Materials Science
Effect of Al-Zn alloy wafer grain boundary diffusion on the magnetism and microstructure of sintered NdFeB magnets
Xi Liu, Wenxi Fang and Ken Perlin
This study investigates Al-Zn grain boundary
diffusion (GBD) treatment on sintered Nd-Fe-B magnets using $Al_{80}Zn_{20}$
alloy sheets as the
diffusion source. The
alloy sheets were placed at both ends of cylindrical samples and
diffusion-annealed at 900$^\circ$C and 700$^\circ$C for 7 hours under
vacuum ($\leq5\times10^{-3}$ Pa), followed by tempering at 500$^\circ$C for 2 hours.
Magnetic measurements show that coercivity increases from 951.5kA/m in the untreated sample to 1158.2kA/m at 900$^\circ$C (a gain of 206.7kA/m, 21.7%) and to 1039.6kA/m at 700$^\circ$C (a gain of 88.1kA/m, 9.3%), while remanence declines modestly from 1282mT to 1256mT after the high-temperature treatment. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometer (XRD) analyses reveal that the 900$^\circ$C treatment produces a thinner, more continuous grain boundary phase and a distinct core-shell structure around the main-phase grains. EDS mapping shows that Al preferentially enriches the shell region of the $Nd_2Fe_{14}B$ grains, while Zn predominantly resides in the grain boundary phase, where it lowers the melting point of the intergranular phase and improves its fluidity. XRD shows no detectable secondary phases, while the combined XRD, EDS results, and
lattice expansion are consistent with possible limited Al incorporation into the main-phase
lattice. Verified by computational analysis, the coercivity enhancement is attributed to three synergistic factors: improved grain boundary decoupling, the formation of a high-anisotropy shell layer that strengthens domain-wall pinning, and the smoothing of grain edges to suppress reverse-domain nucleation.
Read the full abstract ▾
Strongly Correlated Electrons
Quasi-Two-Dimensional Quantum Antiferromagnetism in the Distorted Honeycomb Compound KCuIn(PO4)2
S. Gayen, S. S. Ali, V. K. Singh et al. (+2 more)
We investigate the electronic structure and
magnetic properties of the distorted honeycomb
lattice compound KCuInP2O8 through a combination of experimental measurements, first principles calculations and
quantum monte carlo simulations. Density functional theory calculations within the GGA+U framework establishes KCuInP2O8 as an indirect gap
insulator with Cu2+ local moments and finite magnetocrystalline anisotropy arising from
spin orbit coupling. A microscopic evaluation of
magnetic exchange interactions using the
magnetic force
theorem reveals a pronounced hierarchy of couplings, with the next nearest neighbor interaction dominating over the nearest neighbor exchange, while interlayer couplings remain negligible. This exchange hierarchy naturally maps the system onto weakly coupled
antiferromagnetic spin chains embedded in a distorted honeycomb
lattice. Motivated by the ab initio estimated exchange interactions, we construct an effective
spin half
Hamiltonian and investigate its
magnetic response using large scale
quantum Monte Carlo simulations. The calculated temperature dependent susceptibility and field dependent magnetization quantitatively reproduce the experimental behavior and capture key signatures of low dimensional
quantum magnetism, including a broad susceptibility maximum and a field induced saturation at low temperatures. Our results establish KCuInP2O8 as a quasi-two-dimensional
quantum antiferromagnet composed of coupled
spin chains, providing a consistent theoretical framework that links electronic structure, exchange interactions, and collective
magnetic behavior.
Read the full abstract ▾
All authors S. Gayen, S. S. Ali, V. K. Singh, B. Koteswararao, S. K. Panda
Materials Science
Property-Guided Diffusion for Inverse Design of Crystalline Materials
Sourav Mal, Subhankar Mishra and Prasenjit Sen
Diffusion-based generative models with property guidance have emerged as a promising paradigm for inverse materials design by enabling the generation of crystalline materials with user-specified target properties. However, despite recent advances, the effectiveness of property guidance, its influence on crystallographic
symmetry, and the physical viability of generated materials remain poorly understood. To address these questions, we develop a property-guided framework based on the lightweight
diffusion model DiffCrysGen using parameter-efficient adapter fine-tuning and classifier-free guidance (CFG). The resulting framework enables efficient multi-property
crystal generation while preserving the knowledge learned during unconditional pre-training. Using formation energy together with saturation magnetization and Vickers hardness as representative inverse-design tasks, we systematically investigate the influence of CFG across a broad range of guidance strengths. Increasing the guidance scale progressively steers the generated property distributions toward the prescribed targets while reducing the fraction of lowest-
symmetry ($P1$) structures and increasing the proportion of higher-
symmetry structures. To evaluate physical viability, generated structures are geometrically prescreened and subsequently validated using a machine-learning interatomic potential (MLIP)-based workflow comprising structural relaxation and thermodynamic, dynamical, and property-specific analyses. The framework identifies thermodynamically and dynamically stable
magnetic and mechanically hard materials with overall success rates of 12.3% and 3.9%, respectively. These results establish property-guided DiffCrysGen as an efficient framework for inverse materials design while providing new insights into the role of classifier-free guidance in
crystal generation.
