Statistical Mechanics · Cross-listed from quant-ph
Statistical Mechanics of Non-Abelian Learnability Transitions
Ruochen Ma and Romain Vasseur
Monitored many-body
quantum systems can undergo sharp learnability transitions characterized by how much information can be learned by the observer. When the dynamics conserves a non-Abelian charge, such as an $SU(2)$
spin, understanding how the observer learns the total charge remains an outstanding problem. Unlike the Abelian case, where charge measurements on distinct sites commute, the $SU(2)$-symmetric readouts are noncommuting fusion measurements, making learning a genuinely
quantum inference problem. In this work, we propose a theory of $1+1d$ monitored
quantum dynamics with $SU(2)$
symmetry, and show that it can be described by an effective replicated loop model comprised of a replica-pairing field and a diffusive ($z=2$) background sector that carries the $SU(2)$ charge and remains gapless throughout the phase diagram. Our theory predicts that the "
spin-sharpening” and
entanglement transitions coincide as a single transition. Ordering of the pairing field produces volume-law
entanglement and hides the background sector from measurements, leading to a learning time of $t\sim L^{3}$ for the total
spin. When the pairing field disorders, the background sector alone gives logarithmic
entanglement and a diffusive learning time $t\sim L^{2}$. Our analysis is controlled by a large-loop-fugacity expansion.
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Statistical Mechanics
Quantum Rényi-Jarzynski Equality
Benjamin Bobell, Mert Okyay and Rahul Nandkishore
The Jarzynski equality provides a strict link between nonequilibrium work and
equilibrium free energy changes. Its typical
quantum formulations, however, rely on measurement protocols that destroy coherence. In this Letter, we use the resource-theoretic approach to derive a non-destructive
quantum Jarzynski equality conditioned on the outcomes of an arbitrary bath observable. This yields the Rényi-Jarzynski equality, which quantifies a finite bath's drift from
equilibrium under a non-adiabatic drive via the Rényi $k$-divergence. We further demonstrate that the Rényi-Jarzynski equality provides a tunable cost function for
quantum optimal control problems where minimizing bath drift is desired, such as state preparation and gate design, enabling the minimization of cross-talk in finite
quantum systems. Our toy model exhibits a transition between competing minima for some critical value of $k$, illustrating how the Rényi order tunes sensitivity to different regions of a bath distribution. Strikingly, when drive parameters vary across bath energy levels, minimizing bath drift requires generating system-bath
entanglement.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Simulating Black Hole Thermality and Interior Scrambling on a Superconducting Quantum Processor
Ryan Smith, Ewan Forbes, Iason A. Sofos et al. (+2 more)
We implement a
chiral spin-chain black hole simulator on IBM superconducting
quantum hardware and probe, within a common microscopic framework, both semiclassical horizon physics and interacting
quantum scrambling. We first measure the dispersion relation across the exterior, horizon and over-tilted interior regimes, reproducing the predicted
evolution of the effective light-cone structure. To probe Hawking thermality, we prepare a localised excitation inside the horizon and monitor its density response at an exterior site, observing the predicted inverse relation between the peak arrival time and the surface
gravity, thereby establishing a calibrated dynamical
estimator of the Hawking temperature. Beyond the semiclassical regime, we continuously tune the interactions and distinguish non-exponential operator spreading in the free-
fermion limit from Lyapunov-like OTOC decay in the strongly interacting
chiral regime. These measurements use observable-specific Floquet
circuits derived from the same parent
chiral model, including its mean-field and coordinate-equivalent XY descriptions, to reduce
circuit depth while preserving the physics relevant to each probe. Our results provide a unified programmable platform for studying horizon geometry, Hawking thermality and interacting scrambling on
quantum hardware.
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All authors Ryan Smith, Ewan Forbes, Iason A. Sofos, Andrew Hallam, Jiannis K. Pachos
Statistical Mechanics · Cross-listed from quant-ph
Thermal Throttling of Quantum State Transfer
Twesh Upadhyaya, T. C. Mooney, Yifan Hong et al. (+1 more)
Quantum state transfer on
qubit lattices is a crucial step in a panoply of
quantum information processing tasks. Understanding its fundamental limits in the presence of practical imperfections remains a pressing open question. In particular, it is unclear how thermal noise in the intermediate ancilla sites impedes transfer. In this work, we derive tight lower bounds on the necessary growth of commutator norms to achieve approximate state transfer. Specializing to 1D power-law systems with thermal ancilla states, we demonstrate that state transfer runtimes depend sensitively on the scaling of temperature with system size, improving logarithmic bounds to algebraic ones. Our work extends previous results on exact state transfer to the qualitatively different and more practically relevant regime of approximate state transfer.
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All authors Twesh Upadhyaya, T. C. Mooney, Yifan Hong, Alexey V. Gorshkov
Strongly Correlated Electrons
Junyi Cao, Ramanjit Sohal, Angela Kou et al. (+1 more)
Fractional
quantum Hall-
superconductor (FQH-SC)
heterostructures are predicted to host defect-bound parafermion zero modes (PZMs). We propose two related configurations to probe their fusion structure. In a Josephson junction coupled to a single
quantum point contact (QPC), quasiparticle tunneling switches the defect fusion channel, producing
stochastic transitions between branches of the fractional Josephson spectrum.
