Strongly Correlated Electrons
Effective band-projected description of interacting quasiperiodic systems
Flavio Riche, Raul Liquito, Bruno Amorim et al. (+3 more)
We study the interplay between electronic interactions and quasiperiodicity in a one-dimensional narrow-band system, focusing on ground-state and low-energy excitation properties. Using band projection as low-energy effective approach, we show that a projection restricted to first order in the interaction strength fails to reproduce the correlated phase diagram. This contrasts with the standard success of first-order band projection in translationally invariant flatband systems and highlights the essential role of virtual processes involving remote bands in quasiperiodic settings. By incorporating second-order interband contributions perturbatively, we obtain an effective
Hamiltonian that quantitatively reproduces the exact phase iagram previously obtained using density
matrix renormalization group calculations, including the transition between a Luttinger
liquid and a charge-density-wave phase and the crossover to a quasifractal charge-density-wave regime at strong quasiperiodicity. We further use this controlled framework to investigate low-energy neutral excitations and the optical conductivity, identifying clear dynamical signatures distinguishing the different phases. Our results establish second-order band projection as a reliable tool for correlated quasiperiodic narrow-band systems and suggest a promising route for studying interacting quasiperiodic and moiré materials beyond one dimension.
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All authors Flavio Riche, Raul Liquito, Bruno Amorim, Eduardo V. Castro, Pedro Ribeiro, Miguel Gonçalves
Other Condensed Matter · Cross-listed from gr-qc
Topological Phase Transitions in Superfluids Near Black Hole Horizons
Cristian R. Ghezzi and Paulo S. Custodio
We investigated a two-dimensional superfluid model immersed in a black hole spacetime and hypothesize that if a black hole collides with a thin superfluid film, it will trigger a topological phase transition within the superfluid, characterized by the production of
vortex–antivortex pairs. We adapted the 2D XY model to a curved spacetime and elucidated the topological phase transition in response to variations in the black hole's temperature. Specializing the model to a Schwarzschild–de Sitter black hole, we found a proliferation of
vortex–antivortex pairs close to the event and cosmological horizons.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Quantum Process Realization of LDPC Code Dualities and Product Constructions
Shuhan Zhang, Deepak Aryal and Yi-Zhuang You
We realize a broad class of code transformations, including Kramers-Wannier duality, tensor product, and check product, as
quantum processes consisting of ancilla initialization, local
unitaries, and projective measurements. Using ZX-calculus, we formulate these code transformations diagrammatically and develop a systematic
algorithm for extracting their
quantum-process realizations. Central to our framework is the observation that the physical content of a classical LDPC code is captured by the operator
algebra associated with its Tanner graph, and that code transformations correspond to maps between such
algebras. Kramers-Wannier duality then admits a natural interpretation as gauging, while tensor and check products correspond to coupled-layer constructions in which interlayer coupling and projection implement a quotient on stacked operator
algebras. Together, these results establish a unified framework connecting code transformations,
quantum circuits, and mappings between distinct
quantum phases of matter.
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Materials Science
Smoothed Boundary Method Framework for Electrochemical Simulation of Li-ion Battery Cathode with Complex Microstructure: Model, Formulation and Parameterization
Hui-Chia Yu, Bernardo Orvananos, Scott Cronin et al. (+3 more)
Rechargeable battery electrodes have highly complex microstructures, consisting of nonuniform electrode particles, tortuous electrolyte channels, and irregular particle-electrolyte interfaces. Moreover, the electrochemical processes involve several coupled physical mechanisms, including mass transport in the electrode particles and electrolyte, current continuity in the solid and
liquid, and electrochemical surface reactions. These
geometric and mechanistic complexities create a challenging barrier of electrochemical simulations at the microstructural level using conventional methods. In this paper, we introduce a smoothed-boundary method (SBM) electrochemical simulation framework for modeling the electrochemical dynamics of complex battery electrode microstructures. The conventional governing equations are reformulated into SBM versions, and are solved using uniform Cartesian grids. The simulations utilize an image-based, experimentally reconstructed 3D microstructure as the input geometry, and the physical parameters acquired from experimental measurements. Two models of lithiation mechanisms, solid-solution and two-phase, are examined under potentiostatic discharging of a Li$_x$CoO$_2$ composite cathode. Detailed dynamics of the complex cathode microstructure are revealed through the simulations. The comparison between the two models indicates that modeling two-phase lithiation with Fick's
diffusion will overestimate the electrode's performance. The presented simulation framework provides an innovative avenue in exploring the electrochemical dynamics at the microstructural level.