Read the full abstract ▾
Materials Science · Cross-listed from physics.comp-ph
Learning Lattice Parameters from Powder X-Ray Diffraction Data Using Invariants
Elyssa Hofgard, Kyucheol Min, Nofit Segal et al. (+8 more)
We present a machine learning (ML) method to determine unit
cell parameters from powder X-Ray diffraction (XRD) data using a novel invariant
lattice representation. In ML, the data representation used can have a substantial impact on the prediction quality. Previous approaches have directly predicted
lattice parameters ($a,b,c,\alpha,\beta,\gamma$) from XRD inputs. However, these parameters depend strongly on the unit
cell reduction or convention used. In this work, we construct an invariant representation of the reciprocal
lattice that is independent of primitive
cell convention, based on the bispectrum–a descriptor built from spherical harmonic projections of
lattice points. The calculation of the
lattice bispectrum is differentiable, and we demonstrate how to invert it using gradient-based optimization initialized from a nearest-neighbor lookup. We show that with a fixed ML model architecture, using the
lattice bispectrum as the ML target rather than the unit
cell parameters leads to more accurate
lattice parameter predictions. For example, using the MP-20
dataset, the bispectrum reduces length mean absolute percentage error (MAPE) from 11.08% to 2.43% and angle MAPE from 12.15% to 2.45% compared to direct prediction with the same model architecture. We additionally
benchmark our approach against pre-existing XRD to
crystal structure models such as Crystalyze and assess its performance on experimental data. Beyond unit
cell representation, we anticipate this invariant
lattice representation could serve more broadly as a geometry-aware target for other crystallographic machine learning tasks such as structure generation.
Read the full abstract ▾
All authors Elyssa Hofgard, Kyucheol Min, Nofit Segal, David W. Mittan-Moreau, Aria Mansouri Tehrani, Vanessa Oklejas, Rafael Gómez-Bombarelli, Jigyasa Nigam, Daniel W. Paley, Aaron S. Brewster, Tess Smidt
Strongly Correlated Electrons
Hydrodynamic Memory and Long-Time Tails in Clean Frustrated Magnets
Yufei Pei, Claudio Castelnovo and Roderich Moessner
In a simple, clean but constrained magnet, we identify a self-interacting random walk with
memory. For the motion of a single monopole – a fractionalized quasiparticle in
spin ice – this produces a subtle and unusually slow relaxation toward diffusive motion. This is manifested as an algebraic long-time tail in the velocity autocorrelation function, decaying as $t^{-3/2}$. At finite monopole density, the interactions between the trails of different monopoles introduce an additional timescale, corresponding to the disruption of a monopole's
memory by other monopoles, and leading to an exponential cutoff of the long-time tail. Our results identify clean frustrated magnets as microscopic platforms for studying self-interacting
stochastic processes, hydrodynamic
memory, and the emergence of non-Markovian quasiparticle transport from local Markovian dynamics.
Read the full abstract ▾
Soft Condensed Matter · Cross-listed from math.DS
The two momenta of an elastic rod: a Hamiltonian picture on framed Lie groups
Thomas Lessinnes
The
equilibrium equations of elastic rods can be obtained by balancing forces and moments, or by rendering a potential energy stationary. For complex filaments the energy route asks less of one's mechanical intuition. However, in the classical
Hamiltonian picture, the components of the generalized momenta are postulated a priori and their physical meaning changes at the whim of the coordinate chart. Here, we draw on two ideas from mathematical physics. First, the extended tangent bundle of the configuration Lie group is framed by left-invariant vector fields. Second, we follow a one-dimensional reading of the Cartan–Lepage–Krupka theory of variational forms: in this setting the momenta are not postulated but forced. The Legendre transform becomes a linear change of frame, and a Poisson structure on the extended tangent bundle follows. For an isolated Cosserat rod, the momenta coincide, in every encoding of the rotation group, with the material force and moment familiar from rod theories. In the presence of interactions, two cases arise: interactions that depend only on the configuration, such as
gravity, leave this identification intact; interactions that depend on the strains destroy it — the conjugate momenta and the internal stresses part company. Because energies add, the momenta decompose into the internal stresses and an interaction contribution. Expressing the two factors of the Poisson bivector in different frames — one adapted to the internal stresses, the other to the conjugate momenta — then exposes the
Hamiltonian flow directly in the internal variables. Applied to a tendon-actuated rod, where the standard passage to the
Hamiltonian picture demands a nonlinear inversion, the construction delivers explicit
equilibrium equations, the required inversion collapsing to a rank-one correction.
Read the full abstract ▾
Soft Condensed Matter
Quantifying reticulocyte biomechanics in health and disease
Zhaojie Chai, Jianlu Zheng, He Li et al. (+2 more)
Red blood
cell (RBC) populations are mechanically and morphologically heterogeneous, yet how this heterogeneity governs transport, splenic retention and blood rheology in confinement remains unclear. We combine microchannel experiments with dissipative particle dynamics (DPD) simulations to determine how the morphology, deformability and hydrodynamic interaction of immature RBCs (reticulocytes) shape microconfined flow in acute and chronic mountain sickness. Reticulocyte-rich samples present the three shapes that the maturation literature assigns to successive reticulocyte stages – multilobular, cup-shaped and near-discocytic – which we model as R1-R3, each with a membrane shear modulus within the range reported for reticulocytes. A 5-um microchannel resolves these models only weakly, R1 taking at most ~18% longer than control discocytes to cross it, whereas a 1.5-um splenic slit, driven at its own loading, delays R1 by ~30%; both geometries order the models by shear modulus. In
cell pairs, a leading
cell never lets a follower pass below its own single-
cell threshold, ruling out the order-of-magnitude reduction that a wake-"unjamming" picture would suggest; instead the follower queues behind the leader, and a stiffer leader, which clears the slit more slowly, delays it more. The controlling variable is the single-
cell critical pressure gradient Delta P_c, which rises monotonically from control discocytes through the reticulocyte subtypes to sickled
cells. Set against published rheograms, an analytical estimate attributes chronic-mountain-sickness hyperviscosity mainly to hematocrit-driven crowding rather than single-
cell rheology. These results place benign acclimatization, chronic-mountain-sickness hyperviscosity and sickle-
cell-trait splenic syndrome on a single mechanical axis defined by Delta P_c.