Embedding the junction in a two-QPC Fabry-Pérot interferometer provides a complementary probe. Weak zero mode tunneling produces fusion-channel-dependent interference while strong tunneling makes the interferometer probe a superposition of fusion channels and strongly suppresses the signal: in the topological limit it vanishes exactly, revealing the defects' non-Abelian nature even when the parent FQH state is Abelian.
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All authors Junyi Cao, Ramanjit Sohal, Angela Kou, Eduardo Fradkin
Strongly Correlated Electrons · Cross-listed from quant-ph
Dissipation-enhanced scrambling in the SYK model coupled to a lossy cavity
Pietro Pelliconi, Bastien Lapierre and Shinsei Ryu
We study the Yukawa-Sachdev-Ye-Kitaev model, a disordered model of $N$ Majorana
fermions and $R=\gamma N$
bosons in which the
bosons are linearly coupled to independent realizations of SYK $p$-body interactions, in the presence of dissipation, modeled by a Lindblad master equation. Motivated by recent proposals for implementing SYK models in
quantum simulators, we focus on bosonic leakage at rate $\kappa$. Initializing the system in the steady state, we analyze the late-time fermionic relaxation rate and the Lyapunov exponent, solving the large-$N$ theory both numerically and for $p$ large, finding a rich landscape of dynamical behaviors. Most notably, the Lyapunov exponent remains positive for every value of $\kappa$ and, for $p>2$, can even grow as $\kappa$ increases. The QED case $p=2$, which lies between the fully chaotic regime $p>2$ and the integrable case $p=1$, exhibits special features. We also identify a critical value of the
boson-to-
fermion ratio $\gamma_c \approx 2/p^2$ separating distinct dynamical regimes.
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Statistical Mechanics · Cross-listed from hep-th
Holographic Local Operator Quenches with Conserved Momentum and Spin
Pawel Caputa, Pedro Castellini Grand, Justin R. David et al. (+1 more)
We investigate the
holographic dictionary relating point particles carrying longitudinal momentum or angular momentum in asymptotically AdS$_3$ spacetimes to suitably regulated, time-evolved states created by local primary operators in the dual two-dimensional conformal field theory (2D CFT). We find that asymmetric left/right Euclidean smearing of local operators produces states carrying momentum, and the corresponding bulk excitation is a particle with conserved momentum. We compute the energy density and
entanglement entropy in these states and in their dual back-reacted geometries, finding exact agreement between the CFT and
gravity descriptions. We further extend this correspondence to particles with intrinsic
spin, whose CFT duals are primary operators with unequal holomorphic and anti-holomorphic scaling dimensions. We again find a precise match between CFT and
holographic calculations of energy densities and
entanglement entropies. Finally, we explore applications of these setups beyond holography by deriving the
evolution of Rényi
entropies in 2D rational CFTs and introducing a new class of local
quantum quench protocols with conserved longitudinal or angular momentum.
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All authors Pawel Caputa, Pedro Castellini Grand, Justin R. David, Rahul Metya
Mesoscale and Nanoscale Physics
Extension of the Shockley-Queisser Limit for Nanostructured Solar Cells
Rivo Herivola Manjakamanana Ravelonjato, Jean Patrice Rakotoniaina, Ravo Tokiniaina Ranaivoson et al. (+1 more)
This article extends the Shockley-Queisser limit to nanostructured
solar cells using the
quantum phase space formalism. The parameter B_ll represents the momentum variance in each confinement direction and acts as a variance-covariance
matrix linking the nanostructure geometry to thermodynamic properties. Electron-electron interactions are included via an exchange-correlation energy with an adjustable coefficient theta. The authors derive an analytical expression for the maximum efficiency as a function of size, shape, temperature, and doping. For the cylindrical geometry, the exact confinement energy uses the first zero of the Bessel function j_0,1. Numerical simulations are performed with Python 3.8.1, NumPy, and Matplotlib for PbS
quantum dots in four geometries: cube, square parallelepiped, cylinder, and sphere. The integral is evaluated using an exact convergent series expansion. Results show that the maximum efficiency reaches 48.7 percent for a 5 nanometre cube, 49.0 percent for flattened parallelepiped and cylinder shapes, and 49.1 percent for a 3 nanometre sphere. These values greatly exceed the bulk PbS efficiency of 15.8 percent and surpass classical Shockley-Queisser limits. For constant-volume shapes, two efficiency peaks appear corresponding to different aspect ratios. The model correctly returns to classical values for large sizes. This approach provides a theoretical framework for optimising nanostructured
solar cells and demonstrates that
quantum confinement offers a promising route to surpass traditional photovoltaic limits.
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All authors Rivo Herivola Manjakamanana Ravelonjato, Jean Patrice Rakotoniaina, Ravo Tokiniaina Ranaivoson, Wilfrid Chrysante Solofoarisina
Materials Science
Multi-Tool Robotics Enables In-Situ Sample Manipulation for Time-Resolved Synchrotron Measurements
Aditya Bondada, Elizabeth M. Wall, Eric Yuan Xiao et al. (+4 more)
The high
photon flux at synchrotron beamlines allows for the measurement of fast dynamical processes. However, beamline radiation-safety protocols prohibit human intervention during X-ray experiments, limiting the ability to perform versatile real-time sample manipulations during continuous data acquisition. Here we present a robotic platform at an X-ray scattering beamline to enable real-time sample handling and processing in the experimental hutch, revealing previously inaccessible transient in-situ dynamics in perovskite thin films. This modular multi-tool robotic architecture enables in-hutch sample manipulation beyond human-access constraints, establishing a foundation for automated and autonomous synchrotron experimentation.
