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Physics Condensed Matter

cond-mat Watch Condensed Matter

Tuesday 2 June

Strongly Correlated Electrons

Quantum String Interactions Revealed by Full Counting Statistics

Chang-Yan Wang and Xue-Feng Zhang

How quantum strings interact is a basic question for extended objects in quantum many-body physics. Even the simplest hard-core constraint (no crossing), can generate a nontrivial effective potential, whose microscopic form is difficult to determine because the relative distance between the strings is intrinsically nonlocal. Here we show that this nonlocality is naturally captured by full counting statistics (FCS). For two hard-core quantum strings, we derive an analytic FCS expression for the emergent interaction by identifying the virtual process in which the two strings touch and hop back. Using the FCS–entanglement relation, we find the effective potential has the entanglement-controlled asymptotic form $\ln\Delta E(r)\sim -\pi^2 r^2/(12 S_\ell)$ up to subleading terms, where $S_\ell$ is the entanglement entropy between the two halves of a quantum string. We confirm the theory using high-precision numerical calculations and finite-size FCS estimates. Our results reveal FCS as a direct route to effective interactions between quantum topological line-defects, which may also be extended to higher-form charge.
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Statistical Mechanics · Cross-listed from hep-th

Coarse graining from within: Wilson-Fisher universality on $S^3$

Alfio M. Bonanno, Renata Ferrero and Giovanni Oglialoro

Wilsonian renormalization is usually formulated in momentum space, but on curved backgrounds momentum shells have no invariant meaning. We replace them by an intrinsic spectral cutoff, ordering modes by the covariant Laplacian and setting the cutoff resolution by the system size in renormalization group (RG) units. For a scalar field on $S^3$, this yields a covariant, momentum-free RG flow whose trace is an exact sum over spherical harmonics. The standard flat-space flow is recovered when the sphere is large compared with the coarse-graining scale. As a nontrivial test, the compact spectral flow realizes Wilson-Fisher universality without momentum shells: the interacting fixed point survives at finite resolution, has one relevant direction, and approaches its flat-space counterpart smoothly, with critical exponents only weakly affected by the compact spectrum.
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Quantum Gases · Cross-listed from quant-ph

Quantum error correction with the toric code

Atom Computing and Collaborators

Quantum computing platforms based on arrays of tweezer-confined neutral atoms have recently emerged as a competitive modality thanks to a direct path toward high qubit count, rapidly advancing operation fidelities, and their ability to execute circuits with arbitrary qubit connectivity. These features will enable the use of efficient error correction schemes with high encoding-rates, time-efficient decoding, and resource-efficient architectures based on transversal gates. With these goals in mind, recent state of the art neutral atom demonstrations focus on the transition from the use of physical qubits to error-corrected logical qubits, but to date there has been no demonstration of repeated error correction scalable to arbitrary depth. Here, we demonstrate many cycles of syndrome extraction in a toric quantum error correcting code, using mid-circuit measurement and replacement of lost qubits, including reloading of a qubit reservoir for indefinite coherent operation. We characterize the logical error rate after up to 90 cycles, showing that logical information can be preserved through multiple rounds of qubit reloading. Comparing two distances of the code up to 8 rounds of syndrome extraction shows a lower absolute logical error rate for the larger distance code.
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Mesoscale and Nanoscale Physics

Multiparametric Quantum Sensing of Liquids Using NV Centres and Tethered Magnetic Nanoparticles