Read the full abstract ▾
All authors Zhaojie Chai, Jianlu Zheng, He Li, Ming Dao, George Em Karniadakis
Mesoscale and Nanoscale Physics
Observation of room temperature intrinsic nonlinear thermoelectric effects in low-dimensional semimetals
Kurea Nakagawa, Krishnaraajan Sundararajan, Cédric A. Cordero-Silis et al. (+2 more)
Nonreciprocal control of thermoelectric responses offers a promising strategy for next-generation thermal-management and energy-conversion. While nonlinear electrical transport has recently emerged as an intrinsic property of low-
symmetry quantum materials, their thermoelectric counterparts have not been demonstrated. Here, exploiting harmonic detection with gradient-reversal techniques, we report intrinsic nonlinear thermoelectric responses up to room temperature in the low-
symmetry type-II Weyl semimetals $T_\mathrm{d}$-WTe$_2$ and TaIrTe$_4$ in the absence of
magnetic fields or
magnetic materials. We resolve all
symmetry-allowed components of the second-order thermoelectric tensor, including the nonlinear Seebeck, nonlinear Nernst, and nonlinear mixed-directional thermoelectric effects and demonstrate that both Berry-
curvature-related and scattering-induced contributions govern the different nonlinear thermoelectric responses. Our results show that nonlinear thermoelectricity arises intrinsically from reduced
crystal symmetry and that engineering effects related to scattering in these materials provides a versatile platform for exploring higher-order heat-to-charge current conversion beyond the linear response.
Read the full abstract ▾
All authors Kurea Nakagawa, Krishnaraajan Sundararajan, Cédric A. Cordero-Silis, Bart J. van Wees, Marcos H.D. Guimarães
Strongly Correlated Electrons
Intrinsic single crystals of MnTe altermagnet
Kim-Khuong Huynh, Michael Anthony Quintero, Martin Klanjšek et al. (+8 more)
We report the synthesis methodology, structure, and intrinsic properties of ultra-high quality single
crystals of MnTe, an archetypal altermagnet. The
crystals, obtained from self-flux method, are nearly free from
crystal imperfections and disproportionate chemical compositions as seen by various investigation methods. In measurements under quasi free-standing configuration minimizing stress induced effects, the
crystals exhibit complex and anisotropic domain kinetics in both superheating and supercooling regimes around the altermagnetic transition at $T_{\mathrm{N}} = 310\,\mathrm{K}$. An Anderson insulating state is observed below $T_{\mathrm{MI}}\approx 150\,\mathrm{K}$ with a carrier density of about $1.6\times 10^{17}\,\mathrm{cm}^{-3}$, being sharply contrast to metallic states usually seen in Te-deficit samples. Nevertheless, hallmarks of altermagnetism, anomalous
Hall effect and X-ray
magnetic circular dichroism signal, are robust in this intrinsic limit, however with significantly reduced magnitudes.
Read the full abstract ▾
All authors Kim-Khuong Huynh, Michael Anthony Quintero, Martin Klanjšek, Tilen Knaflič, Yuta Ishii, Norimasa Sasabe, Nhu-Quynh T. Phan, Frej Søren Rattenborg, Yuichi Yamasaki, Denis Arčon, Bo Brummerstedt Iversen
Superconductivity
Thermal phase slips in superconducting films near the critical current at arbitrary temperatures
Ivan M. Artemov and Mikhail A. Skvortsov
We develop a theory of thermal phase slips in disordered superconducting films biased near the critical current $I_c(T)$. Generalizing recent results obtained close to $T_c$, we show that the optimal fluctuation governing the phase-slip barrier in two dimensions satisfies the exactly integrable Boussinesq equation for arbitrary temperatures $T<T_c$. Since both the transverse and longitudinal sizes of the optimal
nucleus diverge as $I\to I_c(T)$, the Usadel equation for quasiparticles in the presence of a slowly varying order parameter can be solved perturbatively using a gradient expansion. The resulting field theory for a complex order parameter is further reduced to the Boussinesq free energy for a single real field, with the coefficients expressed as Matsubara sums over the solutions of the uniform Usadel equation at $I_c(T)$. The activation barrier near $I_c$ has the asymptotic form $\Delta F(T,I\to I_c) = E(T) (1-I/I_c)^\alpha$. We calculate $E(T)$ over the full temperature range for both two-dimensional films ($\alpha=3/4$) and one-dimensional wires ($\alpha=5/4$). For films, the theory is valid within a narrow $10\%$ window below $I_c(T)$, where the saddle-point configuration remains
vortex-free. For wires, $\Delta F(T,I\to I_c)$ provides a good approximation to the activation barrier for all temperatures and currents.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Tunable nonlinear electromechanics at the zero-point motion scale
Christoffer B. Møller, Roger Tormo-Queralt, Elsa Vázquez-Rodríguez et al. (+13 more)
Nonlinearity at the scale of zero-point motion opens new possibilities for the control and readout of nanomechanical systems, but achieving this remains a formidable challenge. Here we demonstrate that ultrastrong coupling (USC) between a nanotube mechanical oscillator and a double-
quantum-dot electronic two-level system enables a mechanical Kerr (Duffing) nonlinearity at the zero-point motion scale. In the dispersive regime, this large coupling yields a mechanical anharmonicity of $\alpha = 1.4\%$ - three orders of magnitude larger than in previous work - while preserving the predominantly mechanical nature of the lowest energy states. We further demonstrate a purely quadratic cavity-based continuous readout of the mechanical motion. This continuous nonlinear optomechanical readout is enforced by a double-
quantum dot
symmetry, which can be broken by gate tuning to introduce a large linear transduction. These results establish a tunable USC platform that enables strong mechanical anharmonicity and nonlinear continuous readout at the zero-point motion scale.