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All authors Hui-Chia Yu, Bernardo Orvananos, Scott Cronin, Martin Bazant, Scott Barnett, K. Thornton
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Perspective: Interactions and Nonlinearity in Non-Hermitian Physics
Federico Roccati and Federico Balducci
For decades, Hermiticity was considered an immutable axiom of
quantum mechanics, essential for ensuring real energies and
unitary evolution. This perspective has shifted radically, driven by the realization that non-Hermitian
Hamiltonians provide a powerful effective description of open
quantum systems, granting access to unique phenomena such as Exceptional Points and the Non-Hermitian Skin Effect. In this Perspective, we chart the trajectory of this field, moving from its established foundations in single-particle, linear models to the emerging frontier of interacting many-body systems. We first clarify the physical origins of non-Hermitian dynamics, distinguishing between mean-field approximations, conditional "no-click"
evolution, and exact Liouvillian dynamics. We then focus on the rich phenomenology arising from the interplay of non-Hermiticity and interactions. We discuss interaction-induced topological phases, the generalization of skin effects to the many-body
Hilbert space, and the distinct signatures of dissipative
quantum chaos and complexity. Finally, we highlight collective phenomena in nonlinear regimes, including skin
solitons and dissipative phase transitions. We also comment on measurement-induced
entanglement transitions and their relation to non-Hermitian spectra and
topology. By synthesizing these diverse developments, we provide a roadmap for the future of non-Hermitian physics.
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Mesoscale and Nanoscale Physics
Spin qubit gates via phonon buses in electron nanowires
Dylan Lewis, Roopayan Ghosh, Sanjeev Kumar et al. (+4 more)
Scalable architectures for
quantum computing using
semiconductor quantum dots require interactions between
qubits beyond adjacent
quantum dots. Here, we propose using nanowires of electrons to mediate the interaction between two
quantum dots. Virtual
phonons in the linear chain of electrons can mediate an interaction that gives rise to effective
spin-
spin coupling of the electrons in distant
quantum dots. We find coupling strengths of more than 30 MHz for experimentally realisable parameters in GaAs
quantum dots.
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All authors Dylan Lewis, Roopayan Ghosh, Sanjeev Kumar, Michael Pepper, Charles Smith, Karyn Le Hur, Sougato Bose
Mesoscale and Nanoscale Physics
Overcoming intrinsic material limitations through cavity feedback
M. Ebrahimi, Y. Huang, V.A.S.V. Bittencourt et al. (+3 more)
Magnons, the quanta of
spin waves, have significant potential for use in modern technologies, especially when strongly coupled to another mode for read-out and control. However, while
magnons strongly interact with microwave
photons via the
magnetic-dipole interaction to form hybrid cavity-
magnon polariton modes, the weak magnetostrictive
magnon-
phonon interaction, together with large polariton linewidths dominated by
magnon dissipation, has so far restricted magnonic-spheres to the weak-coupling regime. The material-limited
magnon dissipation rate in particular has been regarded as an unavoidable limitation in these systems. Here, we surpass this long-standing limitation by implementing an active microwave feedback loop to suppress the linewidth of cavity-
magnon polaritons and strongly suppress their effective decay rate below the
magnon-limited linewidth, thereby enhancing the polariton-
phonon cooperativity from C=1 to C=150. As a key milestone, we achieve normal-mode splitting between a cavity-
magnon polariton and a mechanical mode, providing direct evidence of three-mode hybridization among
photons,
magnons, and
phonons. Our results establish feedback as a general route to accessing strong-coupling regimes in systems previously thought to be limited by material properties and hence open new opportunities for coherent control in hybrid
quantum systems.
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All authors M. Ebrahimi, Y. Huang, V.A.S.V. Bittencourt, A. Rashedi, A. Metelmann, J.P. Davis
Mesoscale and Nanoscale Physics
Dissipative Nonlinear Phononics: Nonequilibrium Quasiperiodic Order in Light-Driven Spin-Phonon System
Brayan I. Eraso-Solarte and Yafei Ren
Nonlinear phononics has emerged as a powerful paradigm for the nonthermal control of
quantum materials by engineering a conservative potential energy landscape. Here, we show that dissipation can serve as an additional control knob for nonequilibrium states in nonlinear phononics. We reveal a nontrivial role of dissipation by investigating a
spin-
phonon coupled system driven by circularly polarized light. By tuning the
spin relaxation time $\tau_s$, the steady state undergoes a transition from a trivial limit cycle to a temporally ordered state, which spontaneously breaks the discrete time-translation
symmetry imposed by the drive. In this state, both the
spin and
phonon angular momentum exhibit persistent oscillations at an emergent frequency $\Omega_s$, which is generally incommensurate with the driving frequency. This state is stabilized by a dissipation-induced phase lag between
spin and
phonon angular momentum that generates a feedback loop sustaining the oscillation. The dissipation-controlled transition can be described within a Landau-type framework using a pseudo-potential, where the order parameter has a $U(1)$ phase
symmetry, and its amplitude is proportional to the oscillation amplitude of the
phonon angular momentum.
