Peer Revenue Equity in science

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Condensed Matter

cond-mat Watch Condensed Matter

Monday 1 June

Disordered Systems and Neural Networks

Structural glasses model using disorder fields: the boson peak from local ground states

M. M. Balbino, I. P. de Freitas, A. M. S. Macedo et al. (+2 more)

We show the emergence of a contribution characteristic of the boson peak in the spectral density of structural glasses. To model the vitreous state, we consider static density-fluctuation fields coupled to a multiplicative quenched disorder. Performing an ensemble average over all disorder realizations, a functional series representation of the average free energy is obtained. In this series representation of the average free energy for the glassy state of matter, we identify in the function space effective actions. These effective actions present a large number of metastable states and ground states. Random first-order transition, widely discussed in the literature as a description of the transition from the supercooled liquid to the glassy state of matter, emerges naturally in our formalism. We establish the connection between the use of hyperbolic differential equations with random coefficients and the presence of many ground states in the average free energy. This connection allows us to study emergent excitations in such amorphous materials.
Read the full abstract

All authors M. M. Balbino, I. P. de Freitas, A. M. S. Macedo, G. Krein, N. F. Svaiter

Disordered Systems and Neural Networks

Scaling Laws for Neural-Network Quantum States

Riccardo Rende, Alessandro Sinibaldi, Luciano Loris Viteritti et al. (+3 more)

Scaling laws, the power-law relations between loss, architecture size, and compute observed in modern neural networks, offer a quantitative way to characterize the complexity of a learning problem, with the exponent governing the decay of the loss reflecting how rapidly additional resources translate into improved accuracy, and thus how hard the target is to learn. Whether an analogous framework can characterize the complexity of physical problems remains open. We address this question for Neural-Network Quantum States, a leading variational approach for strongly correlated quantum many-body systems. Using transformer wave functions to approximate ground states of the $J_1$-$J_2$ Heisenberg model on triangular and square lattices with up to $20\times 20$ sites, we find that the $V$-score, a measure of accuracy of a variational state, decays as a power law in training compute. Under an appropriate rescaling of compute, results for different system sizes collapse onto a single curve, analogous to scaling collapse in critical phenomena. The resulting power law is, to a good approximation, independent of the number of sites, showing that the transformer Ansatz is size-consistent for the systems considered. The exponent decreases systematically with frustration, identifying it as a quantitative measure of representational difficulty of the ground state and establishing scaling laws as a general framework for benchmarking variational ansätze.
Read the full abstract

All authors Riccardo Rende, Alessandro Sinibaldi, Luciano Loris Viteritti, Roeland Wiersema, Antoine Georges, Giuseppe Carleo

Strongly Correlated Electrons

Skyrmion and meron phases induced by spin-phonon coupling

E. Iroulart, F. A. Gómez Albarracín and H. Diego Rosales

In chiral magnets, magnetic skyrmions are typically stabilized by the competition between exchange and Dzyaloshinskii-Moriya (DM) interactions under an external magnetic field, while the role of lattice degrees of freedom has received comparatively less attention. Here we study how spin-phonon (SP) coupling modifies magnetic interactions and the resulting spin textures in a two-dimensional skyrmion model in the square lattice. Using Monte Carlo simulations, we compare two simplified models describing the SP coupling: the Einstein site-phonon (ESP) and bond-phonon (BP) models. Integrating the lattice degrees of freedom, we obtain effective Hamiltonians for each SP model, which involve three-spin interactions and quadratic terms. In both cases, skyrmion crystals are stabilized in field regimes that are topologically trivial in the uncoupled model. Moreover, in certain regimes, the conventional triple-$\qv$ hexagonal skyrmion lattice is distorted into a double-$\qv$ square skyrmion lattice. Additionally, we find that, in the ESP model, strong phonon coupling affecting the exchange interactions drives the system from typical low-field helical phases to meron-antimeron crystals with no net chirality. Overall, our results show that lattice effects provide a simple mechanism to tune a wide variety of topological magnetic phases, ranging from typical skyrmion crystals to distorted arrangements of skyrmions, elongated bimerons and meron-antimeron phases.
Read the full abstract

Superconductivity

Early Experiments on Macroscopic Quantum Tunneling

Willem den Boer

Before conclusive evidence of Macroscopic Quantum Tunneling, MQT, was published by Clarke, Devoret and Martinis in 1985, several other groups reported experimental results interpreted as MQT. The first, in chronological order, was in 1980 based on studies done at Leiden University in 1979. This paper looks back at these experiments on low capacitance Niobium point contacts in an rf SQUID, radio-frequency Superconducting Quantum Interference Device, configuration at temperatures between 1 and 4.2 K. The research was inspired by the theoretical predictions by Ivanchenko and Zilberman in 1969 on MQT in current-biased Josephson junctions and by Leggett in 1978 on MQT in closed loops with a superconducting weak link.
Read the full abstract