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All authors Aditya Bondada, Elizabeth M. Wall, Eric Yuan Xiao, Quinn C. Burlingame, Yueh-Lin Loo, Esther H. R. Tsai, Ruipeng Li
Strongly Correlated Electrons
Unconventional bond- and current-density waves on hexagonal lattices
Andras Szabo, Hannes Braun and Laura Classen
Charge-density wave (CDW) orders are conventionally described as modulations of on-site charge at an ordering wave vector $\boldsymbol{Q}$ with
symmetry-related wave vectors typically forming a multicomponent order-parameter
manifold. Recent developments significantly broadened this phenomenology to bond and loop-current density waves, which possess nontrivial, potentially
symmetry-breaking textures within the unit
cell in addition to their spatial modulation at $\boldsymbol{Q}$. Such textures arise from particle-hole condensates with nonzero angular momentum, analogous to unconventional superconductivity, and their
symmetries are described by the little group $G_{\boldsymbol{Q}}$. In this work, we develop a framework for unconventional CDW phases that simultaneously incorporates the local
symmetries described by little group and the presence of multiple
symmetry-related ordering wave vectors, also known as the
star. The resulting multicomponent order parameter transforms under representations of the full space group induced from irreducible representations of $G_{\boldsymbol{Q}}$. We apply this framework to two-dimensional
lattices with sixfold
symmetry and ordering wave vectors along high-
symmetry lines, and derive the corresponding Landau free energies. As a microscopic example, we demonstrate the emergence of unconventional bond and loop-current orders from electronic interactions on the triangular
lattice within the random phase approximation, and determine their ground states by microscopically evaluating the relevant coefficients in the free energy. Our framework provides a systematic route to describing unconventional modulated phases and can be readily extended to more complex
lattices.
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Quantum Gases
Electrostriction in a Bose-Einstein Condensate of Dipolar Molecules
Haneul Kwak, Ian Stevenson, Weijun Yuan et al. (+5 more)
The recent creation of a Bose-Einstein condensate (BEC) of dipolar molecules has opened a new frontier for many-body
quantum systems in which dipolar interactions can drive novel self-organization phenomena. Here, we observe electrostriction in a molecular BEC, an elliptical deformation driven by anisotropic dipolar interactions. We use double microwave dressing, involving $\sigma$- and $\pi$-polarized fields, to control non-axially symmetric dipolar interactions. We compare the experimental observations of electrostriction to a model based on an extended Gross-Pitaevskii equation and find excellent agreement in the regime of weak to moderate interactions. Using electrostriction, we demonstrate that the molecular BEC can be torqued by dynamically changing the orientation of the elliptical $\sigma$ microwave field. This provides a route to setting molecular
quantum gases into rotation, opening opportunities to probe vorticity, superfluidity, and supersolidity in strongly dipolar matter.
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All authors Haneul Kwak, Ian Stevenson, Weijun Yuan, Siwei Zhang, Asaf Toprakci, Lin Su, Tijs Karman, Sebastian Will
Strongly Correlated Electrons
Chiral bosonic mean-field Ansatz and spin dynamics in spin-1 Kitaev magnets
Daiki Sasamoto, Arnaud Ralko, Jaime Merino et al. (+1 more)
The Kitaev model is a paradigmatic system for realizing
quantum spin liquids, but its higher-
spin extensions are not exactly solvable, and their
spin dynamics is less well understood than in the
spin-1/2 case. In this work, we reexamine a previously introduced triplet-pairing $\phi_t = \pi/2$ phase pattern for the
antiferromagnetic $S = 1$ Kitaev model and extend the analysis to weak symmetric off-diagonal exchanges $\Gamma$ and $\Gamma'$. Using a bond-operator formulation of Schwinger-
boson mean-field theory, we calculate the dynamical
spin structure factor for the triplet 0-flux and triplet $\pi/2$-flux Ansätze with a
spin-correlation scheme appropriate for Kitaev interactions. In the pure Kitaev limit, the $\pi/2$-flux Ansatz yields a flatter spectrum than the 0-flux Ansatz. The real-space
spin correlations show that the $\pi/2$-flux Ansatz suppresses longer-distance correlations more strongly than the 0-flux Ansatz, yielding a correlation pattern closer to the short-ranged form expected in the Kitaev limit. This comparison shows that the flatness of $S(\boldsymbol{q}, \omega)$ is tied to short-ranged
spin correlations and is therefore an important consistency check, although it is not, by itself, a diagnostic of time-reversal-
symmetry breaking. We then study weak off-diagonal exchanges along $\Gamma' = \Gamma$ near the pure Kitaev limit, taking the same-sign relation from analyses of candidate
spin-1 Kitaev materials. Gapped solutions are obtained within the constrained $\pi/2$-flux
manifold, and the spectra share the qualitative energy- and momentum-space features found by finite-size exact diagonalization. Taken together, these results support the triplet $\pi/2$-flux
chiral bosonic Ansatz as a useful mean-field description of
spin dynamics near the
antiferromagnetic $S = 1$ Kitaev limit with weak off-diagonal exchanges.
