critical threshold are obtained, and risk bounds for power-law distributions of jumps are estimated. Functionals of the reactor power maximum, the instant of first reaching the maximum, and the distribution of the overjump magnitude are considered. A relationship between the shape parameter and the physical constants of reactors is obtained, as well as the relationship with the noise spectrum and physical constants. The finite dimensions of a real reactor are taken into account. The autocorrelation function of the truncated Lévy process and its relationship with the frequency filters of the
neutron flux monitoring equipment are considered.
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Statistical Mechanics
Quantum enhancement of information-mediated energy transfer
Shotaro Oki, Yuki Kadono, Kaito Tojo et al. (+2 more)
Thermodynamics of information identifies information flow as a thermodynamic resource, but whether
quantum coherence and collective coupling can enhance it at low
entropy-production cost remains unresolved. We address this question for interacting open
quantum systems by deriving a thermodynamic uncertainty relation that bounds information flow in terms of
entropy production in nonequilibrium steady states. We construct a
quantum engine in which N-fold degenerate ground and excited states are collectively coupled to heat baths. Collective jumps enhance heat currents and information flow linearly with N, while
entropy production remains independent of N, realizing a high-power, low-dissipation autonomous
quantum Maxwell's demon that leverages collectively enhanced information flow to pump heat against a temperature gradient. Beyond steady states, collective interactions amplify the
unitary component of
quantum information flow, yielding a quadratic enhancement of the free-energy charging power of
quantum batteries. Our results reveal scalable advantages of
quantum coherence and collective effects in
quantum engines.
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All authors Shotaro Oki, Yuki Kadono, Kaito Tojo, Takahiro Sagawa, Ken Funo
Materials Science
Single-Crystalline Al/Ge Heterostructure with an Atomically Sharp Commensurate Interface
Jian-Huan Wang, Ding-Ming Huang, Han Gao et al. (+3 more)
A key challenge in developing Al/Ge
heterostructures for
quantum applications is Al-Ge interdiffusion. This process is facilitated by grain boundaries in polycrystalline films, which degrades interface quality and impairs device performance and reliability. Here, we present epitaxial growth of single-crystalline Al(111) on Ge(111) by molecular beam epitaxy, achieving an atomically flat and sharp interface. At the interface, a commensurate 7-Al-
lattice/5-Ge-
lattice epitaxial relationship is observed, which dramatically reduces the intrinsic
lattice mismatch from 28.4% to about 0.1%. Interestingly, this well-ordered interface does not form below a critical thickness of 0.3 nm. Instead, Al initially nucleates as random clusters, which then transform into two-dimensional (2D) islands and, as Al deposition further increases, eventually develop into a continuous film. By optimizing the growth parameters, we have achieved an ultra-flat Al film with a surface root-mean-square roughness of about 0.16 nm and an ultra-thin continuous film with thickness of only 2 nm. These epitaxially grown Al-Ge
heterostructures, with their atomically flat surfaces and sharp interfaces, provide a promising platform for studying topological
quantum states.
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All authors Jian-Huan Wang, Ding-Ming Huang, Han Gao, Yuan Yao, H. Q. Xu, Jian-Jun Zhang
Statistical Mechanics
Rare Events Govern Defect Formation under Weak Symmetry Breaking
Jiang Liu, Peng Yang and Matteo Baggioli
Crossing a continuous phase transition out of
equilibrium typically generates topological defects whose density obeys a universal power-law scaling predicted by the Kibble-Zurek mechanism. Recent numerical studies have revealed systematic deviations from this scaling in the presence of weak explicit
symmetry breaking, manifested as an additional exponential suppression of defect formation. However, the origin of this correction and a general theoretical framework to describe it have remained elusive. Here, using large-deviation theory, we show that defect formation under weak
symmetry breaking is controlled by rare fluctuations that drive local regions into the disfavored
symmetry-broken state. This mechanism yields a closed-form expression for the defect density in arbitrary dimensions, valid in the weak-field and weak-noise limits. These theoretical predictions are verified through direct simulations of
stochastic Ginzburg-Landau models in one and two spatial dimensions.