Strongly Correlated Electrons

Spin-$s$ model with competing interactions on diamond-decorated lattices

D. V. Dmitriev, V. Ya. Krivnov and O. A. Vasilyev

We investigate the ground state properties, magnetization, and low-temperature thermodynamics of the ferromagnetic-antiferromagnetic spin-$s$ model on diamond-decorated lattices with ideal diamond units, incorporating bilinear Heisenberg and higher-order exchange interactions between diagonal spins-$\sigma$. Local conservation of the composite spin on each diamond diagonal enables exact analysis. For the pure Heisenberg case, the system undergoes a series of $2\sigma$ transitions between monomer-dimer (MD), ferrimagnetic (Ferri) and ferromagnetic (F) phases with different optimal composite spin values as the coupling ratio varies. In the presence of higher-order interactions, a multicritical point exists where the states with all possible values of composite spin are degenerate, leading to maximal ground state degeneracy. The case $s=\sigma=1$ with bilinear and biquadratic interactions is studied in detail. Its phase diagram comprises three phases - F, Ferri and MD, which meet at a triple point. On the phase boundaries, the ground state becomes macroscopically degenerate. For the diamond chain, we calculate the ground state degeneracy exactly; for higher dimensions, the problem maps onto a bond percolation framework, solved numerically. The residual entropy per spin reaches up to $60\%$ of the maximal value, peaking at the triple point. Low-temperature magnetization curves in external magnetic fields exhibit plateaus and jumps. The excitation spectrum is gapped in the MD phase, gapless in the F phase, and resembles that of the Lieb-Mattis ferrimagnet in the Ferri phase. The high residual entropy suggests potential applications in ultra-low-temperature cooling and quantum thermal machines.
Read the full abstract

Superconductivity · Cross-listed from quant-ph

Superconducting Qubits with Altermagnetic Josephson Junctions

Johanne Bratland Tjernshaugen, Morten Amundsen and Jacob Linder

Identifying a materials platform for creating qubits that are both tunable and resilient towards environmental noise is one of the main hurdles that need to be overcome to realize quantum computation that is practically useful. One pursued avenue to this end is to use superconducting qubits with intrinsic spin-dependent interactions, such as spin-orbit coupling or magnetism. However, the recently discovered class of materials known as altermagnets remains largely unexplored in this context. We here use microscopic calculations to determine how the properties of superconducting qubits are modified when altermagnetic Josephson junctions are included. The key qubit performance parameters, including splitting, anharmonicity, decoherence, and single/coupled-qubit gate operation times, display rich behavior depending on the characteristic properties of the altermagnetic material, such as the strength of the Néel field and the crystallographic orientation of the altermagnetic relative to the interfaces in the system. We focus in particular on the transmon design and show that the qubit is very well protected against decoherence and simultaneously shows superior anharmonicity both near 0-$\pi$ transition points and when it is in a $\phi$-state. We propose that by using strain, the altermagnetic qubit can be moved out of its protected regime to enable faster gate operation times, and then moved back to its protected state. We establish the physical mechanism underlying the behavior of all central qubit metrics, clarifying how real devices interpolate between an altermagnetic double-well regime exhibiting barrier-induced protection and a conventional transmon-like single-well regime. We also discuss how the altermagnetic properties influence flux qubits and fluxonium.
Read the full abstract

Materials Science

Optoelectronics and Magnetic properties calculation of RE$_2$MnNiO$_6$ (RE=La-Lu,Y) using Density Functional Theory

Debidutta Pradhan

RE$_2$MnNiO$_6$ (RE = La-Lu) family of ordered double-perovskite oxides hosts a corner-sharing network of alternating NiO$_6$ and MnO$_6$ octahedra whose electronic and magnetic ground states are systematically governed by the A-site ionic radius through the lanthanide contraction. The strong localisation of RE 4f electrons poses a fundamental challenge to density-functional treatments, yet the hybridisation between 4f and neighbouring 5d (RE) or 3d (Ni, Mn) states is central to the origin of exchange interactions and optoelectronic response across the series. We present a comprehensive first-principles study of the electronic structure, lattice dynamics, and optical properties of representative RE2NiMnO6 compounds within the DFT+U framework. To disentangle the role of Kondo-type 4f-d hybridisation, calculations are performed with the RE 4f electrons treated both as frozen core states and explicitly in the valence manifold, enabling a direct assessment of their contribution to the band structure, dielectric function, and phonon dispersion. Spin-polarised calculations reveal significant spin-channel asymmetry, with magnetic moments reaching up to 30 $\mu$B per formula unit for select members of the series. The results establish a unified picture of how 4f occupancy and octahedral distortion collectively determine the magnetic and optoelectronic potential of this double-perovskite family.
Read the full abstract

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Vector Magnetometry with Broadband Microwave Fields in Nitrogen-Vacancy Centers in Diamond

Tom R. Rieckmann, Arezoo Afshar, Aaron Z. Goldberg et al. (+3 more)