Johannes Fiedler, Martin Møller Greve and Justas Zalieckas

We propose a new concept for non-invasive, multiparametric liquid analysis based on nitrogen-vacancy (NV) centre magnetometry, relaxometry and surface-tethered magnetic nanoparticles. Magnetic nanoparticles are anchored to a diamond surface via DNA strands, forming nanoscale mechanical oscillators whose thermally driven motion is strongly influenced by the surrounding liquid environment. The resulting time-dependent magnetic fields couple to near-surface NV centres and are detected via optically detected magnetic resonance or changes in spin coherence time. By spatially patterning the diamond surface with regions functionalised by DNA tethers of different lengths, sequences, or chemical modifications, a single liquid is mapped onto a high-dimensional quantum response vector rather than a single scalar observable. Changes in viscosity, molecular adsorption, or chemical interactions modify the dynamics of magnetic nanoparticles in a region-specific manner, enabling differential sensing across the surface. We outline the physical transduction mechanism, discuss relevant scaling relations, and assess experimental feasibility using established wide-field NV magnetometry and relaxometry methods. The proposed platform combines quantum sensing with surface heterogeneity, offering a versatile route toward parallel, label-free liquid characterisation.
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Materials Science

Uncertainty-Aware Symbolic Regression through Bayesian Support Selection

Satadeep Bhattacharjee

The Sure Independence Screening and Sparsifying Operator (SISSO) framework is a powerful symbolic-regression method for extracting compact and interpretable descriptors from large nonlinear feature spaces. However, standard SISSO is deterministic: it returns a single descriptor and point prediction, without quantifying uncertainty in descriptor selection, regression coefficients, or predictions. Here we introduce a probabilistic extension in which the sure independence screening (SIS) stage is kept deterministic to preserve scalability, while the sparsifying operator (SO) stage is reformulated as Bayesian inference over the SIS-screened support space. The resulting deterministic-SIS/Bayesian-SO framework yields posterior probabilities for competing descriptor supports, feature-inclusion probabilities, Bayesian-model-averaged predictions, and predictive credible intervals, while recovering the deterministic SO descriptor of standard SISSO in the maximum-a-posteriori limit. Applied to an $X_2YZ$ Heusler-alloy magnetic-moment dataset, the approach gives modest improvements in five-fold cross-validation RMSE and near-nominal empirical coverage of the 95$\%$ predictive intervals. More importantly, the posterior exposes competing, physically related symbolic descriptor families that would appear artificially unique in a deterministic analysis. These results suggest that deterministic-SIS/Bayesian-SO can be used as an uncertainty-aware diagnostic extension of SISSO: a tool for assessing descriptor confidence, stability, and non-uniqueness in small-data materials regression problems.
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Superconductivity

Bipolar-doped superconducting infinite-layer cuprates

Fengzhe Wang, Yueying Li, Heng Wang et al. (+9 more)

Distilling the intrinsic physics of the superconducting CuO2 plane from the complexities of charge-reservoir layers is a defining challenge in high-temperature superconductivity. While superconducting electron-doped infinite-layer cuprates have been synthesized, controllable and uniform hole doping has long remained elusive despite exploratory attempts, limiting spectroscopic insights. Here, we realize bipolar doping across infinite-layer (Sr,Eu)CuO2 and (Ca,Li)CuO2+{\delta} single-crystalline thin films, mapping the electronic phase diagram. Both electron- and hole-doped films show pronounced electrical resistance anisotropy, indicating the quasi-two-dimensional nature of the CuO2 planes. Angle-resolved photoemission spectroscopy across electron- and hole-doped regimes reveals persistent antiferromagnetic band folding coexisting with superconductivity. Remarkably, at a hole doping ~0.07 determined by Luttinger volume, the antiferromagnetic folding emerges from Fermi arcs within the film's single Fermi surface, with the onset superconducting transition temperature exceeding 60 K. These findings redefine the interplay between magnetic order and superconductivity and establish a definitive platform to investigate the intrinsic mechanism of high-temperature superconducting cuprates.
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All authors Fengzhe Wang, Yueying Li, Heng Wang, Lizhi Xu, Xianfeng Wu, Lixiang Xu, Guangdi Zhou, Jin-Feng Jia, Peng Li, Haoliang Huang, Qi-Kun Xue, Zhuoyu Chen

Materials Science

Topological Weyl Phase of an Ideal Spin-Gapless Semiconductor KCrSe

Subhajit Mandal, Bishal Das, Himanshu Sharma et al. (+2 more)