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All authors Daiki Sasamoto, Arnaud Ralko, Jaime Merino, Joji Nasu
Materials Science
Avalanche-like Plasticity in Complex Concentrated Alloys: A Review Across Scales
Michal Knapek, Tomáš Tayari, Kristián Máthis et al. (+1 more)
Complex concentrated
alloys (CCAs), including high- and medium-
entropy alloys, deform in chemically heterogeneous energy landscapes where dislocation glide, solute aging, twinning, phase transformation and microstructural barriers may all contribute. This review discusses avalanche-like and serrated plasticity in CCAs across scales. The first part separates the relevant length scales and methods used to access them. At microscopic and mesoscopic scales, acoustic emission (AE) and microcompression studies reveal discrete dislocation avalanches and strain bursts that may be hidden in conventional macroscopic curves. At the specimen scale, local extensometry and digital image correlation (DIC) studies of the Portevin-Le Chatelier effect show how collective defect dynamics can organize into deformation bands and macroscopic stress serrations. Together, these approaches show that plastic flow may appear smooth only as an average response, while remaining intermittent at finer scales. The second part reviews direct CCA evidence, with emphasis on AE, stress-serration statistics, microplasticity, DIC, nanoindentation and small-scale deformation. A central conclusion is that serrated flow in CCAs should not be treated as a single phenomenon. Depending on chemistry, temperature, strain rate and microstructure, it may originate from dynamic strain aging, twinning, martensitic transformation, slip localization, or a combination of these mechanisms. Reported power-law-like distributions and exponents partly overlap with those known from simpler
crystals and
alloys, and the present evidence does not establish a distinct CCA-specific universality class. CCAs are therefore best viewed as tunable systems in which chemical disorder, short range order, phase stability and microstructure can modify the nucleation, arrest and synchronization of collective plastic events.
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All authors Michal Knapek, Tomáš Tayari, Kristián Máthis, Miloš Janeček
Materials Science · Cross-listed from cs.LG
Enhancing EBSD throughput of battery electrode materials using super-resolution generative adversarial networks
John Mangum, Andrew Glaws, Francois Usseglio-Viretta et al. (+2 more)
Quantitative microstructural characterization of Li-ion battery electrode materials using electron backscatter diffraction (EBSD) has been proven as a critical method for optimizing
cell performance. However, the inherently slow nature of EBSD can hinder the throughput of analyses needed for statistical representation of a material microstructure being developed. This work demonstrates a machine learning super-resolution framework using a generative
adversarial network (SRGAN) to significantly increase EBSD throughput. The SRGAN model was trained on EBSD data of LiNixMnyCozO2 (NMC) cathode particles to computationally enhance low-resolution
datasets and its performance is compared against classical interpolation methods across various upscaling factors (2x to 12x). Both qualitative image metrics and quantitative microstructural analysis verified that the SRGAN systematically outperformed classical methods, particularly in preserving small grains and maintaining realistic grain boundaries. We demonstrate that a 5x upscaling factor, corresponding to a 25x speed-up in acquisition time or a 25x larger field of view, is practical while maintaining acceptable accuracy in key metrics like grain size and shape. For instance, at 5x upscaling, relative errors were +5.7%, +8.2%, and -14.6% on grain area-equivalent diameter, grain maximum sphere-inscribed diameter, and grain boundary length, respectively. The SRGAN methodology developed in this work significantly enhances the efficiency of EBSD acquisition for more statistically robust microstructural
dataset, enabling EBSD as a high-throughput characterization tool for materials research and industrial process development.
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All authors John Mangum, Andrew Glaws, Francois Usseglio-Viretta, Steven Spurgeon, Donal Finegan
Materials Science
JANUS: A Multi-modal Foundation Neural Sampler for Disordered Materials
Denis Blessing, Mouyang Cheng, Maximilian Schebek et al. (+4 more)
Many problems in disordered materials require sampling beyond fixed composition and volume, where coupled changes in atomic identities and structure create a prohibitively expensive discrete-continuous sampling problem. Here we introduce JANUS, a
multimodal neural sampler that couples continuous and masked discrete
diffusion through an equivariant graph neural network trained directly from energy evaluations, without pre-generated
equilibrium data. In
benchmark Ising and isobaric $\Delta\mu NPT$
alloy systems, JANUS reproduces reference Monte Carlo
equilibrium observables and recovers free energies and phase behavior with more than three orders of magnitude fewer energy evaluations. In multicomponent
alloys, JANUS enables conditional steering toward prescribed chemical short-range order and enhanced bulk modulus and, when coupled to a large
language model evolutionary
agent, performs efficient inverse design for balanced optical and mechanical properties. In
semiconductors like silicon and diamond, JANUS explores vacancies and dopants spanning 15 elements in grand-canonical $\mu VT$ ensembles, recovers established defects including the silicon $E$ centre, and identifies new candidate defect pairs and triplets for
quantum engineering, including S-Ti in silicon and B-O-O in diamond, with deep in-gap states validated by hybrid-functional density functional theory. By unifying discrete site identities with continuous structural and volumetric relaxation, JANUS provides a foundation for thermodynamic sampling, characterization and inverse design of chemically disordered materials.