We present a novel method for full vector magnetometry using nitrogen-vacancy (NV) centers. In contrast to conventional optically detected magnetic resonance techniques, our method employs two distinct broadband microwave pulses and measures them after transmission through the NV sensor medium, thus capturing the line splitting of the ground state triplet due to the Zeeman effect. Two orthogonally polarized microwave pulses allow resolving all magnetic field components independently by reading out differently oriented NV centers. Simulated data is analyzed using deep neural networks, whose efficacy we expect to translate very well to experiments. Our method yields sensitivities between $5~\mathrm{pT}/\sqrt{\mathrm{Hz}}$ and $100~\mathrm{pT}/\sqrt{\mathrm{Hz}}$ across different magnetic field vector components, while achieving approximately $\mathrm{nT}$ accuracy at a signal-to-noise (SNR) ratio of $70~\mathrm{dB}$. By being capable of accurately measuring magnetic fields down to $25~\mathrm{\mu T}$, the need for a bias field beyond Earth's magnetic field is eliminated.
Read the full abstract

All authors Tom R. Rieckmann, Arezoo Afshar, Aaron Z. Goldberg, Lilian Childress, Stefan Scheel, Khabat Heshami

Statistical Mechanics · Cross-listed from quant-ph

Geometric Decoherence Time in Lindbladian Dynamics

Rishabh Jha, Stephan Haas and Abhinav Prem

The onset of decoherence in open many-body systems lacks a dynamical timescale grounded in the loss of bipartite entanglement. Here, we introduce the $geometric$ $decoherence$ $time$, defined as the earliest moment the monotone relation between logarithmic negativity and Rényi-$\tfrac{1}{2}$ entropy – exactly equal across any bipartition for pure states – breaks down under open-system evolution, signaling entropy growth without accompanying entanglement growth. We establish this criterion in both single-particle Gaussian dynamics and many-body Lindbladian evolution. We show that quantum mutual information provides a complementary long-time diagnostic: its asymptotic vanishing is equivalent to factorization of the steady state across the bipartition, a condition strictly stronger than separability, and whenever a product steady state is approached exponentially in trace norm, negativity and mutual information share the same decay rate. In the presence of a strong symmetry, this tracking can fail – residual classical correlations can survive after entanglement has vanished. In the Kitaev chain with balanced gain and loss, we derive a closed-form solution and show that the topological phase sustains longer coherence times than the trivial phase at identical dissipation, with a local minimum at the chiral-symmetric point. In the interacting XXZ chain, exact many-body evolution shows that local $Z$-dephasing preserves residual classical correlations, whereas gain and loss restore the mutual-information tracking of negativity. Our results establish the geometric decoherence time as a dynamical scale tracking the onset of decoherence.
Read the full abstract

Disordered Systems and Neural Networks

Coexistence of topologically nontrivial and trivial insulating states in topological Anderson Chern insulator

Bo Yin, Yan Zhang, Anqi Wang et al. (+3 more)

The interplay between disorder and topology has become a central theme in condensed matter physics. Disorder can not only destroy topological phases but also induce them, as exemplified by the topological Anderson insulator (TAI). Here we show that, in close analogy, disorder can drive the clean-limit, time-reversal-broken(T-broken) quantum spin Hall state of ferromagnetic(FM) monolayer MnBi4Te7 into a quantum anomalous Hall phase, which was called topological Anderson Chern insulator (TACI). Using density functional theory (DFT) and nonequilibrium Green's func tion (NEGF) calculations in the presence of disorder, we identify disorder induced phases-including T-broken TAI, TACI, Normal insulator, etc., then construct a comprehensive phase diagram. To discriminate multiple phases in the strong disorder regime, we further use the density of states computed within the self-consistent Born approximation (SCBA), which in particular distinguishes gapped and ungapped topological phases. We find that the two effective band inversions of Hamiltonian are suppressed at distinct critical disorder strengths; the survival of a single inversion over a finite disorder window stabilizes the TACI. Remarkably, at strong disorder, we further propose a zero Hall plateau insulating state characterized by an insulating bulk and edge channels subject to diffusive scattering that can coexist with the TACI. This behavior is distinct from a conventional band-gap Chern insulator and provides a clear experimental signature.
Read the full abstract

All authors Bo Yin, Yan Zhang, Anqi Wang, Jie Shen, Zhijun Wang, Quansheng Wu

Superconductivity

Anharmonic lattice dynamics and superconductivity in strained bulk and surface niobium

Mihir Ranjan Sahoo, Roman Lucrezi, Pedro Nunes Ferreira et al. (+5 more)