The coexistence of topological and spin-polarized electronic states within a single material platform provides an attractive route toward emergent quantum phenomena and spintronic functionalities. However, materials simultaneously exhibiting spin-gapless semiconducting (SGS) behavior and Weyl semimetallicity remain exceedingly rare. Here, using first-principles calculations, we identify the half-Heusler compound KCrSe as an ideal spin-gapless Weyl semimetal. Transport calculations reveal a weak temperature dependence of the longitudinal conductivity and relatively small Seebeck coefficients, providing further evidence of its SGS nature. KCrSe hosts a single pair of Weyl nodes-the minimum number permitted in a Weyl semimetal-located in close proximity to the Fermi level (E$_\text{F}$), resulting in exceptionally clean bulk and surface electronic spectra. The nontrivial Berry curvature associated with these Weyl nodes gives rise to sizable anomalous transport responses, including an anomalous Hall conductivity of $\sigma_{xy}^{A}\sim 90.76~\mathrm{S\,cm^{-1}}$ and an anomalous Nernst conductivity of $\alpha_{xy}^{A}\sim 0.15~\mathrm{A\,m^{-1}K^{-1}}$ at E$_\text{F}$, with substantially enhanced values at lower energies. The combination of an ideal Weyl topology, fully spin-polarized low-energy states, and finite anomalous transport establishes KCrSe as a promising platform for designing high-efficiency topological spintronic devices.
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All authors Subhajit Mandal, Bishal Das, Himanshu Sharma, Satoru Hayami, Aftab Alam

Statistical Mechanics · Cross-listed from quant-ph

Operator spreading in random unitary circuits with orthogonal/symplectic-invariant gate distributions

Zhiyang Tan and Piet W. Brouwer

We investigate operator spreading in random quantum circuits with gates drawn from orthogonal-invariant or symplectic-invariant ensembles, revealing several key distinctions from the well-studied unitary-invariant case. We find that the ensemble-averaged Pauli-string weights relax to a ternary-valued structure, instead of the binary structure of unitary-invariant circuits. For orthogonal- or symplectic-invariant circuits, the domain wall separating trivial and scrambled regions has a finite width even for Haar-random gates, whereas domain walls are sharp for Haar-distributed random unitary circuits. We further find a fundamental dichotomy between random circuits with two-qubit gates from the two disconnected components of the orthogonal group: While the butterfly velocity for the special orthogonal ensemble lies between zero and the Haar value, the negative-determinant sector exhibits a non-zero lower bound for any gate distribution. Moreover, for qudit size $q=2$, the butterfly velocity can exceed that of the Haar-random ensemble.
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Soft Condensed Matter

Emergent cohesion via self-caging in maximally entangled rod packings

Yeonsu Jung and L. Mahadevan

Random packings of disordered rigid rods exhibit emergent cohesion, as exemplified in a nest of twigs that is self-equilibrated, free-standing structures. We analyze the geometric motif underlying this cohesion using a rod packing that maximizes the average crossing number subject to non-penetration constraints. We show that this protocol leads to self-caging: collective geometric constraints that prevent rod escape even in finite systems with free boundaries, leading to packings that remain mechanically cohesive due to a combination of purely repulsive and frictional interactions. We show that self-caging is controlled by the available free-volume in translational and rotational configuration spaces, which is minimal when $N/(Z\alpha)=1/3$ where $N$ is the number of rods, $\alpha$ is the aspect ratio, and $Z$ is the average coordination number. Our results establish a minimal geometric motif for entanglement-induced cohesion in athermal rod packings, with implications for cohesive granular matter without attractive forces.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Coexistence of dipolar and quadrupolar higher-order topology