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Mesoscale and Nanoscale Physics
Magnetic-field-induced superconductivity in hexalayer rhombohedral graphene
Jinghao Deng, Jiabin Xie, Hongyuan Li et al. (+5 more)
In conventional
superconductors, superconductivity is generally suppressed by external
magnetic fields due to
spin-singlet pairing. Here, we report signatures of in-plane-
magnetic-field-induced superconductivity in hexalayer rhombohedral
graphene and reveal electric-field control of its depairing behavior. With the application of a small in-plane
magnetic field $B_{\parallel}$, a superconducting state emerges within a narrow band along a phase boundary. Its properties evolve continuously with increasing $B_{\parallel}$: the superconducting region progressively shifts toward higher electric field as the $B_{\parallel}$ increases and the transition temperature rises with increasing $B_{\parallel}$. Remarkably, the superconducting state remains robust under $B_{\parallel}$ up to 14 T, far exceeding the conventional Pauli limit.
Quantum oscillation measurements further reveal that the superconductivity emerges from nematic
Fermi surface reconstruction. These results suggest a
spin-polarized superconducting states with unconventional origins.
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All authors Jinghao Deng, Jiabin Xie, Hongyuan Li, Takashi Taniguchi, Kenji Watanabe, Jie Shan, Kin Fai Mak, Xiaomeng Liu
Materials Science
Efficient prediction of highly anisotropic excitonic properties in the layered antiferromagnet CrSBr via time-dependent density functional theory
Ashwin Ramasubramaniam, Daniel Hernangómez-Pérez, Javier Junquera et al. (+1 more)
CrSBr, a layered anisotropic van der Waals antiferromagnet, has recently emerged as a versatile platform where strong coupling between optical excitations and
magnetic order enables magneto-optical control in low dimensions. While experiments have progressed rapidly, predictive and reliable ab initio descriptions remain limited to self-consistent, many-body perturbation theory that is computationally expensive and technically challenging. Here we present an alternative approach that accurately predicts the electronic and optical properties of CrSBr at substantially lower computational cost, while retaining quantitative accuracy in the coupling between
excitons and
magnetic order. Using a tuned hybrid density functional with on-site corrections, we reproduce fundamental and optical gaps and quantitatively capture the interaction between excitonic transitions and
magnetic order. We then employ this functional to investigate excitonic shifts induced by
spin canting, that would result from applying an external
magnetic field. Our results establish an efficient framework for modeling excitonic and magneto-optical phenomena in layered
magnetic semiconductors.
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All authors Ashwin Ramasubramaniam, Daniel Hernangómez-Pérez, Javier Junquera, María Camarasa-Gómez
Strongly Correlated Electrons
Microscopic geometric theory for gapped excitations in fractional topological fluids
Yuzhu Wang and Bo Yang
We propose a
geometric description of all gapped excitations in fractional
quantum Hall phases that reveals several fundamental understandings with experimental consequences. These include a duality between the
Hilbert space of multiple gapped “graviton-like"
spin 2 excitations at $\nu=1/3$ Laughlin phase, and that of non-Abelian quasiholes of an irrational Haffnian conformal field theory. This leads us to construct microscopic wave functions for multiple higher-
spin gapped neutral modes in the Laughlin phase. Carrying
spin $s \ge 2$, they emerge from higher-order
geometric deformations of the topological ground state, and live within the Gaffnian conformal
Hilbert space asymptotically. We show that the full many-body
Hilbert space of an FQH phase can be generated from superpositions of such
geometric deformations, supporting a concrete
geometric interpretation of all gapped excitations. We analyse the scattering between these higher
spin modes and
conjecture that they can have a long lifetime, and propose methods for their experimental detection.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Distance learning from projective measurements as an information-geometric probe of many-body physics
Oleksii Malyshev, Simon M. Linsel, Fabian Grusdt et al. (+3 more)
The ability of modern
quantum simulators–both digital and analogue–to generate large ensembles of single-shot projective "snapshots" has opened a data-rich avenue for the study of
quantum many-body systems. Unsupervised machine learning analysis of such snapshots has gained traction, with numerous works reconstructing phase diagrams by learning and clustering low-dimensional representations of
quantum states. Here, we forgo such representation learning in favour of distance learning: we infer the pairwise distances between
quantum states–already sufficient for clustering–directly from snapshots. Specifically, we use a single neural discriminator to estimate Csiszar f-divergences–statistical distances between distributions–in an unsupervised manner. The resulting clusters reveal regimes with different dominant correlations, often coinciding with, but not limited to, conventionally defined phases of matter. Beyond phase-diagram exploration, we connect the infinitesimal limit of the inferred divergences to the Fisher information metric and analyse its finite-size scaling. This yields critical exponents of the discovered transitions and enables snapshot-based analysis of universality classes. We apply distance learning to a diverse set of systems characterised by conventional local order parameters (1D transverse-field and 2D classical Ising models), non-local topological order (extended toric code), and higher-order correlations (fermionic t-J model on a triangular
lattice). In all cases, we correctly recover boundaries between distinct correlation regimes and, where applicable, quantitatively match established critical behaviour. Finally, we show that distances to suitably chosen reference snapshot distributions help identify the dominant correlations within the discovered clusters, positioning distance learning as a versatile information-
geometric probe of
quantum many-body physics.