Using first-principles calculations, we investigate how homogeneous strain and crystallographic surface orientation modify the vibrational and superconducting properties of niobium. For bulk Nb, tensile strain strongly softens the phonon spectrum and enhances the electron–phonon coupling, increasing the superconducting transition temperature from 9.5 K at equilibrium to 14.5 K at $\sim\!6\%$ lattice expansion. For the low-index Nb(001), Nb(110), and Nb(111) surfaces, harmonic phonon calculations exhibit imaginary modes, showing that anharmonic lattice effects are essential. To treat these effects efficiently, we train Nb-specific machine-learning interatomic potentials on bulk and slab first-principles configurations and use them to accelerate stochastic self-consistent harmonic approximation calculations, thereby obtaining anharmonically renormalized phonon modes that are combined with density-functional perturbation theory electron–phonon matrix elements to construct the Eliashberg spectral function. Among the clean free-standing slabs considered here, Nb(001) exhibits the strongest electron–phonon coupling and the highest calculated transition temperature of 10.0 K, while Nb(110) and Nb(111) show progressively reduced pairing strength. Finally, by analyzing the Eliashberg spectral function and the functional derivative $\delta T_\text{c}/\delta\alpha^2F(\omega)$, we identify the phonon energy ranges most effective for superconducting pairing. Our results show that strain, surface termination, and anharmonic phonon renormalization provide complementary and interrelated microscopic routes for tuning superconductivity in Nb.
Read the full abstract

All authors Mihir Ranjan Sahoo, Roman Lucrezi, Pedro Nunes Ferreira, Chia-Nien Tsai, Matthew Julian, Rohit P. Prasankumar, Mahmoud I. Hussein, Christoph Heil

Strongly Correlated Electrons

Simulating Condensed Matter Physics on Quantum Hardware

Ruizhe Shen, Tianqi Chen, Tommy Tai et al. (+3 more)

Quantum hardware platforms are getting increasingly sophisticated in their ability to simulate condensed matter, including but not limited to strongly-correlated, topological, and non-equilibrium phenomena. This review surveys recent progress in quantum-hardware-based simulations of condensed matter, primarily emphasizing gate-based digital quantum computer simulation, with analog experiments discussed as complementary benchmarks. We first review major hardware platforms, including superconducting qubits, trapped-ions, ultracold atoms, Rydberg arrays, photonic systems, and moire quantum materials. We then introduce the basic ingredients of digital quantum simulation. Building on this foundation, we discuss representative applications to condensed-matter physics, spanning ground-state problems, strongly correlated matter, topological phases, non-equilibrium dynamics, open-system physics, and high-energy-physics-inspired simulations. Finally, we summarize key methodological tools used in state-of-the-art quantum-simulation workflows. We emphasize that present noisy quantum simulations serve not only as near-term demonstrations, but also as prototypes for the encodings, diagnostic protocols and error-control strategies required for future fault-tolerant quantum simulation.
Read the full abstract

All authors Ruizhe Shen, Tianqi Chen, Tommy Tai, Jin Ming Koh, Pouyan Ghaemi, Ching Hua Lee

Strongly Correlated Electrons

Two-orbital $e_g$ model with bond-dependent spin-orbit coupling: A playground for emergent band topology, Kitaev magnetism, and magnetoelectricity

YuZheng Xie, Manoj Gupta, Arun Paramekanti et al. (+1 more)

Inspired by the electronic structure of compounds like nickel dihalides Ni$X_2$ ($X$=Cl, Br, I), we propose a low-energy two-orbital $e_g$ model featuring bond-dependent spin-orbit terms, driven by atomic spin-orbit coupling on the ligand $X$. We demonstrate that this model hosts a rich array of phenomena. In the non-interacting band limit, spin-orbit-derived spin-dependent and spin-flip hopping terms produce topological bands with spin-Chern numbers $C_s=\pm 2, \pm 4$, and higher order topological states with fractional corner charges, respectively. In the half-filled Mott insulator limit, we recover a spin-$1$ Hamiltonian with bond-dependent Kitaev exchange interactions. We explore the magnetoelectric effect in this two-orbital model using symmetry-based perspective and microscopic calculations, going beyond the generalized Katsura-Nagaosa-Balatsky theory for the single-orbital case. Our work may be relevant to study of doping, strain, or pressure on Ni$X_2$ and related materials.
Read the full abstract

All authors YuZheng Xie, Manoj Gupta, Arun Paramekanti, Tanusri Saha-Dasgupta

Quantum Gases · Cross-listed from quant-ph

Trapping 11,000 Atoms in a Tweezer Array Generated by a Single Metasurface

Yuqing Wang, Zhongchi Zhang, Tao Zhang et al. (+14 more)

The scalability of physical qubit numbers is a central challenge toward a universal fault-tolerant quantum computer. The inherent scalability of atom array quantum computers stems from the identical nature of atomic qubits, so the available qubit resource is primarily limited by the number of atoms that can be trapped and controlled. Here, we robustly trap 11,000 individual atoms in a tweezer array, thereby enabling the available qubit resource to reach the tens-of-thousands scale for the first time among all quantum computation platforms. This advance is enabled by a single metasurface, approximately 2 cm in diameter, that generates the entire tweezer array without the need for microscope objectives, thereby maximizing laser-power efficiency. The large aperture ensures a working distance of about 1.5 cm, allowing the metasurface to be placed outside the vacuum cell and avoiding the technical complications of in-vacuum operation. We further characterize the randomly loaded atom array using the statistical theory of percolation phase transitions. This work takes an important first step toward a quantum computer at the 10,000-qubit scale.
Read the full abstract