Konstantin Rodionenko, Maxim Mazanov and Maxim A. Gorlach

Two-dimensional higher-order topological insulators are typically classified either as dipolar or quadrupolar depending on the relevant invariant. These two classes were previously considered non-overlapping. Here we put forward an example system exhibiting dipolar and quadrupolar higher-order topology simultaneously, suggest its implementation using the arrays of laser-written evanescently coupled optical waveguides and support our conclusions by the full-wave numerical simulations.
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Mesoscale and Nanoscale Physics

Emergent Hall viscosity in the integer quantum Hall phases of graphene-like systems

M. Selch and M. A. Zubkov

We explicitly distinguish Hall viscosity as defined relative to the strain field vs. relative to an emergent vielbein or metric field and discuss it for graphene-like systems. Aside from the gravitational or vielbein/metric related “geometric” Hall viscosity prevailing throughout the literature, a contribution proportional to the Hall conductivity, the “electronic” Hall viscosity, due to the emergent strain induced gauge field exists. We unify both contributions within the “emergent” Hall viscosity, determine it explicitly for graphene in the semimetal and Semenoff semiconducting phases, and in the latter case compare it to its non-relativistic limit. Under these circumstances two topological invariants enter the emergent Hall viscosity in the presence of translation and rotation symmetries. We employ Green function representations for the electronic Hall viscosity, quantized rather generically, and the geometric Hall viscosity, the latter being valid only under Lorentz (or Galilean) symmetry. We discuss experimental perspectives for extracting the emergent Hall viscosity.
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Other Condensed Matter · Cross-listed from quant-ph

Practical gates by Majorana fermion motion

Yuri D. Lensky, Bryce Kobrin, Kostyantyn Kechedzhi et al. (+1 more)

Quantum error correction protocols protect against local errors by storing logical information non-locally. This poses a challenge: how to design efficient logical gates on the non-local “hidden” logical information, and how to implement these gates using the local physical operations. We develop a general description of planar Pauli stabilizer codes and protocols for logical operations in terms of point-like particles called Majorana fermions. Information is stored in the pairwise fermion parities of spatially separated Majorana fermions. The description in terms of Majorana fermions captures not only large distance asymptotics, but also all scales down to the lattice constants. We exploit this locality to densely pack logical information in spacetime. The simplest application is to a static case: dense memory. More importantly, we implement fault-tolerant Majorana motion and leverage this primitive to design braiding-based logical gates. This approach reduces space overhead of logical operations resulting in an improved logical error rate given fixed number of physical qubits. We illustrate a practical use of our approach by designing and benchmarking of 2-qubit Clifford gates. We find numerically that our protocol outperforms lattice surgery in this setting for near-term error rates and realistic device constraints. More generally, introduction of compact motion of Majorana fermions as an efficient computational primitive opens a promising new route for the design of low overhead error correction protocols.
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All authors Yuri D. Lensky, Bryce Kobrin, Kostyantyn Kechedzhi, Igor Aleiner

Strongly Correlated Electrons

Spin-chiral electron-phonon coupling in metallic strontium titanate

N. Somun, L. Rogić, I. Khayr et al. (+12 more)

Electron-phonon coupling (EPC) - the interaction between conduction electrons and quantized atomic vibrations - plays a central role in condensed matter physics and determines some of the most important properties of materials, such as electrical resistivity and superconductivity. Conventionally, EPC is assumed to be induced by the ionic electrostatic background, and electronic spin plays no role in the process. In stark contrast with this view, here we uncover a direct spin-mediated coupling mechanism between electrons and transverse polar phonons in a metal. Using far-infrared light absorption measurements of the model system SrTiO$_3$ in a magnetic field, we observe a strong spin-mediated EPC that is quantitatively consistent with recent theoretical predictions, and that generates chiral phonon modes with large effective magnetic moments. The extracted coupling strength is in good agreement with ab initio estimates and sufficiently high to explain superconductivity in SrTiO$_3$, thereby resolving a long-standing conundrum. Spin-chiral EPC should generically appear in all metals with polar phonons, and the present work could be of relevance to spintronics applications and to uncovering the origins of superconductivity in layered materials, metals with Dirac points in their electronic dispersions, and nearly ferroelectric superconductors.
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All authors N. Somun, L. Rogić, I. Khayr, E. Tafra, M. Basletić, A. Kundu, J. Dzian, F. Le Mardele, M. Orlita, M. Greven, B. Büchner, A. Alfonsov, M. N. Gastiasoro, A. Klein, D. Pelc