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All authors Denis Blessing, Mouyang Cheng, Maximilian Schebek, Jutta Rogal, Mingda Li, Carles Domingo-Enrich, Yuanqi Du
Mesoscale and Nanoscale Physics
Ultra-low energy (20 - 300 eV) electron imaging and diffraction
Tatiana Latychevskaia
The lecture discusses the properties of low-energy electrons compared to the electrons of conventional energies employed in commercial transmission electron microscopes. Low-energy electron diffraction and low-energy electron holography principles and experimental schemes are presented and discussed.
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Materials Science
Local Structure and Dynamics of Three-Dimensional Covalent Organic Frameworks
Francesco Tavani, Saber Mirzaei, Jian Yin et al. (+6 more)
Resolving and controlling the local dynamical properties of covalent organic frameworks (COFs) remains a central challenge, particularly when assembled from large, flexible building units. Here, we combine synchrotron X-ray pair distribution function (PDF) analyses with machine learning-accelerated molecular dynamics (MD) simulations to resolve the local structure and dynamics of two three-dimensional imine-linked COFs, COF-682 {[(DHP)(TAM)]$_{imine}$}, assembled from 6,13-dihydropentacene (DHP) and tetrakis(4-aminophenyl)methane (TAM), and COF-612 {[(HBC-LA$_{12}$)(HAPT)$_2$]$_{imine}$}, assembled from nanographene dodecabenzaldehyde hexakis{[3,5-bis($p$-formylphenyl)-4,6-dimethoxyphenyl]}hexabenzocoronene (HBC-LA$_{12}$) and 2,3,6,7,14,15-hexa(4-aminophenyl)triptycene (HAPT). Validated against the experimental PDFs through ensemble-averaged calculations, the simulations show that the exposed $\pi$-surface and V-shaped geometry of the DHP linker endow COF-682 with enhanced local flexibility through face-to-face and offset $\pi$-stacking interactions differing in both their average interplanar separation and their ring-plane tilt angle. In contrast, the extended nanographene linker rigidifies COF-612 by maintaining the planarity of its fused cores, while the linker pendant aryl rings equip both COFs with enhanced librational ability. The simulations further provide quantitative measures of the translational and reorientational mobility of the linkers, revealing how local COF dynamics may be tuned by balancing non-covalent interactions and different degrees of aromatic
rigidity. The PDF-MD experimental-computational approach holds promise as a general method beyond conventional crystallography to gain insights into the local properties of COFs with the aim of directing their dynamic function.
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All authors Francesco Tavani, Saber Mirzaei, Jian Yin, Yen-hsu Lin, Caden Myers, Cheng-Hung Lin, A. M. Milinda Abeykoon, Simon J. L. Billinge, Omar M. Yaghi
Superconductivity
Large Field-Free Superconducting Diode Effect with Nonmonotonic Polarity Reversals in NbSe$_2$/CrBr$_3$ Heterostructures
Shengbiao Sun, Lang Xiao, Chenghao Shen et al. (+10 more)
The superconducting diode effect (SDE), characterized by nonreciprocal dissipationless supercurrent, offers a promising route toward ultralow-power superconducting electronics. Yet most realizations require an external
magnetic field, and achieving a large, controllable SDE at zero field remains challenging. Here we report a field-free SDE with an efficiency reaching 35.7% in a van der Waals NbSe$_2$/CrBr$_3$
heterostructure, whose polarity is programmable by
magnetic-field history. Unlike conventional mechanisms based on finite-momentum pairing, the SDE originates from the leading
symmetry-allowed cubic term odd in Cooper-pair momentum, which yields unequal critical currents while leaving the
equilibrium condensate at zero momentum. Remarkably, upon sweeping a perpendicular
magnetic field, the diode polarity undergoes nonmonotonic and hysteretic reversals that cannot be explained by Meissner screening or conventional
ferromagnetic proximity. Combining transport measurements, micromagnetic simulations, and a generalized Ginzbur-Landau theory, we attribute these unconventional behaviors to layered ferrimagnetism in CrBr$_3$, where coexisting
ferromagnetic and
antiferromagnetic interlayer couplings produce a history-dependent interfacial exchange field acting on NbSe$_2$. Our results reveal a distinct mechanism for nonreciprocal superconductivity and establish layered van der Waals magnetism as a versatile platform for high-efficiency, programmable, field-free superconducting diodes.
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All authors Shengbiao Sun, Lang Xiao, Chenghao Shen, Bowen Hao, Jia-Peng Peng, Ziye Zhu, Feiyue Wang, Qilin Han, Ya-Qing Bie, Shuo Wang, Tong Zhou, Dapeng Yu, Ben-Chuan Lin
Superconductivity
Ultrasonic attenuation in inhomogeneous superconductors
Aman Sardwal, Andreas Kreisel and Shantanu Mukherjee
Subgap bound states can produce pronounced features in the density of states without necessarily giving rise to a corresponding signal in ultrasonic attenuation. We show that the coherence factors act as a filter for the contribution of bound states to ultrasonic attenuation. In a phase-biased
superconductor–normal–
superconductor junction, the Andreev bound states produce a resonance in the attenuation when the
phonon frequency matches the phase-dependent separation between the subgap levels. The situation is different at a $(110)$ grain boundary in a $d_{x^2-y^2}$
superconductor. There, nonmagnetic
impurity-induced bound states remain weak in the attenuation despite their large spectral weight, because the relevant coherence factors nearly cancel. When local magnetism develops near the boundary, this cancellation is removed, the bound states become
spin split, and a clear attenuation peak appears, which we argue is governed by a process involving emission of
phonons by pair of quasiparticles at low temperatures. We obtain these results using a real-space Bogoliubov–de Gennes formulation of ultrasonic attenuation and
benchmark the method against the known low-temperature behavior of homogeneous $s$- and $d$-wave
superconductors. The results show that ultrasound can distinguish bound states with similar spectral signatures but different
symmetry and
spin structure.