Read the full abstract ▾
All authors Christoffer B. Møller, Roger Tormo-Queralt, Elsa Vázquez-Rodríguez, Victor Román-Rodríguez, Marta Cagetti, Eneko Mateos-Madinabeitia, Janine C. Franz, Stefan Forstner, Sergio L. De Bonis, Luca Ornago, Maria El Abbassi, Seoho Jung, Andrew N. Cleland, David A. Czaplewski, Fabio Pistolesi, Adrian Bachtold
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Towards on-chip nascent all-van-der-Waals polarization optical components for nanoscale photonic applications
Dmitrii Litvinov, Ilia Begichev, Iakov Reznikov et al. (+8 more)
The integration of polarization-control elements into nanoscale photonic
circuits remains a central challenge for modern on-chip optical technologies, which call for continuous miniaturization. Van der Waals (vdW)
crystals provide a versatile platform for the creation of such components owing to their strong optical anisotropy, high-refractive indices and atomically precise
heterostructure assembly capabilities. In this work, we demonstrate an approach towards the creation of all-vdW on-chip polarization optical components, exemplified with quarter-wave plates operating in the near-infrared (NIR) spectral region, realized in specifically twisted ReSe2/alpha-MoO3 vdW
heterostructures on a Si/SiO2 platform. Here, low-
symmetry ReSe2 layer serves as a source of exceptionally high linearly polarized excitonic emission, whereas in-plane birefringent alpha-MoO_3 provides polarization-state conversion. Furthermore, our finite-difference time-domain (FDTD) simulations quantitatively reproduce the experimental observations with high accuracy revealing the critical roles of layer thicknesses, twist-angle, Fabry-Perot interference and emitter distribution effects in the determination of polarization conversion efficiency, which yields up to 95 % degrees of circular polarization (DoCP) for the optimized parametrization. Our findings establish a practical route towards fully integrated all-vdW polarization optical components, providing a foundation for nanoscale photonic architectures based entirely on layered materials.
Read the full abstract ▾
All authors Dmitrii Litvinov, Ilia Begichev, Iakov Reznikov, Changyi Chen, Maksim Sargsyan, Sergey Y. Grebenchuk, Makars Siskins, Kostya S. Novoselov, Alexey I. Berdyugin, Maciej Koperski, Davit A. Ghazaryan
Strongly Correlated Electrons · Cross-listed from quant-ph
Quantum Cellular Automata from Kramers-Wannier Dualities and Modular Relations
Carolyn Zhang and Po-Shen Hsin
Recent work has constructed higher-dimensional analogs of non-invertible
symmetries similar to 1+1d Kramers-Wannier duality. Although their continuum descriptions often treat purely gravitational topological terms as inessential counterterms, these terms can have an essential
lattice manifestation: they distinguish states prepared by finite-depth
quantum circuits (FDQCs) from those entangled by nontrivial
quantum cellular automata (QCAs). Motivated by this mismatch, we show that QCAs associated with gravitational topological responses arise in several related settings: (1)
lattice realizations of projective $\mathrm{SL}(2,\mathbb{Z}_N)$ relations generated by topological operations on
symmetries; (2) squares of dualities that generalize the relation between fermionization and Kramers-Wannier duality; (3)
lattice implementations of QCAs through higher-form gauging; and (4) invertible phases protected by generalized time-reversal
symmetries. We derive new projective $\mathrm{SL}(2,\mathbb{Z}_N)$ relations whose projective phases are gravitational topological responses constructed from Stiefel-Whitney classes. We furthermore give a general protocol for preparing the associated QCA-entangled states using finite-depth
unitary circuits, measurements, and error correction. These results unify the study of gravitational topological responses in field theories, higher dimensional dualities, and
quantum cellular automata.
Read the full abstract ▾
Materials Science
Ionic Diffusion Properties of Rare-Earth High-Entropy Oxides from a Machine-Learned Interatomic Potential
Mary Kathleen Caucci, Billy E. Yang, Saeed S.I. Almishal et al. (+2 more)
Rare-earth high-
entropy oxides (RE-HEOs) have emerged as a promising class of functional ceramics for solid-state electrochemical applications due to their chemical complexity, structural tunability, and potential for fast oxygen-ion transport. In this work, we investigate oxygen
diffusion in ceria-based RE-HEOs of the form Ce$_x$(YLaPrSm)$_{1-x}$O$_{2-\delta}$ using classical molecular dynamics simulations driven by the
Crystal Hamiltonian Graph Neural Network (CHGNet) machine-learned interatomic potential. To improve predictive accuracy for lanthanide-containing systems, we
benchmark three CHGNet variants, including a fine-tuned r$^2$SCAN-trained model, against targeted density functional theory (DFT) data that explicitly include f-valence electrons. Simulations across temperature, Ce content, oxygen vacancy concentration, and both fluorite and bixbyite structures reveal that oxygen transport in RE-HEOs is governed by the interplay of two factors: the concentration of mobile vacancies and the local cation environment through which they hop. At fixed composition, ionic conductivity exhibits a non-monotonic dependence on vacancy concentration, with optimal
diffusion occurring at moderate vacancy levels and reduced mobility at higher concentrations. Increasing Ce content lowers migration activation energies and enhances diffusivity through low-barrier
diffusion networks built from Ce-Ce and Ce-Y edges. Analysis of individual oxygen hopping events provides atomistic insight into how local chemical environments and short-range cation ordering govern transport in high-
entropy oxides. Overall, this work demonstrates that machine-learned interatomic potentials can resolve composition-structure-transport relationships in chemically complex
oxides, and identifies active pathways through which compositional tuning can enhance oxygen-ion conductivity in RE-HEO materials.