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Mesoscale and Nanoscale Physics
Theory of Electron Spin Resonance Scanning Tunneling Microscopy: The First Decade
Saba Taherpour, Denis Janković, Jose Reina-Galvez et al. (+2 more)
Electron
spin resonance in scanning tunneling microscopy enabled the study of electronic transitions of
magnetic impurities on surfaces at the atomic scale. This ESR-STM technique allows to spectroscopically probe and coherently manipulate
spins using an all-electrical method without oscillating external
magnetic driving fields. Here, we aim to review recent advancements in ESR-STM. We will discuss possible fundamental mechanisms by which the electric field drives
spin resonance based on Heisenberg exchange, Kondo scattering, and Anderson
impurity models. We validate theoretical predictions against experimental observations, to understand how electronic correlations,
spin exchange, and many-body effects manifest in ESR-STM signals. After reviewing coherent
spin control in the STM junction, we discuss potential applications of the ESR-STM method for coherent multi-
spin control which enables multiple-
qubit operations. Finally, we address recent developments in coupled electron-
nuclear spin systems, including hyperfine-resolved ESR spectroscopy, and the driving and polarization of
nuclear spins in ESR-STM.
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All authors Saba Taherpour, Denis Janković, Jose Reina-Galvez, Hoang-Anh Le, Christoph Wolf
Quantum Gases
Universality in strongly interacting bosonic clusters
L. Madeira, F. Pederiva and U. van Kolck
We develop an effective field theory (EFT) for strongly interacting bosonic clusters, using $^4$He as a paradigmatic example of universality in systems with large scattering length. At leading order (LO), two- and three-body zero-range interactions are entirely determined by the dimer and trimer ground-state energies. We show that ground-state energies for up to $N=15$ particles converge to cutoff-independent limits with extrapolation coefficients of natural size. At next-to-leading order (NLO), corrections stemming from the two-body interaction range and a four-body force, calibrated to the tetramer ground-state energy, reduce cutoff sensitivity. Close agreement with results from a realistic potential is found at LO and improved at NLO, demonstrating systematic convergence with few parameters at each order. The resulting EFT is directly applicable to larger clusters and bulk helium.
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Mesoscale and Nanoscale Physics
A real-space exceptional ring mediates an eigenframe-charge transition in a non-Hermitian skyrmion
Kejun Liu
The integer topological charge of a skyrmion is the standard example of topological protection. We ask what happens to that protection when the local generator is made non-Hermitian by polarization-selective gain or loss. The texture charge of a smoothly evolving state remains homotopy-protected under the usual fixed-boundary condition: after projective normalization, the gain/loss contribution has the Gilbert relaxation form on the target sphere. The spectral charges of the local generator behave differently. Its biorthogonal eigenframe charge is quantized while the texture avoids exceptional points. At linewidth matching, the skyrmion equator becomes a real-space exceptional ring on which the biorthogonal Bloch field diverges, and the eigenframe class jumps from +1 to 0 in a parameter-driven spectral transition. The closed contour relies on constant splitting along the equator, or an equivalent design constraint; a partial or amplitude-anisotropic realization instead leaves isolated real-space exceptional points. We use an operational Jones parametrization of an isolated polarization doublet and give a Stokes-
tomography reconstruction of the left-right frame. The result identifies a spatially resolved exceptional contour that mediates an integer transition of a real-space eigenframe charge.
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Disordered Systems and Neural Networks
Mingpu Jiang and Jianhui Zhou
The
quantum geometric tensor is a fundamental property of
quantum states, with broad applications in condensed matter physics, topological phases, and
quantum phase transitions. The
eigenvalues characterize the scale, anisotropy, and effective rank of random
quantum geometry, going beyond scalar quantities such as the trace. Here we study the
eigenvalue statistics of the
quantum geometric tensor in finite-dimensional parameter-dependent random
Hamiltonians. We obtain exact analytical results for the first two nontrivial cases, $N=2$ and $N=3$, with $N=3$ already showing genuine shape fluctuations. We further propose a finite-$N$, arbitrary-$D$ description of QGT
eigenvalue statistics and verify it by numerical simulations. Our results provide exact
benchmarks and a practical framework for random
quantum geometry in finite-dimensional disordered and chaotic systems.