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All authors Oleksii Malyshev, Simon M. Linsel, Fabian Grusdt, Annabelle Bohrdt, Eugene Demler, Ivan Morera
Statistical Mechanics
Does Partial Consumption Help Foraging?
Md Aquib Molla and Sanchari Goswami
In this work, we consider partial consumption of food by a forager in presence of a threshold energy level. The forager considered here can survive for $S$ steps without food, namely the survival time. The threshold limits the consumption of food in such a way that, the forager will only consume food, whenever its energy is below the threshold $k$. Due to partial consumption of food, a site containing food may not always be fully depleted, which in turn helps in increasing the lifetime of the forager. It has been observed that, in our case, the lifetime always increases with $k/S$, although there is a transition threshold $k^*$ below which the increase of lifetime is rapid and above is slow. The transition threshold $k^* \sim \sqrt{S}$. The lifetime $\tau$ shows a power law behavior as $\tau \sim S^{\beta}$. For $k/S=0$, the value of $\beta$ is $1.331$, it then jumps above $2$ and decreases gradually to $1.833$ with increasing $k/S$. Other important quantities like number of revisits to a site, food statistics etc. have been studied and some interesting scaling behaviors are observed. Although, survival for each time unit requires, on an average, the consumption of one unit of food, the food consumption is not the only factor to control the lifetime of the forager. It has been observed that, the strategy in terms of threshold energy and partial consumption affects the lifetime in a positive way. The collection of sites either fully or partially depleted of food after the death of the forager shows a crossover behavior for $k/S \sim 0.5$.
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Statistical Mechanics · Cross-listed from quant-ph
Hadamard regularization of open quantum systems coupled to unstructured environments in the Schwinger-Keldysh formalism
Jakob Dolgner
The theory of open
quantum systems addresses how coupling to external degrees of freedom modifies observables and
quantum coherence, a situation central to fundamental condensed-matter research and emerging
quantum technologies. Schwinger-Keldysh field theory is a natural framework for both open- and nonequilibrium
quantum systems in terms of functional integrals. However, its numerical solution is limited by a cubic scaling with the number of time steps. This is particularly prohibitive for scenarios with widely separated time scales, as is often the case for system and environmental scales. We consider a damped
quantum harmonic oscillator as a toy model to study a separation-of-scales ansatz based on Hadamard regularization. A time-stepping
algorithm for the Kadanoff-Baym equations on the slow system time-scale is presented that captures both low-temperature non-Markovianity and renormalization effects arising from the much faster environment scale.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Characterization of Radiation-Induced Errors in Superconducting Qubits Protected with Various Gap-Engineering Strategies
H. Douglas Pinckney, Thomas McJunkin, Alan W. Hunt et al. (+26 more)
Impacts from high-energy particles cause correlated errors in superconducting
qubits by increasing the quasiparticle density in the vicinity of the Josephson junctions (JJs). Such errors are particularly harmful as they cannot be easily remedied via conventional error correcting codes. Recent experiments reduced correlated errors by making the difference in superconducting gap energy across the JJ larger than the
qubit transition energy. In this work, we assess gap engineering near the JJ ($\delta\Delta_{\mathrm{JJ}}$) and the capacitor/ground-plane ($\delta\Delta_{\mathrm{M1}}$) by exposing arrays of transmon
qubits to two sources of radiation. For $\alpha$-particles from an $^{241}$Am source, we observe $T_1$ errors correlated in space and time, supporting a hypothesis that hadronic
cosmic rays are a major contributor to the $10^{-10}$ error floor observed in Ref. 1. For electrons from a pulsed linear accelerator, we observe temporally correlated $T_1$ and $T_2$ errors, this measurement is insensitive to spatial correlations. We observe that the severity of correlated $T_1$ errors is reduced for
qubit arrays with a greater degree of gap engineering at the JJ. For both $T_1$ and $T_2$ errors, the recovery time is hastened by an increased $\delta\Delta_{\mathrm{M1}}$, which we attribute to the trapping of quasiparticles into the capacitor/ground-plane. We construct a model of quasiparticle dynamics that qualitatively agrees with our observations. This work reinforces the multifaceted influence of radiation on superconducting
qubits and provides strategies for improving radiation resilience.