All authors Yuqing Wang, Zhongchi Zhang, Tao Zhang, Yuxuan Liao, Hanteng Wang, Ye Tian, Binjie Ji, Yujia Wu, Luming Ma, Chen Qing, Chengshu Li, Wei Zhang, Yidong Huang, Wenjun Zhang, Xue Feng, Wenlan Chen, Hui Zhai

Quantum Gases

A mean-field description of strong-to-weak symmetry breaking in the monitored Bose-Hubbard model

Yicheng Tang, Pradip Kattel and J. H. Pixley

Strong-to-weak spontaneous symmetry breaking has emerged as a novel form of ordering in monitored and open quantum systems, yet its characterization has so far primarily relied on nonlocal diagnostics. Here, we develop a Gutzwiller mean-field framework for monitored bosonic lattice systems, enabling the direct simulation of stochastic measurement dynamics in three spatial dimensions. Applying this approach to the monitored Bose-Hubbard model with local density measurements and Lindbladian dissipation, we identify strong-to-weak symmetry breaking through a trajectory-averaged local order parameter. We find that this local order parameter becomes critical near the critical measurement strength as the charge-sharpening transition. Both transitions exhibit a dynamical exponent $z=2$ in the dilute limit with a correlation length $\nu\simeq 0.6$, comparable to that of the charge-sharpening transition, suggesting that the two phenomena may originate from a common underlying critical point. Our work shows a local characterization of strong-to-weak symmetry breaking, reveals its connection to charge sharpening, and provides concrete predictions for future experiments on the monitored Bose-Hubbard model.
Read the full abstract

Disordered Systems and Neural Networks

Irregular Metamaterial Networks

Thomas P. Wytock, Chiara Daraio, Heinrich M. Jaeger et al. (+4 more)

Metamaterials can achieve exceptional functionality through careful engineering of their mesoscale structure. Although appropriately introduced irregularities can be advantageous, current approaches largely conform to regular structures to preserve tractability. Here, we contend that network theory, enriched with geometry and physics, provides a natural framework for designing metamaterials with controlled irregularities at relevant scales, thereby enabling the discovery of new property-enhancing structures. We examine how this augmented network theory can facilitate the creation of irregular metamaterials with enhanced or novel properties and how metamaterial research, in turn, is opening new directions in network science. Supported by machine learning and advanced self-assembly, the emerging field of irregular metamaterial networks is poised to transform inverse design and scalable manufacturing of novel materials.
Read the full abstract

All authors Thomas P. Wytock, Chiara Daraio, Heinrich M. Jaeger, Christopher A. Schuh, Lorenzo Valdevit, Vincenzo Vitelli, Adilson E. Motter

Superconductivity

Dynamical Josephson Effect Between a Singlet and a Triplet Superconductor

Morten Amundsen, Niladri Banerjee and Igor Žutić

Phase-sensitive Josephson effect has long been central to identifying unconventional pairing symmetries in superconductors. Although the selection rules governing Josephson junctions (JJs) are generally determined by the symmetries of the constituent superconductors, we demonstrate that this paradigm is modified in the dynamic regime. By modeling a JJ where spin-singlet and spin-triplet superconductors are separated by a two-dimensional electron gas, we show that a time-dependent gate voltage qualitatively changes the underlying selection rules. This modification arises as a consequence of the gate-controlled spin-orbit coupling. A harmonic modulation of the gate voltage generates an oscillatory $\cos \phi$ Josephson component which vanishes in the static limit. The resulting charge current contains both dissipationless and dissipative components, with the latter strongly suppressed at low temperatures. This dynamical Josephson effect could transform the use of JJs in qubits, as sources of spin-triplet currents, and as platforms for proximity effects.
Read the full abstract

Disordered Systems and Neural Networks

Neural Networks and Schramm-Loewner Evolutions

Neilesh Shrotri and Vlad Margarint

In this manuscript, we explore the application of neural networks to predict the natural parameter $\kappa \geq 0$ of Schramm-Loewner Evolution (SLE$_\kappa$) theory. SLE$_\kappa$ is a family of random fractal curves that has significant implications in Statistical Mechanics and Conformal Field Theory. This parameter $\kappa \geq 0$ plays an important role in the theory as there are models of Planar Statistical Physics that are proven to have SLE as scaling limits as well as others that are conjectured to have this limit for various choices of the parameter $\kappa \geq 0$. In addition, there are three different statistical behaviors of the SLE curves as the parameter $\kappa$ changes in $[0, \infty).$ Leveraging the powerful pattern recognition capabilities of neural networks, this study aims to develop a predictive model that can estimate the $\kappa$ parameter with good accuracy.
Read the full abstract

Superconductivity

Giant Resonances in Superconducting Films Induced by Nonsuperconducting Layers

D. André Orna T., Mauro M. Doria, Daniel Reyes et al. (+4 more)

We find that commensurate resonances in superconducting films endowed with a $SISIS$ structure, where $S$ and $I$ stand for superconducting and insulating layers, respectively, enhance the gap to a value three to four times the bulk gap. Such resonances rely on spatially localized quantum states that arise due to the commensurability between the total film thickness and the distance between the two insulating barriers. Our results are obtained in the context of the Bogoliubov-de Gennes equations within the Anderson approximation, applied here to Bi films, where quantum size effects are possible due to the abnormally large mean free path.
Read the full abstract