Read the full abstract ▾
All authors Mary Kathleen Caucci, Billy E. Yang, Saeed S.I. Almishal, Jon-Paul Maria, Susan B. Sinnott
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Electron shuttling as a probe for charge defects
Hamza Jnane, Tamas Daniel Lipovics and Guido Burkard
Silicon
spin qubits are a leading platform for scalable
quantum computing, but their performance is limited by charge noise, widely attributed to two-level fluctuators (TLFs). The location of individual TLFs is generally unknown, and existing methods to localise them does not scale favourably with device size. Here, we show that electron shuttling turns a single mobile
spin into a scanning probe of individual defects. We show that by shuttling a
spin over a range of distances and tracking its coherence loss, one can localise defects along the channel and constrain their switching rate and fluctuation amplitude. Because one shuttled electron sweeps an extended region, the approach scales more favourably than previous methods. Our protocol requires no additional hardware and provides a practical route to mapping the charge-defect landscape of large silicon devices, enabling defect-aware calibration and avoidance in shuttling-based architectures.
Read the full abstract ▾
Disordered Systems and Neural Networks
Thermal avalanches in a quasiperiodic XXZ model
Paolo Molignini and Antonio Štrkalj
We study bath-induced thermalization in the many-body localized XXZ
spin chain subjected to a quasiperiodic
magnetic field. We engineer a thermal inclusion by setting the field strength in one part of the chain below the localization threshold and analyze thermalization via the avalanche mechanism. To study the nature of such avalanches, we use two complementary observables, namely the two-point connected correlation function and the particle-number
entropy. Surprisingly, the correlations alone show no signatures of avalanches. Instead, they display a logarithmic growth of the correlation length throughout the dynamics and predict localization lengths of the local integrals of motion that remain well below the avalanche threshold. In contrast, the particle number
entropy shows clear signatures of the thermal avalanche, with the avalanche front progressively propagating deeper into the localized subsystem for sufficiently large baths. The discrepancy between the two observables shows that two-point correlations are unreliable in identifying thermal avalanches in quasiperiodic systems, as opposed to the random case. On one hand, qualitative results are consistent with the analytical predictions of the standard avalanche theory. On the other hand, significant quantitative deviations persist, which could be due to short-range resonances generated by the quasiperiodic potential. Our results suggest that the standard avalanche framework requires revision to account for the short-range correlations of quasiperiodic potentials.
Read the full abstract ▾
Strongly Correlated Electrons · Cross-listed from quant-ph
Resolving topological order crossovers on NISQ hardware
Ruizhe Shen, Yin Zhong and Ching Hua Lee
Topological phases of matter provide a promising route toward robust
quantum information processing, but on present-day noisy intermediate-scale
quantum devices the experimentally relevant question is whether signatures of topological crossovers remain resolvable under realistic imperfections. Here, we address this question in the Wen–plaquette model through a two-stage strategy on the IBM
Quantum hardware. We first use a tractable system to systematically characterize crossover signatures. Using variationally compiled
equilibrium and quench-generated states, we resolve crossovers between stabilizer-dominated and trivial or disorder-dominated regimes through local plaquette stabilizers and a Wilson loop, and quantify their robustness against static disorder, deliberately amplified
circuit noise, and effective non-Hermitian fields. The quench dynamics further reveal that plaquette-sector signatures remain substantially more stable deep in the strong-stabilizer regime than near the finite-size crossover. Building on the properties established in the small system, we extend the implementation to a physical two-dimensional IBM processor using a layered representative-
qubit construction. The resulting
lattice-averaged plaquette response exhibits only weak degradation under intentionally amplified local coherent perturbations. Together, these results connect controlled finite-size characterization with a scalable hardware implementation, providing a practical route for preparing and probing topological signatures on near-term
quantum processors.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Mixed-state topological order and error-correction thresholds in non-Abelian codes: rigorous results
Sun Woo P. Kim and Max McGinley
We present a versatile and mathematically rigorous technique for bounding recovery thresholds in topological codes subject to noise. Our method captures the effect of applying an arbitrary (possibly non-Pauli) local noise channel to the code state of a broad class of two-dimensional codes, including surface codes, non-Abelian
quantum doubles, and string-net codes. In each case, we prove that for noise strengths up to some explicit constant value, any initially encoded logical information can be recovered to high precision, and that the noise-corrupted state exhibits key hallmarks of mixed-state topological order: long-range
entanglement and emergent higher-form
symmetries. We also describe how these methods can be adapted to higher dimensions and correlated noise models.