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Mesoscale and Nanoscale Physics
Non-Newtonian two-dimensional electron fluid in magnetic field
P. S. Alekseev and M. A. Semina
We develop a theory of the non-Newtonian regime of non-linear hydrodynamic magnetotransport of a two-dimensional (2D) viscous electron fluid controlled by the local Joule heating. In this mechanism, the electron shear viscosity in
magnetic field becomes a non-monotonic function of the gradient of the hydrodynamic velocity due to the flow-induced increase of the electron temperature. We derive and solve the corresponding non-linear hydrodynamic equations for a velocity profile in a Poiseuille-like flow geometry. We demonstrate that the calculated magnetoresistance of such flow well explains the differential magnetoresistance observed for 2D electrons in various samples of ultra-high-quality GaAs
quantum wells at high currents. We conclude that the non-linear regime of 2D electron fluid flows is such systems is realized via formation of a 2D non-Newtonian electron fluid, related to non-linearity in viscosity, but not via convective “kinematic-induced” effects, as it takes place in ordinary uncharged fluids.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Industry-ready spin-photon interfaces for hybrid photonic quantum computing
Hêlio Huet, Hubert Lam, Thibaut Pollet et al. (+45 more)
Hybrid photonic
quantum computers, combining stationary matter
qubits and flying photonic
qubits, offer an intrinsically networked and resource-efficient route to large-scale, error-corrected
quantum computation. Their core components are cavity-coupled matter
qubits that act as light–matter interfaces, enabling: high-efficiency on-demand single-
photon generation, stable near-unity
photon indistinguishability and
spin–multi-
photon entanglement.
Semiconductor quantum dots in microcavities are a leading platform for realizing such devices. Yet reaching the performance, reproducibility and
spin-coherence thresholds for large-scale error correction remains a major challenge requiring industrial fabrication and control. Here we report thousands of monolithic
semiconductor quantum-dot devices fabricated using a III–V pilot production-line process compatible with large-scale deployment. Systematic control of source parameters yields state-of-the-art efficiency and supports a path to optical losses below fault-tolerance thresholds. Using field-quadrature state reconstruction as a stringent joint test of efficiency and indistinguishability, we observe near-unity
photon quantum purity stable over tens of minutes and a record single-
photon Wigner-function negativity. We further demonstrate seven-partite
spin–multi-
photon entanglement and
spin coherence extendable to microsecond timescales in the low-
magnetic-field regime. Finally,
photons from distant sources are as indistinguishable as
photons emitted successively by a single source. These results establish foundry-compatible III–V
quantum dots as a scalable platform for hybrid photonic
quantum computing.
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All authors Hêlio Huet, Hubert Lam, Thibaut Pollet, Petr Steindl, Alice Bernard, Albert Adiyatullin, Petr Stepanov, William Hease, Victor Guilloux, Nico Margaria, Joris Verstraten, Raksha Singla, Samuel T. Mister, Anton Pishchagin, Lara Couronné, Samuel Huber, David Sebastian, Duc Duy Tran, Thi Hao Nhi Nguyen, Thi Phuong Do, Joseph Sulpizio, Yann Portella, Kiarn T. Laverick, Thinhinane Bennour, Tomas Alexandre De Sousa, Davide Stefani, Mathias Pont, Maxime Descampeaux, Bianca Scaparra, Martin A. Jacobsen, Klaus D. Jöns, Rinaldo Trotta, Aristide Lemaître, Martina Morassi, Olivier Krebs, Loïc Lanco, Niels Gregersen, Alexia Auffèves, Maria Maffei, Shane Mansfield, Jean Senellart, Thomas Volz, Viviana Villafañe, Stephen C. Wein, Dario A. Fioretto, Sebastien Boissier, Thi Huong Au, Pascale Senellart
Mesoscale and Nanoscale Physics
Confined exciton polaron in MoS$_2$ on twisted-hBN
Garima Gupta, Mayank Chhaperwal, Pankaj Kumar et al. (+5 more)
The simple electrostatic picture of a trion is that of an excess charge inducing an
exciton polarization and binding closer (farther) to the hole (electron) side of it. Trion formation can be forbidden when such spontaneous rearrangement of charges is not allowed by the application of external perturbation, such as electric field. Here we test this hypothesis experimentally using a non-monotonic electric field. We realize this scenario by imprinting the ferroelectric domains at the AA-stacked twisted-hBN (t-hBN) interface onto a monolayer of MoS2 placed over it. The spatially varying in-plane electric field around the domain wall serves the dual purpose of (a) confining and polarizing the 2D
exciton in the domain wall, and (b) depleting the free charge carriers from the domain wall. We observe a large quantized
exciton splitting confirming strong
exciton confinement in the domain wall. Forced by the confining potential, the electron side of the polarized
exciton lies closer to the domain with accumulated free electrons, which should ideally prevent any trion formation. Contrary to the laid hypothesis, we observe signatures of quantized charged
exciton emission, with an inter-level splitting that mimics the level-splitting of the quantized
excitons. This paradox is explained using the many-body picture of
exciton polaron, where a conduction band hole attractively binds the polarized
exciton and the electron
Fermi sea. The results provide a definitive way to unambiguously discern
exciton polaron from trion.