All authors D. André Orna T., Mauro M. Doria, Daniel Reyes, Isaías G. de Oliveira, Arkady Shanenko, Alexei Vagov, Y. T. Xing

Quantum Gases · Cross-listed from quant-ph

Probing information theoretic measures of nonlinear ultracold quantum gases using phase-space distributions

Mariyah Ughradar, Ramkumar Radhakrishnan, Siddharth Kumar Tiwari et al. (+1 more)

We use phase space distributions, specifically the Wigner and Husimi quasi probability distributions, to study harmonically trapped Bose–Einstein condensate described by the Gross Pitaevskii equation. From the mean field ground state wavefunction we construct both distributions and their position and momentum space marginals and we use these to compute a comprehensive set of information theoretic measures: Shannon, Wehrl, and Rényi entropies; Fisher information; cumulative and cross cumulative residual entropies; mutual information; and Kullback–Leibler, Jeffreys, Cauchy Schwarz, and Rényi divergences. Studying these quantities as a function of the $s$-wave scattering length for a representative Rb-85 condensate, we find that stronger repulsive interactions drive increased phase space delocalization, seen by a monotonic growth of Shannon and Wehrl entropies, while the Fisher information shows the complementary trend – increasing in position space and decreasing in momentum space in a manner consistent with the global Fisher uncertainty bound. Rényi entropies and divergence measures further reveal a systematic suppression of non classical interference and a shift toward more classical phase space structure in moving from the Wigner to the Husimi representation, with Wigner and Husimi based mutual informations converging at larger interaction strength. We note that, because the Gross Pitaevskii framework treats the many body state as a mean field product, the mutual information computed here quantifies statistical dependence between the conjugate phase space variables of the effective one body distribution rather than genuine particle particle entanglement.
Read the full abstract

All authors Mariyah Ughradar, Ramkumar Radhakrishnan, Siddharth Kumar Tiwari, Vikash Kumar Ojha

Quantum Gases · Cross-listed from physics.atom-ph

A Mid-Infrared Platform Based on Strontium Tweezer Arrays

Aaron Holman, Ximo Sun, Bojeong Seo et al. (+8 more)

Subwavelength atomic tweezer arrays, in which atoms can be positioned at distances smaller than their emission wavelength, have been proposed as a versatile platform to study collective emission phenomena, such as superradiance and subradiance. Experimentally, the realization of such arrays has been a challenge as typical emission wavelengths in the visible or near-infrared are short compared to typical tweezer spacings in the micrometer range. Here, we use $^{88}$Sr atoms in optical tweezer arrays to access a mid-infrared transition at 2,923 nm ($5s5p\:^{3}P_{2} \rightarrow\, 5s4d\:^{3}D_{3}$). We identify a magic trapping wavelength at 597.14(3) nm and demonstrate single-atom preparation and imaging with high fidelity. In addition, using 2,923 nm light, we demonstrate resolved-sideband cooling of tweezer-trapped strontium. Beyond enabling studies of collective emission phenomena in flexible arrangements of atoms, our platform opens novel opportunities for dipolar many-body physics and enhanced control over Rydberg dynamics and the strontium fine-structure qubit.
Read the full abstract

All authors Aaron Holman, Ximo Sun, Bojeong Seo, Joshua Corn, Zezheng Zhu, Yuan Xu, Jiahao Wu, Nanfang Yu, Dmytro Filin, Marianna Safronova, Sebastian Will

Statistical Mechanics · Cross-listed from quant-ph

Strong-to-Weak Spontaneous Symmetry Breaking

Chong Wang

Strong-to-weak spontaneous symmetry breaking (SW-SSB) has recently emerged as a useful framework for studying phases of matter in open systems, quantum or classical. Beginning with the simple idea of extending symmetry breaking to general mixed states, and the familiar equivalence between canonical and grand-canonical ensembles in statistical mechanics, the concept has grown into a unifying perspective connecting many different ideas in physics, including topological orders, emergent hydrodynamics, and information-theoretic characterization of phases of matter. This review provides a bird's-eye view of some of these recent developments.
Read the full abstract

Strongly Correlated Electrons

Reduce dimensional quantum criticality for Non-Fermi liquids

Phumudzo T. Rabambi and Mario Solís

We present a reduced dimension theoretical framework for studying quantum field theories at finite density, providing a tractable model for investigating non-Fermi liquid (NFL) behavior near quantum phase transitions. Our approach departs from the standard paradigm by placing bosons and fermions in different spatial dimensions: bosonic fields reside in a $(d+1)$-dimensional bulk, while fermionic fields are confined on a $d$-dimensional boundary. This dimensional separation significantly simplifies the renormalization group (RG) analysis of gapless boson-fermion coupling. We demonstrate that the tree-level boson exchange contributions, which typically exhibit logarithmic divergences, become finite in our reduced-dimension scheme. Furthermore, the $\log^2$ and $\log^3$ divergences that characterize 1-loop four-fermion interactions in conventional treatments are reduced to logarithmic divergences within this framework, substantially improving the convergence properties of the perturbative expansion and allowing controlled theoretical analysis of NFL physics.
Read the full abstract