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Strongly Correlated Electrons · Cross-listed from math.AG
Equations of Tree Tensor Network Varieties
Serkan Hoşten, Niharika Chakrabarty Paul, Otto T. P. Schmidt et al. (+1 more)
We show that tree tensor network varieties, including tensor train varieties, are general Markov models associated to spaced trees. This allows us to prove that the
prime ideals of these varieties are generated by minors of
matrix flattenings. In the case of tensor train varieties, we discuss whether these minors form a Gröbner basis and provide a combinatorial method to compute the degree for order $3$ tensor trains.
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All authors Serkan Hoşten, Niharika Chakrabarty Paul, Otto T. P. Schmidt, Dmitry Skurt
Other Condensed Matter · Cross-listed from quant-ph
Distinct Modes of Quantum Information Transfer in Power-Law Long-Range Spin Networks
E.E. Marshall, C.C. Nelmes, T.J.G. Apollaro et al. (+2 more)
We identify different regimes of
quantum state transfer in long-range coupled
spin-$\frac{1}{2}$ systems, where naturally occurring power-law interactions enable rapid, high-fidelity transfer with minimal engineering. Across a broad range of interaction profiles, from effectively nearest-neighbour coupling to Coulomb interactions, we show how long-range connectivity fundamentally reshapes the mechanisms underlying information propagation within such systems. For effectively short-range interactions, transfer follows familiar ballistic transfer dynamics: an initially localised excitation spreads across many eigenmodes concentrated within the approximately linear region of the spectrum, enabling robust wavepacket motion. In contrast, increasing long-distance interactions via lowering the power-law exponent $\alpha$ ($\alpha=1-2$) drives a striking transformation, where the initial state becomes confined to progressively fewer eigenmodes, ultimately reducing the dynamics to the coherent participation of only a few states corresponding to the highest eigenenergies. This spectral localization gives rise to emergent long-range oscillations between distant sites, revealing a distinct – and faster – transfer mechanism arising from the intrinsic structure of long-range
quantum interactions rather than from full-system engineering pathways.
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All authors E.E. Marshall, C.C. Nelmes, T.J.G. Apollaro, T.P. Spiller, I. D'Amico
Materials Science
Anti-spin Laue groups: classification of anti-altermagnets and their representative minimal models
Colin Lange, Rodrigo Jaeschke-Ubiergo, Alexander Mook et al. (+1 more)
Anti-altermagnets exhibit odd-parity nonrelativistic
spin splitting, yet unlike even-parity altermagnets, their momentum-space
symmetries lack a reduced classification analogous to
spin Laue groups. Here, we introduce anti-
spin Laue groups, organized into three distinct classes, and identify 21 groups describing the odd-parity partial wave character of this unconventional class. Together with the 10
spin Laue groups of altermagnets, they complete the classification of nonrelativistic unconventional magnets with collinear momentum-space
spin polarization. Anti-
spin Laue groups also provide a many-to-one reduction of
spin space (point) groups by retaining only their action on the collinear momentum-space
spin polarization, thereby directly encoding the
symmetry-enforced nodal
spin-splitting character. Based on this we develop a systematic model-construction
algorithm yielding minimal, material-oriented four-band models. This framework places odd- and even-parity unconventional magnets on equal footing within a unified momentum-space
symmetry description.
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All authors Colin Lange, Rodrigo Jaeschke-Ubiergo, Alexander Mook, Jairo Sinova
Materials Science
Ab initio-based Deep-Learning Prediction of Carrier Mobility in Strongly Anharmonic Materials
Juan Zhang, Boheng Zhao, Yang Li et al. (+4 more)
Predicting charge transport in strongly anharmonic materials, particularly ultralow thermal conductors, remains a major challenge for first-principles methods. In such systems, perturbative treatments of electron-
phonon interactions and the harmonic
phonon picture often break down, necessitating non-perturbative approaches. The ab initio Kubo-Greenwood(aiKG) formalism provides a rigorous framework for evaluating temperature-dependent carrier transport beyond the harmonic approximation. Nevertheless, its practical application is computationally demanding because it requires large supercells, extensive statistical sampling, and extrapolation to the zero-frequency limit. In this work, we introduce an artificial-intelligence(AI)-assisted aiKG framework that incorporates the deep-learning
Hamiltonian model. By predicting the Kohn-Sham
Hamiltonian with sub-meV accuracy for supercells of up to 250 atoms, the model bypasses the costly iterative self-consistent field calculations while retaining first-principles reliability within the scope of effects captured by the training data. Using a strongly anharmonic thermal
insulator, potassium iodide(KI) as a
benchmark system, we demonstrate that the proposed approach enables efficient simulations of electronic structure and transport properties from a large supercell. The framework reproduces temperature-dependent carrier mobilities, spectral functions, and effective masses in close agreement with the underlying density functional theory while reducing computational cost to 10%. These results suggest that the AI-assisted aiKG framework can make non-perturbative transport calculations tractable for strongly anharmonic materials, opening a scalable route towards realistic simulations and accelerated discovery of new functional materials.