Materials Science

Bernoulli principle in ferroelectrics

Anna Razumnaya, Yuri Tikhonov, Dmitrii Naidenko et al. (+2 more)

Ferroelectric materials, characterized by spontaneous electric polarization, exhibit remarkable parallels with fluid dynamics, where polarization flux behaves similarly to fluid flow. Understanding polarization distribution in confined geometries at the nanoscale is crucial for both fundamental physics and technological applications. Here, we show that the classical Bernoulli principle, which describes the conservation of the energy flux along velocity streamlines in a moving fluid, can be extended to the conservation of polarization flux in ferroelectric nanorods with varying cross-sectional areas. Geometric constrictions lead to an increase in polarization, resembling fluid acceleration in a narrowing pipe, while expansions cause a decrease. Beyond a critical expansion, phase separation occurs, giving rise to topological polarization structures such as polarization bubbles, curls and Hopfions. This effect extends to soft ferroelectrics, including ferroelectric nematic liquid crystals, where polarization flux conservation governs the formation of complex mesoscale states.
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All authors Anna Razumnaya, Yuri Tikhonov, Dmitrii Naidenko, Ekaterina Linnik, Igor Lukyanchuk

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

Parametrically induced strong coupling between a superconducting quantum circuit and a solid-state spin ensemble

Alejandro E. Baptista, Jinwoong Kim, Sonia Rani et al. (+2 more)

Efficient quantum state transfer between superconducting circuits and solid-state spins would unlock high-coherence quantum memories for superconducting quantum processors. We demonstrate dynamically controlled strong coupling between a Josephson circuit and a rare-earth spin ensemble. Using a parametric pump, we realize on-demand coupling of several MHz, which will enable faithful state transfer between quantum circuits and spins. Our architecture enables quantum control of spin ensembles, and paves the way for hybrid memories with coherence far beyond those of superconducting circuits alone.
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All authors Alejandro E. Baptista, Jinwoong Kim, Sonia Rani, Xi Cao, Wolfgang Pfaff

Soft Condensed Matter

Axial dispersion in dilute solutions of linear and branched polymers in parallel-plate and expansion-contraction microchannels

C. Levi Petix, Tzortzis Koulaxizis, Griffin D. Overton et al. (+2 more)

The axial dispersion of polymers in microchannels depends on an interplay between microchannel geometry, polymer architecture, and hydrodynamics. Here, we investigate the axial dispersion of linear, comb, and star polymers in parallel-plate and sinusoidal expansion-contraction microchannels at dilute concentrations using multiparticle collision dynamics simulations. The polymers all contain the same number of monomers but differ in their architecture, and their concentration is fixed at either one value that is dilute for all polymers or the same value relative to the overlap concentration for each polymer. The dispersion coefficients measured at a nominal solvent volumetric flow rate are found to depend on both architecture and concentration. We show that the dispersion coefficients collapse as a function of the Péclet number after accounting for confinement effects on the polymer diffusion coefficient and polymer contributions to the flow field, and the dispersion coefficients in the parallel-plate microchannel can be reasonably predicted using a theory that accounts for inhomogeneous distribution of the polymers in the microchannel.
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All authors C. Levi Petix, Tzortzis Koulaxizis, Griffin D. Overton, Antonia Statt, Michael P. Howard

Materials Science

Deciphering borophene growth pathways with data-driven simulations

Colin Bousige, Jean Furstoss, Julien Lam et al. (+1 more)