Materials Science

Symmetry-Protected Weyl Nodal Loops in a Triangular Altermagnet

Chao-Chun Wei, Xiaoyin Li, Sophia Adams et al. (+9 more)

Weyl semimetals and altermagnets represent two distinct classes of quantum materials exhibiting nontrivial topological and magnetic order, respectively. Here we report the realization of a Weyl nodal-loop altermagnet in Cr$_7$Se$_8$, combining neutron diffraction and first-principles calculations. The hexagonal system hosts a coplanar $120^\circ$ compensated magnetic order on a triangular lattice, which breaks inversion-time-reversal and translation-time-reversal symmetries simultaneously while preserving a crystalline mirror plane. The resulting electronic structure features linearly dispersing nodal loops close to the Fermi level ($E_F$) confined to the mirror-invariant $k_z=0$ plane. Along high-symmetry directions, the crossings near $E_F$ form Dirac-like fourfold degeneracies in the absence of spin-orbit coupling; at generic momenta, these crossings split into twofold and form continuous Weyl-like nodal loops protected by mirror symmetry. The momentum-dependent spin polarization exhibits an $f$-wave-like pattern characteristic of odd-parity altermagnets.
Read the full abstract

All authors Chao-Chun Wei, Xiaoyin Li, Sophia Adams, Jacob Kjeldahl Jensen, Qiang Zhang, Jue Liu, Maxim Avdeev, Dinesh Kumar Yadav, Vikram V. Deshpande, Luisa Whittaker-Brooks, Feng Liu, Huiwen Ji

Disordered Systems and Neural Networks

Frustrated neurons: Energy landscapes and relaxation dynamics in repulsive phase oscillators

Brandon B. Le

Geometrical frustration, a central paradigm in condensed matter physics, provides a unifying language for systems in which locally preferred interactions cannot be made globally compatible. Here, we use this language to formulate a minimal theory of frustrated neural timing, mapping repulsively coupled rhythmic units onto antiferromagnetic XY models. Within this framework, the condensed-matter concepts of local constraints, degenerate ground-state manifolds, metastability, and quench dynamics become a concrete diagnostic framework for structured neural phase dynamics. We analyze a hierarchy of geometries: a triangle as the minimal frustrated motif with two chiral 120{\deg} timing states, a tetrahedron whose reduced ground-state manifold consists of intersecting continuous branches associated with antipodal pairings, and a kagome lattice on which local constraints define a constrained three-coloring manifold. The kagome lattice reveals the central dynamical result: zero-temperature relaxation suppresses global synchrony but typically selects low-energy metastable torque-balanced states rather than exact ground states. Finally, we show how the phase theory can be carried back towards biophysical neural models by treating it as an effective-interaction target, where geometrical timing frustration is realized through preferred phase lags that become incompatible around closed motifs. This perspective suggests that weak global coherence in neural systems does not necessarily signal disordered activity, but can reflect structured local timing order shaped by a frustrated dynamical landscape.
Read the full abstract

Materials Science

Towards Automated Discovery: A Review of Generative Models, Multimodal Learning and Closed-Loop Workflows in Inverse Materials Design

Anand Babu, Rogério Almeida Gouvêa and Gian-Marco Rignanese

Inverse materials design is shifting materials discovery from forward prediction toward targeted proposal of candidates that satisfy objectives under physical constraints. Here, we review advances in generative crystal structure modeling, multimodal learning, and closed-loop design pipelines for crystalline solids. We survey how generators learn chemical-structural priors from databases to enable controllable sampling of periodic structures, comparing variational autoencoders, normalizing flows, autoregressive models, and diffusion models. Across these families, we examine where feasibility constraints and physical priors enter, from representations and training objectives to sampling-time guidance, screening, and relaxation. We also discuss multimodal learning combining crystal structures, thermodynamic and electronic information, microscopy, spectroscopy, processing context, and scientific text to construct materials representations. Inverse-design strategies integrating conditional generation with latent optimization, Bayesian optimization, reinforcement learning, and active learning are also examined. We highlight recurring failure modes, including surrogate exploitation, diversity collapse, distribution shift, and the stability-synthesizability gap, and outline evaluation based on validity, novelty, uniqueness, stability, and cost. To support credible claims, we define a nine-rung discovery-credibility ladder and propose a minimum reporting standard: declared matching tolerances and database snapshots; separate reporting of uniqueness, training-set memorization, and external rediscovery; novelty as a continuous distance distribution; energy-above-hull distributions with functional and hull version; relaxation-survival and dynamical stability rates; and validation cost per credible hit. Headline validity or S.U.N. rates without these disclosures should be treated as uninformative.
Read the full abstract