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All authors H. Douglas Pinckney, Thomas McJunkin, Alan W. Hunt, Patrick M. Harrington, Hannah P. Binney, Max Hays, Yenuel Jones-Alberty, Kate Azar, Felipe Contipelli, Renée DePencier Piñero, Jeffrey M. Gertler, Michael Gingras, Aranya Goswami, Cyrus F. Hirjibehedin, Mingyu Li, Mathis Moes, Bethany M. Niedzielski, Mallika T. Randeria, Ryan Sitler, Matthew K. Spear, Hannah Stickler, Jiatong Yang, Wouter Van De Pontseele, Mollie E. Schwartz, Jeffrey A. Grover, Kevin Schultz, Kyle Serniak, Joseph A. Formaggio, William D. Oliver
Statistical Mechanics
Speed fluctuations of a stochastic Huxley-Zel'dovich front
Evgeniy Khain, Baruch Meerson and Pavel V. Sasorov
The empirical speed of travelling reaction-
diffusion fronts fluctuates due to the intrinsic shot noise of the reactions and
diffusion. Here we study the long-time front speed fluctuations of a
stochastic Huxley-Zel'dovich front. It involves a population of particles $A$ which perform a fast continuous-time random walk on a one-dimensional
lattice and undergo reversible on-site reactions $2A \rightleftarrows 3A$. This front describes an invasion of $A$-particles into an initially empty region of space which, in a deterministic description, is marginally stable but nonlinearly unstable with a zero instability threshold. Typical fluctuations of this front can be described as front
diffusion in a reference frame moving with the average front speed. According to the existing perturbation theory, the shot-noise-induced systematic shift of the average front speed, $\delta c$, and the front
diffusion coefficient, $D_f$, are both expected to scale with $N$ as $1/N$, where $N \gg 1$ is the typical number of particles in the transition region. Furthermore, $D_f$ can be determined perturbatively in the small parameter $1/\sqrt{N}$. Our Monte Carlo simulations support these asymptotic results, but also reveal a long-lived anomalous behavior of the first few particles before they reach the expected
diffusion asymptotic. We also study large deviations of the empirical speed of the front at long times. These are dominated by optimal histories of the system in the form of a propagating front which travels with a speed different from the average speed, or even travel in the wrong direction.
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Mesoscale and Nanoscale Physics
Ultrafast photo-thermoelectric currents in graphene junctions in the mid-infrared
Nina Pettinger, Michel Panhans, Johannes Schmuck et al. (+8 more)
Graphene is widely recognized for its ultrafast and broadband photocurrent response, but whether the broadband ultrafast characteristics are preserved at mid-infrared wavelengths with
photon energies below the optical
phonon energy remains an open question. Here, we investigate the carrier dynamics in
graphene junctions under mid-infrared excitation using an ultrafast pump-probe photocurrent spectroscopy. We utilize dual split gate devices to demonstrate that the photo-thermoelectric effect can dominate the photoresponse of
graphene also for a mid-infrared femtosecond excitation. We observe that
graphene retains its broadband photocurrent response in this spectral region, but the photocurrent relaxation time increases from ca. 2 ps below 8-9 micrometer up to 3 ps at longer mid-infrared wavelengths. The absence of a pronounced
phonon bottleneck in the decay dynamics at room temperature suggests an efficient interplay of electron-electron and electron-
phonon scattering even for
photon energies below the optical
phonon energy in
graphene. The observed wavelength dependence of the photocurrent relaxation times is consistent with energy-dependent theoretical relaxation times as derived from a microscopic transport theory of
graphene that includes electron-
phonon coupling within a Holstein-Peierls
Hamiltonian.
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All authors Nina Pettinger, Michel Panhans, Johannes Schmuck, Sebastian Loy, Xiaoyi Zhou, Chengye Dong, Joshua A. Robinson, Sergey Zherebtsov, Christoph Kastl, Frank Ortmann, Alexander W. Holleitner
Materials Science
Diffusion-based Generative Machine Learning Model for Predicting Crack Propagation in Aluminum Nitride at the Atomic Scale
Jiali Lu and Shengfeng Yang
Predicting atomic-scale crack propagation in aluminum nitride (AlN) is critical for
semiconductor reliability but remains prohibitively expensive via molecular dynamics (MD). We develop a
diffusion-based generative machine learning model to predict atomic-scale crack propagation in AlN, a critical
semiconductor material, by conditioning solely on initial microstructure
embeddings. Trained on MD simulations of single-crack systems, the model achieves a significant speedup while accurately
forecasting dynamic fracture processes, including stress-driven crack initiation, crack branching, and atomic-scale bridging ligaments. Crucially, it demonstrates inherent physical fidelity by reproducing material-intrinsic mechanisms while disregarding periodic boundary artifacts, and generalizes to unseen multi-crack configurations. Validation against MD ground truth confirms the capability of the model to capture complex fracture physics without auxiliary stress or energy data, enabling rapid exploration of crack-mediated failure for
semiconductor reliability optimization.