Read the full abstract ▾
Strongly Correlated Electrons
Counting Edge Modes with the Higher Berry Curvature: A Bulk Topological Order Parameter for Quantum Spin Chains
Adam J. McRoberts, Joe Crossley, Chris Hooley et al. (+1 more)
We show that the higher Berry
curvature (HBC) can be used to count the gapless edge modes created by an
entanglement cut, and thus defines an integer-valued topological order parameter for
quantum spin chains. Given an individual
spin-chain
Hamiltonian, we construct an extending family by interpolating to a reference product Néel state, and show that the integral of the HBC over this extension is equal to the ordinary Berry phase of half of the chain swept out in response to an infinitesimal field. It thus counts the
spin of the gapless edge modes exposed by the cut, and a change in its integer value signals a phase transition. We illustrate this with several examples: $S=1/2$, $S=1$, and $S=3/2$
spin-Peierls chains, which undergo `singlet flop' transitions between different patterns of dimerisation; the bilinear-biquadratic chain, which clarifies the connection to the strict
symmetry-protected topological phases classification; and the staggered $J_1$–$J_2$ chain, which has both nearest-neighbour and third-neighbour patterns of singlets depending on the signs of the interactions.
Read the full abstract ▾
All authors Adam J. McRoberts, Joe Crossley, Chris Hooley, Joe H. Winter
Mesoscale and Nanoscale Physics
Real-Space Imaging of Band Topology via Wavefunction Zeros
Julian Ingham and Raquel Queiroz
We prove that the wavefunction of a
crystal at a high-
symmetry momentum, $\Psi_{\boldsymbol{k}_*}(\boldsymbol{r})$, has
symmetry-enforced zeros at certain positions in the unit
cell, using a new invariant fixed uniquely by the symmorphic
symmetry representation of the wavefunction. This allows one to infer the
topology of an electronic band by probing zeros of the charge density, and in turn to connect scanning tunnelling microscopy to the group representation theory of bandstructure. We apply the
theorem to 1H transition metal dichalcogenides, where it detects the obstructed atomic limit of WSe$_2$, the Haldane model, where it detects the Chern number modulo three, and the Bernevig-Hughes-Zhang model, where it detects the $\mathbb{Z}_2$ index. In addition, the zeros have important consequences for interaction effects: in kagome metals, they fix the sublattice structure of Van Hove wavefunctions, and in twisted
bilayer graphene, they explain the qualitative interaction-induced reshaping of the flat bands.
Read the full abstract ▾
Strongly Correlated Electrons · Cross-listed from quant-ph
Non-Invertible Symmetries Mixing with Witt Non-Trivial Quantum Cellular Automata
Kansei Inamura, Oskar Wojdel, Lukasz Fidkowski et al. (+1 more)
Self-dualities and the stacking of
symmetry-protected topological (SPT) phases are basic operations on
quantum many-body systems. For a $\mathbb{Z}_p$ one-form
symmetry in 3+1d these correspond to the Kramers-Wannier-Wegner duality $S$, which is the gauging operation underlying non-invertible duality
symmetries, and the stacking of a 1-form
symmetry SPT $T$. In the continuum, they form a central extension of $PSL(2,\mathbb{Z}_4)$ for $p=2$, and of $SL(2,\mathbb{Z}_p)$ for odd
primes $p$, whose central elements are invertible theories with purely gravitational response. These central extensions are governed by a twisted, graded generalization of the Witt group of abelian anyon theories, which we determine. For $p=2$ the resulting group is the single-
qubit Clifford group, with duality and entangler acting as the Hadamard and phase gates. We realize this entire structure microscopically as
quantum cellular automata (QCA) acting on a certain local operator
algebra associated with a
spin lattice Hilbert space on a cubic
lattice. Specifically, our local operator
algebra is built by starting with all local operators commuting with a $\mathbb{Z}_p$ 1-form
symmetry, and taking the quotient by all the (local) 1-form
symmetry generators. The central elements can always be extended to the full tensor product
algebra with a uniquely defined QCA class. For $p=2$ they are generated by the non-trivial semion QCA, and for odd
prime $p$ they are generated by the non-trivial $\mathbb{Z}_p$ Clifford QCA. Consequently the
lattice fusion rules reproduce the continuum ones only up to these QCAs and
lattice translations, giving rise to fusion rules refined by QCAs.
Read the full abstract ▾
All authors Kansei Inamura, Oskar Wojdel, Lukasz Fidkowski, Sakura Schafer-Nameki
Strongly Correlated Electrons · Cross-listed from quant-ph
Non-Clifford quantum cellular automata from invertible topological quantum field theories
Meng Sun, Zongyuan Wang, Bowen Yang et al. (+2 more)
Quantum cellular automata (QCAs) describe locality-preserving
quantum dynamics and connect
quantum information, many-body physics, and topological
quantum field theory (TQFT). Constructing a QCA from a TQFT, however, is challenging. Although a topological action can produce a commuting
Hamiltonian realizing the desired ground state, it does not by itself specify an
automorphism of the full local operator
algebra. In this work, we develop a unified algebraic construction that extends the commuting generators of the
Hamiltonian to a complete separator-flipper
algebra on the full tensor-product
Hilbert space, providing a microscopic definition of the corresponding QCA. In three spatial dimensions, our formalism unifies all previously known QCA constructions associated with the $\mathbb Z_8\times\mathbb Z_2$ subgroup of the Witt group, including the $U(1)_2$ and $U(1)_4$ QCAs. The same algebraic structure directly yields new infinite families of generalized $U(1)_2$ and $U(1)_4$ non-Clifford QCAs in dimensions $d=4k-1$. We also reformulate the 4-dimensional $w_2w_3$ QCA and use it to develop a general construction of QCAs from TQFTs associated with arbitrary products of Wu classes. This construction includes two infinite families. The first consists of $w_2^nw_3^m$ QCAs in dimension $d=2n+3m-1$, while the second consists of $w_2w_{4k-1}$ QCAs in dimension $d=4k$. As a contrasting result, we explicitly construct finite-depth
quantum circuits for the 5-dimensional $w_3^2$ and $w_2^3$ QCAs, thereby proving that they are trivial, in agreement with the cobordism classification. Overall, these results convert invertible TQFTs into microscopic QCAs, provide a scalable route to higher-dimensional constructions beyond the Clifford setting, and open a systematic approach to classifying their stable structures and boundary anomalies.