Statistical Mechanics · Cross-listed from quant-ph

Spatial and particle-particle entanglement in 1D quantum walks of two distinguishable or indistinguishable bosonic particles

Christopher Mastandrea and Chih-Chun Chien

We present entanglement measures between spatially separated regions and between two distinguishable or indistinguishable particles in one-dimensional two-particle continuous-time quantum walks governed by the Hubbard Hamiltonian. The left-right entanglement checks the entropy of coarse-grained states counting the numbers of particles on the left and right halves of the lattice while the particle-particle entanglement is based on the entropy of the singular values of the time-evolved Fock state. With separable, entangled, and doubly occupied initial states, we examine initial entanglement and the following growth in different entanglement measures. While the entanglement measures of the indistinguishable cases resemble those of the distinguishable cases when the initial states are comparable, the long-time limits of the entanglement measures are typically non-monotonic as the onsite repulsion increases. We also discuss possible implications for future research of entanglement in multi-particle quantum dynamics.
Read the full abstract

Strongly Correlated Electrons

Electrical observation via spin Seebeck effect of fractionalized excitations in a magnetic insulator

Nan Tang, Josef Willsher, Stephan Glamsch et al. (+9 more)

Fractionalized excitations are among the most striking signatures of emergence in quantum matter. While widely sought in frustrated magnets, their detection and characterization remain challenging, motivating the exploration of new probes. Meanwhile, Spintronics offers versatile tools for probing spin-related phenomena. In particular, the spin Seebeck effect (SSE) converts thermally driven magnetic excitations into a voltage in an adjacent metal, providing electrical access to the underlying dynamics and transport properties. Here we employ the SSE to probe emergent magnetic monopoles in the non-collinear Ising magnet Dy$_2$Ti$_2$O$_7$, a rare instance of a three-dimensional fractionalized magnet. We observe an SSE signal featuring a pronounced peak at monopole proliferation, accompanied by characteristic frequency and angular dependence. Our results broaden the scope of spintronic methods for detecting exotic excitations, provide new insights into magnetic insulators generally and monopole physics specifically, and suggest the potential of quantum materials as functional interfaces.
Read the full abstract

All authors Nan Tang, Josef Willsher, Stephan Glamsch, Aisha Aqeel, Ludwig Scheuchenpflug, Michael Schulze, Christoph Liebald, Daniel Rytz, Christo Guguschev, Manfred Albrecht, Roderich Moessner, Philipp Gegenwart

Quantum Gases · Cross-listed from physics.atom-ph

Creating and Probing Spin-Squeezed States of Molecules

Connor M. Holland, Callum L. Welsh, Yukai Lu et al. (+4 more)

Polar molecules are a promising platform for quantum-enhanced sensing and precision tests of fundamental physics, owing to their strong long-range dipolar interactions, broad sensitivity to electromagnetic fields, and sensitivity to potential physics beyond the Standard Model. However, the creation of metrologically useful entangled states in molecular systems has remained elusive. Here, we report the first observation of a class of metrologically useful entangled states - spin-squeezed states - in polar CaF molecules trapped in an optical tweezer array. The spin degree of freedom is encoded in rotational levels which are directly coupled by dipolar exchange interactions. By harnessing appropriate dynamical decoupling schemes we observe up to 3.0(3)dB of metrological gain, (2.2(3)dB without measurement correction) from direct exchange interactions. Using Floquet engineering, we further realize richer Hamiltonians that preserve spin squeezing while enabling the development of longer-range quantum correlations. Using site- and spin-resolved measurements we demonstrate that these entangled states enhance sensitivity to both homogeneous and spatially varying fields, and reveal strong non-classical correlations, including bipartite entanglement and Einstein-Podolsky-Rosen steering. Finally, we transfer the spin-squeezed states into long-lived and non-interacting hyperfine states, where the metrological enhancement persists for up to 100ms. Our results establish molecular optical tweezer arrays as a scalable platform for generating, controlling, characterizing, and storing entangled states of molecules, opening new opportunities for quantum-enhanced sensing and precision tests of fundamental physics.
Read the full abstract

All authors Connor M. Holland, Callum L. Welsh, Yukai Lu, David Wellnitz, Xing-Yan Chen, Ana Maria Rey, Lawrence W. Cheuk

Quantum Gases

Thouless Pumping of Large Chern Numbers in Optical Floquet Quasicrystals

Shien Wan, Zecheng Li and Bo Song

Chern numbers are central to correlated and topological phenomena, yet most topological systems are associated with Chern numbers of order unity. Here we propose a scheme to achieve large Chern numbers in an optical Floquet quasicrystal with cold atoms, which can be directly measured via Thouless pumping. We study the quasienergy spectrum of Floquet quasicrystals and characterize the emergent Chern numbers using gap labeling theorem. We further investigate the Thouless pumping in the Floquet quasicrystal at different driving frequencies and amplitudes, revealing the connection between transport features and the quasienergy spectrum. Our findings open new avenues for exploring rich topological dynamics in Floquet quasicrystals and realizing fractional Chern insulating states.
Read the full abstract