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Materials Science · Cross-listed from stat.ML
Filtered Spectral Projection for Quantum Principal Component Analysis
Sk Mujaffar Hossain and Satadeep Bhattacharjee
Quantum principal component analysis (qPCA) is commonly formulated as the extraction of
eigenvalues and eigenvectors of a covariance-encoded density operator. Yet in many qPCA settings the practical goal is simpler: projection onto the dominant spectral subspace. Here we introduce a projection-first framework, the Filtered Spectral Projection
Algorithm (FSPA), which bypasses explicit
eigenvalue estimation while preserving the relevant spectral structure. FSPA amplifies any nonzero warm-start overlap with the leading subspace and remains robust in small-gap and near-degenerate regimes, without artificial
symmetry breaking in the absence of bias. We show that FSPA achieves an oracle complexity $\mathcal{O}((\log(1/\epsilon)+\log(1/|a_1|^2))/\log(\lambda_1/\lambda_2))$,which is tight by a matching lower bound, establishing it as anoptimal projection primitive. We derive a convergence rate for degenerate spectra, give a
circuit resource analysis with $n+\mathcal{O}(1)$
qubit overhead independent of system dimension, and extend the method to threshold spectral projection, Threshold-FSPA, which converges in $\mathcal{O}(\log(1/\epsilon))$ calls when the threshold lies between
eigenvalues. In the density
matrix exponentiation access model, FSPA gives an exponential copy-complexity advantage over classical methods. For classical
datasets, we show that for amplitude-encoded centered data the ensemble density
matrix $\rho=\sum_i p_i|\psi_i\rangle\langle\psi_i|$ equals the covariance
matrix. Numerical tests on chemistry density
matrices, noisy
circuit outputs, Breast Cancer Wisconsin, handwritten Digits, and 1–4-
qubit scalability confirm the theory. A minimal Qiskit implementation validates magnitude invariance, signal amplification, and no spurious
symmetry breaking. These results establish FSPA as an optimal and deployable
quantum spectral projection primitive.
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Materials Science · Cross-listed from physics.ins-det
Development of a high-field pulsed magnet and optical fiber coupled cryostat system for magneto-photoluminescence measurements
Deepesh Kalauni, Kingshuk Mukhuti, Tao Peng et al. (+1 more)
This paper presents the development of a high field pulsed magnet system combined with an optical fiber-coupled low temperature cryostat for magneto-photoluminescence measurements. A novel aspect of our system is the use of electrolyte capacitors in a 75 kJ capacitor bank to drive the pulsed magnet, enabling the generation of high
magnetic fields at a relatively low charging voltage (400 V). The zylon reinforced wire wound magnet coil achieves a maximum field strength of 35 tesla with a
magnetic field rise time of 10 ms. The integrated cryostat was developed to meet the specific requirements of magneto-photoluminescence experiments using a 4 K helium closed-cycle cryocooler to provide a stable low-temperature environment down to 5 K.
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All authors Deepesh Kalauni, Kingshuk Mukhuti, Tao Peng, Bhavtosh Bansal
Mesoscale and Nanoscale Physics
Semiclassical magnetotransport in Weyl semimetals with skyrmion-induced emergent magnetic fields
Azaz Ahmad and Takami Tohyama
We investigate magnetotransport in a time-reversal
symmetry-broken, untilted Weyl semimetal in the simultaneous presence of momentum-space Berry
curvature and skyrmion-induced emergent
magnetic fields $\mathbf{B}_{\mathrm{emer}}$. Using a semiclassical Boltzmann approach incorporating Berry-
curvature corrections and intervalley scattering, we analyze the longitudinal magnetoconductivity and planar
Hall conductivity in this mixed-
topology regime. In the absence of $\mathbf{B}_{\mathrm{emer}}$, increasing intervalley scattering drives a strong sign reversal of the longitudinal magnetoconductivity. A finite $\mathbf{B}_{\mathrm{emer}}$ introduces an additional shift of the
parabolic magnetic-field dependence, leading to a weak sign-reversal regime without altering the
curvature. The coexistence of these effects naturally produces a strong-and-weak sign-reversal regime, demonstrating that intervalley scattering and real-space
topology control distinct
geometric features of the response. The emergent field further induces asymmetry in the angular dependence of both longitudinal and planar
Hall conductivities. We show that a finite planar
Hall response can arise solely from $\mathbf{B}_{\mathrm{emer}}$ when its direction is varied, providing a transport signature of real-space
topology. Our results establish that the skyrmion-induced emergent field acts as an independent topological tuning parameter, revealing measurable consequences of the interplay between real- and momentum-space Berry
curvature in Weyl systems.
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Strongly Correlated Electrons
Two-channel physics in a lightly doped antiferromagnetic Mott insulator revealed by two-hole spectroscopy
Pit Bermes, Sebastian Paeckel, Annabelle Bohrdt et al. (+2 more)
Understanding pairing in the strong-coupling regime of doped Mott
insulators remains an open problem in the context of cuprate
superconductors. We perform ultra-high resolution numerical simulations of spectral functions in the highly underdoped $t-J$ model and discover two coupled branches of hole pairs emerging at low energies in the largely unexplored two-particle spectrum. As
spin anisotropy is tuned from the Ising limit to the $SU(2)$-symmetric Heisenberg regime, the lowest $d$-wave pair evolves from a single bipolaronic branch into two hybridized branches separated by an avoided crossing. We explain this behaviour using an effective two-channel model involving a tightly bound bipolaronic state and a second channel associated with two
magnetic polarons. The model reproduces the qualitative low-energy spectra and implies near-resonant $d$-wave interactions in the $SU(2)$-symmetric $t-J$ model, consistent with proximity to an emergent Feshbach-type resonance. To probe these predictions experimentally, we propose a Raman spectroscopy scheme for the attractive Hubbard model that can be directly implemented using ultracold atoms in optical
lattices. Our work establishes two-particle spectroscopy, beyond single-particle Green's functions, as a powerful tool for revealing the microscopic origins of unconventional superconductivity.