Read the full abstract ▾
All authors Meng Sun, Zongyuan Wang, Bowen Yang, Nathanan Tantivasadakarn, Yu-An Chen
Materials Science
Symmetry-Adapted Physical and Vibrational Properties of Ferroelectric Perovskite Oxides: Application to PbZrxTi1-xO3
Sumit Ranjan Maity and Brajesh Tiwari
Crystal symmetry governs macroscopic physical properties and
lattice dynamics in functional materials. We present a systematic application of tensor analysis and group theory to determine allowed physical-property tensors, vibrational-mode
symmetries, and Raman selection rules directly from crystallographic point-group
symmetry. The approach is applied to the prototypical ferroelectric PbZrxTi1-xO3 (PZT).
Symmetry lowering across the PZT phase diagram increases the number of independent pyroelectric, dielectric, and piezoelectric tensor components and modifies the
symmetry classification of Raman-active vibrations. These mode classifications enable
symmetry-based decomposition of reported room-temperature powder Raman spectra as a function of composition (x) across the morphotropic phase boundary, revealing the tetragonal-to-rhombohedral transition as a continuous redistribution of spectral intensity rather than emergence of new Raman modes. Persistent subpeak structure in selected modes indicates local
symmetry breaking due to cation disorder and
lattice anharmonicity, underscoring the importance of crystallographic
symmetry analysis for interpreting functional and vibrational properties of ferroelectric perovskite
oxides.
Read the full abstract ▾
Statistical Mechanics · Cross-listed from quant-ph
Tunable Mpemba Effect in a Prethermal Many-Body Spin Network
Chaitali Shah, Cooper M. Selco, Leo Joon Il Moon et al. (+1 more)
Relaxation in an interacting system is determined not only by its initial distance from
equilibrium, but also by the relaxation modes populated by the initial state. Here we experimentally observe and control the Mpemba effect, in which a state farther from
equilibrium overtakes one initially closer, in an extended, disordered $^{13}$C
nuclear-
spin network in diamond. Field cycling allows us to prepare distinct spatial polarization profiles by independently controlling hyperpolarization and defect-mediated relaxation. We then track their
evolution under Floquet driving, which stabilizes a long-lived prethermal regime. We observe reproducible Mpemba crossings and tune the crossing time over several orders of magnitude, from late-time thermalization into the prethermal plateau. Semiclassical simulations show that randomly positioned paramagnetic defects create fast-relaxing regions and defect-poor regions that support the slowest collective relaxation mode. The Mpemba crossings are set by the initial state overlap with this mode. Our results demonstrate anomalous relaxation within a prethermal many-body regime and identify disorder, transport, and mode-selective state preparation as resources for controlling relaxation in extended
spin networks.
Read the full abstract ▾
All authors Chaitali Shah, Cooper M. Selco, Leo Joon Il Moon, Ashok Ajoy
Quantum Gases
Complexity transition in the Dicke model of light-matter interaction
Yicheng Zhang and Erhai Zhao
Tuning the coupling strength $g$ of an interacting
quantum system may drive a sudden change in its ground-state or thermal properties. To identify and grasp non-analytical, or even discontinuous, transitions in far-from-
equilibrium dynamics proves more challenging. Recently Krylov complexity $C_K$ has offered fresh insights about operator growth, thermalization, and chaos in
quantum dynamics. Yet it remains unclear if, and how, changing $g$ can trigger a sharp transition in the complexity measures. Here we present evidence for such a transition by mapping out the complexity phase diagram of the paradigmatic Dicke model describing two-level atoms coupled to a cavity
photon mode. Two qualitatively different regimes of dynamics are identified and characterized. At the transition, the slope of $C_K$ changes suddenly to coincide with a jump in the Krylov
entropy. We elucidate the nature of the regime change from the wave packet dynamics in Krylov space, where a particle is confined by a roughly linear potential but hops as if it lives in a Rindler reference frame. The competition between confinement, which leads to bouncing, and deconfinement by Rindler hopping, which leads to the destruction of wave packet analogous to gravitational spaghettification, is sensitive to the disorder in Lanczos coefficients. The framework outlined here can be applied to other
quantum many-body systems.