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All authors Juan Zhang, Boheng Zhao, Yang Li, Yong Xu, Hao Zhang, Kisung Kang, Matthias Scheffler
Superconductivity
Emergent BEC mechanism in flat-band superconductors
V. Berger, I.S. Tupitsyn, B. Currie et al. (+3 more)
The formation of bound bosonic pairs of
fermions, followed by their Bose-Einstein (quasi) condensation (BEC), is a foundational mechanism of superconductivity. At low filling, flat-band superconductivity is well captured by this mechanism provided the flat band is separated from the occupied lower band by an energy gap. However, particularly high $T_c$ values are anticipated when the non-interacting flat and lower bands touch—as in the prototypical attractive Lieb-
lattice model studied here—invalidating the conventional picture: while interactions might protect the bound state by opening a gap, no small parameter guarantees the separation of the bound-state energy from this gap or occupied-band excitations, leaving the pair's fate uncertain. Based on a controlled-precision numerical protocol—which we demonstrate to be essential in this fundamentally non-perturbative problem—we show that the BEC mechanism, underpinned by an interaction-induced gap, is generically robust and remarkably efficient:
fermions doped into the flat band form bound pairs within this gap with an anomalously light effective mass, enabling an exceptionally high $T_c$.
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All authors V. Berger, I.S. Tupitsyn, B. Currie, B.V. Svistunov, E. Kozik, N.V. Prokof'ev
Materials Science · Cross-listed from physics.chem-ph
Universal Machine-learning Molecular Dynamics at the Speed of Empirical Potentials
Tiancheng Li, Jianming Xue, Linfeng Zhang et al. (+2 more)
No interatomic potential has offered universality across chemistry, near-first-principles accuracy and the speed of empirical potentials at once. Here we introduce DPA4C, an equivariant potential whose architecture and compressed CUDA operators are co-designed under deployment constraints to pursue accuracy and efficiency together. Five variants spanning a 49-fold parameter range form the high-throughput end of the measured accuracy–throughput frontier. The largest variant approaches the accuracy of the MACE-Omat models at about two orders of magnitude higher measured throughput. The most compact reduces the energy, force and stress errors of the fastest existing universal MLIP by 61.4%, 48.1% and 34.3% at 1.92 times its saturated throughput. All five variants complete multimillion-atom simulations on a single GPU and run molecular dynamics for 2.048 billion atoms on 1,024 16-GB NVIDIA V100 GPUs at 83.3–91.2% weak-scaling efficiency. Compared with the MEAM empirical potential, DPA4C-Nano reaches 1.8 and 2.5 times the saturated throughput in single-GPU scans on the same V100 hardware for diamond carbon and FCC copper, respectively. DPA4C therefore brings
quantum-trained universal accuracy into a regime of speed and system size previously associated with empirical potentials.
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All authors Tiancheng Li, Jianming Xue, Linfeng Zhang, Duo Zhang, Han Wang
Disordered Systems and Neural Networks · Cross-listed from physics.chem-ph
Molecular Implementation of the Machine-Learned Skala Exchange-Correlation Functional in CP2K through GauXC
Franz Pöschel, Johann Pototschnig, Frederick Stein et al. (+6 more)
Machine-learned exchange–correlation (XC) functionals offer a route to improve Kohn–Sham density-functional theory without incurring the cost of explicitly correlated electronic-structure methods. Their use in production simulation codes, however, requires a well-defined mapping between the learned model and the host-code density representation. We formulate and implement a Skala-1.1 interface in CP2K through the external GauXC library. CP2K supplies the geometry, Gaussian basis,
spin-resolved atomic-orbital density
matrix, and communicator, while GauXC evaluates the XC energy, atomic-orbital potential
matrix, and available
nuclear derivatives. The interface accepts both all-electron and valence-only density
matrices. The latter may arise from separable dual-space pseudopotentials or molecular effective-core potentials. Implementation errors are isolated from functional differences by comparing the Perdew–Burke–Ernzerhof (PBE) functional evaluated through GauXC with native CP2K PBE. The resulting interface gives consistent energies, forces validated against finite-difference total-energy checks, and force-based molecular-virial diagnostics for representative molecular cases. The dietGMTKN55
benchmark suite is evaluated with an all-electron Gaussian augmented plane-wave treatment for elements up to bromine and def2 effective-core potentials for the heavier elements. The resulting aggregate mean absolute deviation of 1.255 kcal/mol is within 0.012 kcal/mol of the corresponding Skala reference value of 1.243 kcal/mol. This work establishes a validated molecular implementation of Skala in CP2K through GauXC.