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All authors Pit Bermes, Sebastian Paeckel, Annabelle Bohrdt, Lukas Homeier, Fabian Grusdt
Materials Science
Electromechanical Hysteresis in Phase Change Material Sb2S3
Jack Kaman, Evan Musterman, Kyle P. Kelley et al. (+3 more)
Antimony sulfide is an emerging phase change material for optical and electrical
memory and computation elements. It has additionally been reported as a ferroelectric, with recent evidence from hysteresis in piezoresponse force microscopy. Here, we complete a rigorous set of piezoresponse force microscopy experiments on a congruently crystallized Sb2S3 glass-ceramic, where piezoelectric coupling should be forbidden in glassy Sb2S3. We replicate previous results and reveal that the behavior is absent in glassy Sb2S3 but show that the response originates primarily from non-piezoelectric contributions to the signal caused by an applied voltage. This hysteretic behavior in piezoresponse force microscopy is quite similar to some electrochemically active non-ferroelectric
oxides, but uniquely, it appears here with a very clear spatial contrast that is decoupled from surface topography. This shows that the electromechanical signal reflects bulk-like properties and reveals differences in electrical behavior of crystalline and amorphous phases of Sb2S3.
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All authors Jack Kaman, Evan Musterman, Kyle P. Kelley, Neus Domingo-Marimon, Volkmar Dierolf, Himanshu Jain
Mesoscale and Nanoscale Physics
First-principles predictions of band alignment in strained Si/Si1-xGex and Ge/Si1-xGex heterostructures
Nathaniel M. Vegh, Pericles Philippopoulos, Raphaël J. Prentki et al. (+4 more)
Accurate band offsets are essential for predictive continuum modeling of nanostructures such as
quantum wells and
quantum dots formed in strained Si/Si1-xGex and Ge/Si1-xGex
heterostructures. Experimental offset data for these systems remain sparse away from endpoint compositions, making composition-dependent design difficult. We use atomistic first-principles density functional theory to compute valence- and conduction-band offsets across the full range 0 <= x <= 1. Random alloying is treated with special quasirandom structures, interface lineup terms are extracted from macroscopically averaged local Kohn-Sham potentials in thick periodic superlattices, valence-band
spin-orbit coupling is included through species-resolved Mulliken weights, and conduction-band edges are refined using the screened hybrid Heyd-Scuseria-Ernzerhof functional. The resulting offsets show pronounced composition nonlinearity beyond the linear models explored in previous works, agree with experimental
benchmarks, and reproduce the high-Ge slope change in the relaxed-
alloy band gap. Analytic fitting expressions are provided for direct use in simulations, facilitating practical design of modern
quantum technology devices.
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All authors Nathaniel M. Vegh, Pericles Philippopoulos, Raphaël J. Prentki, Wanting Zhang, Yu Zhu, Félix Beaudoin, Hong Guo
Disordered Systems and Neural Networks · Cross-listed from math-ph
Robust symmetry breaking in gapless quantum magnets
Chao Yin and Andrew Lucas
We prove the existence of spontaneous
symmetry breaking in suitably low-energy eigenstates of certain gapless and frustrated many-body
quantum systems, namely symmetric
quantum perturbations to classical models which exhibit spontaneous
symmetry breaking of a finite group at some positive temperature. Additionally, the classical model need not be local in space, as long as it satisfies a
quantum analogue of the Peierls condition. As an example of our technique, we establish robust ferromagnetism in random-bond Ising models in $d= 2$ dimensions with sufficiently biased random couplings, with weak transverse field. Our mathematical technique is based on establishing
quantum bottlenecks, similar to a "many-body WKB" method for evaluating tunneling rates. Using these same methods, we provide new proofs of metastability and the slow decay of the false
vacuum, applicable to gapless metastable states. Our work represents a first step towards a rigorous classification of stable gapless
quantum phases.
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Materials Science
A Spatial Localizer for Electrons in Insulators
Haylen Gerhard, Yifan Wang, Alexander Cerjan et al. (+1 more)
The location of electrons governs phenomena ranging from chemical bonding and electric polarization to the topological classification of band
insulators and the emergence of correlated states in
quantum matter. While a prescription exists for finding local state representations of electrons in one-dimensional
insulators, no comparably general theory exists in higher dimensions. Here, we introduce a general framework for finding the location of electrons in
insulators in two and three dimensions based on the spectral properties of
quantum-mechanical operators that we term Spatial Localizers. This framework naturally extends the notion of Wannier centers to
insulators with boundaries, defects, and disorder, which we use to establish a position-space formulation of the bulk-defect correspondence for electronic charge. This framework also yields maximally localized electronic states. As two representative examples, we show that these states reduce to maximally localized Wannier functions in atomic
insulators, whereas in Chern
insulators they form coherent states that mirror the coherent-state structure of Landau levels in the
quantum Hall effect.