Deterministic synthesis of borophene remains challenging because many polymorphs compete during nucleation and growth. Here we combine a reactive machine-learned interatomic potential with grand-canonical Monte Carlo simulations and data-driven structural classification to track borophene formation from early nuclei to extended layers on Ag(111) and Ag(100). We build temperature-pressure substrate growth maps and resolve how vacancy motifs, phase intermixing and seed structure govern polymorph selection. The simulations reproduce key experimental trends, including the prevalence of $\beta_{12}$/$\chi_3$ phases and their temperature-dependent competition, while revealing kinetic pathways that connect metastable nuclei to long-range order. We identify conditions that suppress competing motifs and promote targeted phases, providing actionable synthesis windows. These results establish a predictive framework for directing borophene growth and, more broadly, for controlling polymorphism in low-dimensional materials by coupling atomistic simulation with machine-learning-enabled phase recognition.
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All authors Colin Bousige, Jean Furstoss, Julien Lam, Pierre Mignon

Mesoscale and Nanoscale Physics

20 Second Parity Lifetime in an InAs–Pb Tetron Device

Morteza Aghaee, Zulfi Alam, Mariusz Andrzejczuk et al. (+162 more)

A central promise of topological quantum computing is that increasing the excitation gap improves device performance significantly. Here, we experimentally validate this principle in an InAs–Pb tetron device via interferometric single-shot parity measurements. By replacing aluminum with the higher-gap superconductor lead in our superconductor-semiconductor hybrid devices, we have improved the robustness of our topological phase. In addition, to enable fast and precise bring-up at scale, we have developed an rf measurement technique that resolves low-energy wire-end states and directly measures their energy splitting with $\mu\text{eV}$ precision. We employ this technique to bring up a device in a multi-tetron array and perform parity measurements of one of the tetron's hybrid nanowires (NWs). By controllably switching the wire parity, we observe $h/2e$-periodic bimodal shifts in the quantum capacitance of a quantum dot coupled to the hybrid nanowire in an interference loop. Further time-resolved measurements reveal a characteristic parity switching time of $\sim 20$ s with some instances reaching minute-scale. Such extremely long parity lifetimes are orders of magnitude longer than typical qubit operation times, which are on the order of $\mu\text{s}$. Finally, we discuss potential implications for the fidelity of Pauli measurements.
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All authors Morteza Aghaee, Zulfi Alam, Mariusz Andrzejczuk, Andrey Antipov, Theodora Asimakidis, Mikhail Astafev, Lukas Avilovas, Ahmad Azizimanesh, Amin Barzegar, Bela Bauer, Jonathan Becker, Umesh Kumar Bhaskar, Andrea G. Boa, Srini Boddapati, Nichlaus Bohac, Jouri Bommer, Jan Borovsky, Léo Bourdet, Samuel Boutin, Srivatsa Chakravarthi, Benjamin J. Chapman, Nikolaos Chatzaras, Tzu-Chiao Chien, Jason Cho, Patrick T. Codd, William Cole, Paul W. Cooper, Fabiano Corsetti, Ajuan Cui, Tareq El Dandachi, Konstantinos Divanis, Clayton Doyle, Andreas Ekefjard, Javier A. Falcon, Saeed Fallahi, Luca Galletti, Geoffrey C. Gardner, Haris Gavranovic, João Pedro Morais Gomes, Deshan Govender, Flavio Griggio, Ruben Grigoryan, Sebastian Grijalva, Sergei Gronin, Jan Gukelberger, Marzie Hamdast, Esben Bork Hansen, Sebastian Heedt, Samantha Ho, Laurens Holgaard, Kevin van Hoogdalem, Jinnapat Indrapiromkul, Henrik Ingerslev, Lovro Ivancevic, Max Jantos, Thomas Jensen, Jaspreet Singh Jhoja, Vidul R. Joshi, Konstantin V. Kalashnikov, Ray Kallaher, Rachpon Kalra, Farhad Karimi, Torsten Karzig, Maren Elisabeth Kloster, Christina Knapp, Jonathan Knoblauch, Jonne Koski, Anders Kringhøj, Tom Laeven, Jeffrey Lai, Gijs de Lange, Thorvald W. Larsen, Kyunghoon Lee, Kongyi Li, Shuang Liang, Tyler Lindemann, Luna Lochmatter, Marijn Lucas, Roman Lutchyn, Morten Hannibal Madsen, Nasiari Madulid, Ivan Maliyov, Yanick Mampaey, Michael Manfra, Signe Brynold Markussen, Esteban A. Martinez, J. R. Mattinson, Mónica Meira, Camille A. Mikolas, Sarang Mittal, Gopakumar Mohandas, Christian Mollgaard, Michiel W. A. de Moor, Chris Moore, George Moussa, Bhargav Nabar, Anirudh Narla, Ahmad Naseri, Chetan Nayak, Bjørn Funch Schrøder Nielsen, Jens Hedegaard Nielsen, Michael J. Nystrom, Eoin O'Farrell, Keita Ohtani, Theodore Rex Orth, Sara Di Paolo, Camille Papon, Luca Petit, Dima Pikulin, Mohana Rajpalke, Alejandro Alcaraz Ramirez, Katrine Rasmussen, David Razmadze, Yuan Ren, Mariya Romanova, Loïc Roure, Ivan Sadovskyy, Lauri Sainiemi, Juan Carlos Estrada Saldaña, Irene Sanlorenzo, Tatiane Pereira dos Santos, Carl Vincent C. Saruda, Simon Schaal, John Schack, Emma R. Schmidgall, Christina Sfetsou, Cristina Sfiligoj, Zahra Shekason, Sarat Shankar Sinha, Patrick Sohr, Maria João Lourenço de Sousa, Kasper Roed Spiegelhauer, Tomas Stankevic, Henri J. Suominen, Judith Suter, Attila Szénási, Samuel M. L. Teicher, Naganivetha Thiyagarajah, Raj Tholapi, Mason Thomas, Dennis Tom, Emily Toomey, Joshua Tracy, Michelle Turley, Matthew D. Turner, Ivan Urban, Aakash Valliappan, Dmitrii V. Viazmitinov, Anna Wulff Viazmitinova, Dominik Johannes Vogel, Wenbo Wang, Christopher A. Watson, John Watson, Alex Webster, Joseph Weston, Timothy Williamson, Georg W. Winkler, David J. van Woerkom, Brian Paquelet Wuetz, Cécile X. Yu, Emrah Yucelen, Jesús Herranz Zamorano, Roland Zeisel, Guoji Zheng, A. M. Zimmerman