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All authors Franz Pöschel, Johann Pototschnig, Frederick Stein, Andreas Knüpfer, Thijs Vogels, Stefano Battaglia, Sebastian Ehlert, Jürg Hutter, Thomas D. Kühne
Materials Science
The role of weak interfaces in the tensile deformation and fracture of particle-filled polymers studied by phase-field model
Xu Chen, Ya Duan, Xiaoying Zhuang et al. (+1 more)
Weak particle-
matrix interfaces play a critical role in the tensile fracture of particle-filled
polymer composites, but how they govern progressive debonding, fracture localization, and the resulting changes in macroscopic mechanical properties remains insufficiently understood. In this study, a cohesive-zone phase-field model incorporating a hyperelastic
polymer matrix and a smeared interface is employed to investigate the coupled
evolution of interfacial debonding and
matrix fracture in particle-filled
polymer composites. The model is calibrated against and compared with uniaxial tensile responses of particle-filled polyurethane composites and then used to study how interfacial strength, interfacial fracture energy, and
matrix fracture properties affect the macroscopic stress-strain response and damage
evolution. The results show that weak interfaces can induce an intermediate softening regime in the stress-strain response, characterized by a reduced effective tangent stiffness and associated with distributed interfacial damage. Interfacial strength mainly controls the initiation of debonding, whereas interfacial fracture energy affects whether debonding can develop progressively in a distributed manner or rapidly localizes into a dominant crack band. Comparisons with well-bonded reference systems further demonstrate that weak interfaces may reduce the maximum stress but increase the strain at break by promoting distributed debonding around particles and delaying the formation of a dominant crack band. These findings clarify the dual role of weak interfaces and provide a mechanistic understanding of interface-controlled tensile failure in particle-filled
polymer composites.
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All authors Xu Chen, Ya Duan, Xiaoying Zhuang, Timon Rabczuk
Strongly Correlated Electrons
Sign-problem-resilient singular-value probe in determinant quantum Monte Carlo
Wen Chen and Rubem Mondaini
The sign problem limits determinant
quantum Monte Carlo studies of strongly correlated
fermion systems. In the
spin-channel Hubbard-Stratonovich decoupling,
spin correlations are exactly related to auxiliary-field correlations. This relation implies that an
antiferromagnetic transition reorganizes auxiliary-field configurations and thereby changes the statistical structure of the resulting
fermion matrices. We use the adjacent gap ratio of low-lying singular values of the space-time
fermion matrix to probe interaction-driven transitions in two half-filled honeycomb-
lattice Hubbard models. In the sign-free honeycomb Hubbard model, the statistic tracks the established transition from a Dirac semimetal to an
antiferromagnetic Mott
insulator. In the complex-weight Haldane-Hubbard model, the transition-sensitive feature remains visible in the phase-quenched reference ensemble and occurs near previous estimates of the transition. Moreover, phase reweighting only weakly modifies the gap ratio over the regimes investigated, despite the rapid suppression of the average phase. These results establish singular-value statistics as a sign-problem-resilient probe of interaction-driven transitions in determinant
quantum Monte Carlo.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Interface Capacity and Architectural Replenishment Determine Entanglement-Generation Speed in Quantum Networks
Shi-Ju Ran
We show that
entanglement-generation speed across a fixed network interface is governed by two distinct resources: the entangling capacity of the interface itself and the ability of the surrounding architecture to replenish it with fresh degrees of freedom. For fermionic Gaussian dynamics, we derive the coefficient-sharp bound $\sum_k|\dot\theta_k|\leq\frac12\|K_{AB}\|_*$ on the collective speed of the canonical
entanglement angles. Explicit Ising-chain rematching trajectories saturate this bound, thereby certifying exact minimum interaction times under the stated control model. Beyond the Gaussian setting, exhaustive optimization of the complete $N=8$ tree–tree family shows that, at fixed interface capacity, first-layer
entanglement, connectedness, and edge budget, the saturation depth is exactly classified by rooted architecture. With higher-resolution $x$-only control, variational
entanglement-enhancing-field (VEEF) optimization reaches the numerically resolved fast-$X$ optimum in a two-channel
benchmark. Across all 21
symmetry-reduced rooted orbits, a pre-specified two-time VEEF growth diagnostic recovers the complete replenishment partition directly from optimized dynamics. Interface capacity therefore sets how much entangling flux is available, whereas architecture determines whether fresh degrees of freedom can continually replenish the interface and sustain repeated use of that capacity.
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Statistical Mechanics · Cross-listed from quant-ph
Subsystem Symmetries and Fracton Models in Quantum Error Correction
Giovanni Canossa
Constructing new
quantum codes and understanding their error resilience are central challenges in the development of robust
quantum memories. Topological codes are particularly promising due to their favorable error-correcting properties and their connections to phases of matter in many-body physics. In this thesis, we explore the interplay between classical Ising models and
quantum error correction through subsystem
symmetries, fracton topological order, and Kramers-Wannier-type duality. We study two three-dimensional classical self-dual Ising models with subsystem
symmetries, the Tetrahedral Ising model and the Fractal Ising model, investigating their thermal behavior, their relation to fracton phases through subsystem-
symmetry gauging, and the properties of the resulting fracton codes. Using a statistical-mechanical mapping, we determine the optimal code-capacity threshold of the Checkerboard code to be $0.107(3)$, which saturates the theoretical limit for CSS codes and represents the highest optimal error threshold among known three-dimensional codes. We relate this saturation to a generalized
entropy relation for classical
spin models satisfying a Kramers-Wannier-type duality, and argue how this prediction extends to CSS codes with zero encoding rate whose $X$- and $Z$-noise models map to classically dual
spin models. These findings establish fracton codes as highly resilient candidates for
quantum memories and demonstrate the power of the statistical-mechanical framework, together with its duality predictions, in analyzing and constructing robust
quantum error-correcting codes.
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