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All authors Haylen Gerhard, Yifan Wang, Alexander Cerjan, Wladimir A. Benalcazar
Materials Science
Microscopic flexoelectricity in the canonical PMN relaxor
J. Hlinka
Previously reported
neutron scattering investigations of the canonical relaxor ferroelectric perovskite
oxide with a chemical formula Pb(Mg(1/3)Nb(2/3))O3 (PMN) are revisited in order to appreciate the role of the intrinsic bulk flexoelectricity. Despite the outstanding electromechanical properties of lead-based relaxors, the magnitude of the flexoelectric coupling coefficient derived here directly from the PMN
neutron diffuse scattering data, does not exceed the range of values typical for conventional perovskite ferroelectrics. We explain how these findings are related in the framework of the Ginzburg-Landau-Devonshire and the ferroelectric soft mode theory. We propose that the relaxor properties of PMN might be related to the suppression of the transverse correlation length of the flexoelectrically hybridized translational-polarization fluctuations due to its closeness to the Lifshitz-point regime.
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Materials Science · Cross-listed from physics.comp-ph
From Experiments to Expertise: Scientific Knowledge Consolidation for AI-Driven Computational Physics
Haonan Huang
While large
language models (LLMs) have transformed AI
agents into proficient executors of computational materials science, performing a hundred simulations does not make a researcher. What distinguishes research from routine execution is the progressive accumulation of knowledge - learning which approaches fail, recognizing patterns across systems, and applying understanding to new problems. However, the prevailing paradigm in AI-driven computational science treats each execution in isolation, largely discarding hard-won insights between runs. Here we present QMatSuite, an open-source platform closing this gap.
Agents record findings with full provenance, retrieve knowledge before new calculations, and in dedicated reflection sessions correct erroneous findings and synthesize observations into cross-compound patterns. In
benchmarks on a six-step
quantum-mechanical simulation workflow, accumulated knowledge reduces
reasoning overhead by 67% and improves accuracy from 47% to 3% deviation from literature - and when transferred to an unfamiliar material, achieves 1% deviation with zero pipeline failures.
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Materials Science · Cross-listed from cs.CE
Lattice Discrete Particle Model (LDPM): Comparison of Various Time Integration Solvers and Implementations
Erol Lale, Jan Eliáš, Ke Yu et al. (+17 more)
This article presents a comparison of various implementations of the
Lattice Discrete Particle Model (LDPM) for the numerical simulation of concrete and other heterogeneous quasibrittle materials. The comparison involves the use of transient implicit and explicit solvers and steady-state (static) solvers and implementations for Central Processing Unit (CPU) as well as Graphics Processing Unit (GPU). The various implementations are compared on the basis of a set of
benchmarks tests describing behaviors of increasing computational complexity. They include elastic vibrations, confined strain-hardening compressive response, tensile fracture, and unconfined strain-softening compressive response. Metrics of interest extracted from the simulations include macroscopic stress versus strain responses, computational times, number of iterations, and energy balance error. Pairwise comparison of final crack patterns is provided through the correlation coefficient and normalized root mean square error of the crack opening vectors. Moreover, for the most numerically challenging case of unconfined compression with sliding boundary conditions, the stability of the strain-softening response is tested by perturbing the solutions as well as changing the convergence criteria and time step size. Attached to this paper is the complete input data of the
benchmark tests; this will allow researchers to run the examples and compare them with their own implementations. In addition, most of the reported implementations are publicly available in open source packages.
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All authors Erol Lale, Jan Eliáš, Ke Yu, Matthew Troemner, Monika Středulová, Julien Khoury, Tianju Xue, Ioannis Koutromanos, Alessandro Fascetti, Bahar Ayhan, Baixi Chen, Giovanni Di Luzio, Yuhui Lyu, Madura Pathirage, Gilles Pijaudier-Cabot, Lei Shen, Alessandro Tasora, Lifu Yang, Jiawei Zhong, Gianluca Cusatis
Mesoscale and Nanoscale Physics
Unified Theory of Spin and Orbital Inverse Faraday Effects in Rashba Metals
Jaglul Hasan, Maxim Dzero and Chandan Setty
The inverse Faraday effect (IFE) offers a promising route toward optical control of
magnetic moments in
quantum materials. Yet experiments on
spin-orbit-coupled metals indicate that no single microscopic mechanism suffices, implicating orbital currents alongside
spin polarization. We derive both responses in a disordered Rashba metal using
quantum kinetics and diagrammatics with
impurity-renormalized optical vertices, providing the first unified diagrammatic derivation of
spin and orbital IFE. Treating
impurity scattering consistently, our number-conserving kinetic formulation restores full phase-space derivatives and the optical
magnetic field neglected in earlier treatments. We connect nonlinear orbital magnetization to absorptive linear optical conductivity, revealing that the
magnetic Lorentz force supplies half the orbital response. Our unified treatment resolves both channels across the Rashba resonance:
spin IFE changes sign as frequency increases, while the orbital IFE dominates, keeping the direction of the total magnetization unchanged.
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