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All authors Garima Gupta, Mayank Chhaperwal, Pankaj Kumar, Pushkar Dasika, Kenji Watanabe, Takashi Taniguchi, Archana Raja, Kausik Majumdar
Quantum Gases
Collision and coalescence dynamics of bosonic quantum Hall droplets
Xinyi Liu, Zhendong Li, Yuwen Zhou et al. (+5 more)
Recently bosonic
quantum Hall droplets have been observed in rapidly rotating two-dimensional Bose-Einstein condensates (BECs), which exhibit robust dynamical stability. Inspired by this, we systematically investigate the collision and coalescence dynamics of these droplets within the Gross-Pitaevskii framework. For two-droplet collisions, we find two distinct collision outcomes, namely merging and separation, that are controlled by the initial relative velocity. The critical velocity exhibits a universal scaling law with the interaction and the particle number as $v_c \propto (gN)^{1/4}$, which can be interpreted from a simplified analytical model, revealing the essential role of the collision time. It differs fundamentally from the mechanism governing the conventional Lee-Huang-Yang stabilized
quantum droplets. Furthermore, while the collision can change the shape of the droplet significantly, the center of mass trajectory remains nearly unaffected, owing to the conservation of angular momentum. For overlapping stationary droplets,
vortex arrays can emerge through Kelvin-Helmholtz instability driven by phase-induced shear flow. Although two droplets may merge into a larger one, extended states cannot be constructed from multiple overlapping droplets. Instead, the system dynamically reorganizes into new isolated droplets, revealing the localized property in the bulk region. Our results reveal the unique nonequilibrium dynamics of
quantum Hall droplets and suggest new pathways for manipulating strongly correlated rotating
quantum fluids.
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All authors Xinyi Liu, Zhendong Li, Yuwen Zhou, Siying Li, Haoran Xu, Zihe Liu, Rongzhen Jiao, Mingyuan Sun
Materials Science
Three-dimensional visualization of threading dislocation in GaN by polarized-light microscopy
Yukari Ishikawa, Kisara Matsumoto, Kazuki Ohnishi et al. (+1 more)
We demonstrate high-throughput three-dimensional imaging of threading dislocations in ammonothermal GaN wafers using polarized-light microscopy with collimated LED illumination. Threading dislocations exhibited focal-depth-dependent in-plane shifts, enabling visualization of their three-dimensional inclination behavior over large areas. Synchrotron radiation X-ray topography indicated that dislocations with identical in-plane Burgers vector components tended to exhibit similar trace geometries and inclination directions. The threading dislocations were found to be tilted by approximately 3.3{\deg} from the c-axis in directions perpendicular to their Burgers vectors, indicating climb-mediated motion associated with strain relaxation during
crystal growth. These results demonstrate a simple nondestructive approach for large-area three-dimensional characterization of dislocations in GaN wafers.
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All authors Yukari Ishikawa, Kisara Matsumoto, Kazuki Ohnishi, Yongzhao Yao
Materials Science · Cross-listed from quant-ph
Fault tolerant computation of the static structure factor and finite size effects
Rishabh Bhardwaj, Alexander Reed Muñoz, Travis E. Jones et al. (+1 more)
Fault-tolerant
quantum algorithms offer a promising pathway for estimating the ground-state energies of periodic materials that are beyond the practical reach of classical electronic-structure methods. A remaining challenge is finite-size mitigation:
quantum algorithms evaluate a finite supercell or finite Brillouin-zone mesh, while materials properties are defined in the thermodynamic limit. In this work we develop a
quantum post-processing strategy for the leading two-body finite-size correction. After one-body shell effects are reduced by twist averaging, the dominant residual error is controlled by long-wavelength density fluctuations, which are encoded in the small-momentum static structure factor $S(q)$. We formulate the corresponding operator in a Bloch-orbital basis, construct its block encoding through the density operator, and estimate its ground-state expectation value using an amplified Hadamard test. We also introduce adaptive global and local binary search procedures for identifying the infrared fitting window used to reconstruct the two-body finite size error correction. The resulting cost remains subleading relative to the main ground-state energy estimation routine: the structure-factor correction has leading $\tilde{O}(N_bN_k)^3$ dependence on the Bloch-orbital basis size, avoids the large plane-wave prefactor of full
Hamiltonian simulation, and requires only $\tilde{O}(N_bN_k)$ logical
qubits. This provides a fault-tolerant alternative to down-sampling, replacing repeated energy calculations on larger
cells with targeted measurements of the infrared density correlations that control the finite-size effects.
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All authors Rishabh Bhardwaj, Alexander Reed Muñoz, Travis E. Jones, John Golden