Read the full abstract ▾
Strongly Correlated Electrons
Ziwei Wang, Charlie Raca and Steven H. Simon
Quantum geometric quantities have featured heavily in the discussion of the properties of
quantum systems in recent years. Among quantities most commonly discussed is the variance of Berry
curvature and the integral of the trace of the
quantum metric tensor. Despite their usefulness, it is known that they suffer from one significant complication: for a tight-binding model, the
quantum geometric quantities depend not only on the parameters of the tight-binding model itself, but also the real space geometry of the tight-binding model, the so-called "orbital
embedding". One explicitly geometry-independent quantity is therefore the minimal value of the
quantum geometric quantity out of all possible real space geometries. In this work, we demonstrate that, if the tight-binding model is compatible with certain spatial
symmetries, then the real space geometry that minimizes the variance of the Berry
curvature or the integral of the trace of the
quantum metric tensor must obey all those spatial
symmetries. We further show that the statement is applicable to systems with
magnetic translation
symmetries and other composite
symmetries, with implications for the
quantum geometry of the Hofstadter model.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
An integrated all-van der Waals nanobeam laser
Aris Koulas-Simos, Pietro Metuh, Athanasios Paralikis et al. (+7 more)
Transition-metal dichalcogenides offer a promising platform for integrated coherent light sources, yet lasing has largely relied on hybrid photonic architectures without direct
quantum-optical verification. Here, we demonstrate an all-van der Waals (all-vdW) high-$\beta$ nanobeam
laser based on a WS$_2$/MoSe$_2$/WS$_{2}$
heterostructure, with the MoSe$_2$ monolayer directly integrated in the WS$_{2}$-based optical resonator for optimal gain-mode overlap. The devices exhibit efficient
exciton-cavity coupling at cryogenic temperatures, strongly directional and linearly polarized emission, soft nonlinear input-output characteristics and linewidth narrowing, enabling lasing operation with $\beta$ near unity. Excitation-power-dependent
photon-autocorrelation measurements reveal a transition from thermal to Poissonian
photon statistics, with $g_{\mathrm{peak}}^{(2)}(0)$ decreasing from $(1.28\,\pm\,0.09)$ near threshold to $(1.07\,\pm\,0.07)$ above threshold, directly verifying lasing operation. Furthermore, temporal broadening of the autocorrelation uncovers fluctuation-dominated lasing dynamics. These results establish all-vdW
heterostructures as a highly attractive platform for integrated coherent light sources in layered-material photonic architectures and scalable
quantum-photonic
circuits.
Read the full abstract ▾
All authors Aris Koulas-Simos, Pietro Metuh, Athanasios Paralikis, Kartik Gaur, Maximilian Klonz, Imad Limame, Bárbara L. T. Rosa, Chirag C. Palekar, Battulga Munkhbat, Stephan Reitzenstein
Statistical Mechanics · Cross-listed from quant-ph
Beyond Calabrese-Cardy Scaling: Exceptional-Point Sensitivity and the de Sitter RT Surface
Kuang-Hung Chou
Entanglement entropy at one-dimensional criticality typically follows the Calabrese–Cardy scaling. In the non-Hermitian critical free-
fermion systems studied here, however, we find an additional interval-independent contribution $S_{\rm res}=\log(\Delta L)$, which allows the
entropy to remain sensitive to energy gaps below the finite-size scale, $\Delta<1/L$. We refer to this term as the residual
entropy. To understand its infrared origin, we examine finite-depth non-
unitary continuous multiscale
entanglement renormalization on a ring. Terminating the critical RG
circuit before its singular final layer leaves a two-site infrared state. We calculate the
entropy of this state directly from its correlation
matrix and recover the same \(\log(\Delta L)\) dependence. The emergent de Sitter geometry provides a complementary
geometric interpretation: extremal curves associated with different boundary intervals extend to a common infrared endpoint, suggesting how the
entanglement retained there can contribute equally to their
entropies.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Probing the nonlocality of Landau levels in GaAs quantum wells through modified Purcell factors, Lamb shifts and dipole emitted spectra
Lara Greten, Sabrina Meyer, Christina Schröder et al. (+2 more)
In a two-dimensional electron gas, a strong perpendicular
magnetic field confines electrons to quantized cyclotron orbits, giving rise to Landau levels with discrete orbit radii. Even the smallest Landau orbit, set by the
magnetic length, spans tens of nanometers for fields of a few Tesla, imposing an intrinsic nonlocal response to electromagnetic excitations. From a microscopic theory of the nonlocal susceptibility, we derive the Green's function, the central quantity governing all electromagnetic interactions, and evaluate Purcell factors, Lamb shifts, and emission spectra from a proximal dipole emitter beyond the Markov and rotating-wave approximations. Significant nonlocal effects resulting from spatial dispersion of the Landau level response modify the response for experimentally relevant situations up to distances of hundreds of nanometers and, in particular, brighten locally dipole-forbidden transitions due to near-field gradients at multiples of the cyclotron frequency. The relevant length scales are typical of state-of-the-art nanostructured terahertz architectures, and some of our nonlocal features are consistent with recent experiments using Landau level polaritons.
Read the full abstract ▾
All authors Lara Greten, Sabrina Meyer, Christina Schröder, Andreas Knorr, Stephen Hughes
Superconductivity
Sequential Topological Superconductivity in a Square Lattice with Chiral Charge Density Waves
Zhong-Xian Jin, Junkang Huang, Yu-Xuan Li et al. (+1 more)
The interplay between charge order and superconductivity offers a fertile ground for emergent
quantum phases. Here we theoretically investigate a square-
lattice superconductor coexisting with a composite charge density wave (CDW) consisting of a real bond modulation (charge bond order, CBO) and an imaginary hopping modulation (
chiral flux phase, CFP) that breaks time-reversal
symmetry. We uncover that, while CFP alone does not induce
topology in square
lattices, its coexistence with CBO drives the system into two topologically nontrivial superconducting phases with Chern numbers $C=+2$ and $C=-2$. The low-temperature thermal
Hall conductivity $\kappa_{xy}$ exhibits quantized plateaus proportional to the Chern number, providing a clear experimental fingerprint. Our results establish the square
lattice as a pristine platform for engineering topological superconductivity through the synergy of real and imaginary bond modulations.
Read the full abstract ▾
All authors Zhong-Xian Jin, Junkang Huang, Yu-Xuan Li, Tao Zhou