Strongly Correlated Electrons

Modification of Charge and Spin Textures by Light Chemical Substitution in Eu(Al$_{1-x}$Ga$_{x}$)$_4$ ($x=0.1$)

Zétény Bacsó, Fellipe Carneiro, Kevin Allen et al. (+6 more)

We present the results of a resonant X-ray diffraction experiment, resolving both charge and spin textures in the intermetallic topological magnet Eu(Al$_{1-x}$Ga$_{x}$)$_4$, $x$ = 0.1. Below $\approx$ 75 K the system develops a charge density wave (CDW) with propagation vector kCDW ~ (0, 0, 0.18). The CDW order parameter grows monotonically on cooling until ~ 15 K, when a sudden decrease in the CDW amplitude occurs. Pairs of magnetic satellites of the (0, 0, 8) Bragg reflection corresponding to two distinct domains, k = ($\pm \delta_\text{m}$, 0, 0), k2 = (0, $\pm\delta_\text{m}$, 0), $\delta_\text{m} = 0.2002(4)$ were studied at the Eu L3 edge, appearing below TN = 14.8 K. Our measurement of TN is exactly coincident with the sudden drop in the CDW amplitude, which suggests strong coupling between the charge and spin orders, as observed in other compounds of the Eu(Al$_{1-x}$Ga$_{x}$)$_4$ series. Azimuthal measurements revealed a single helical spin arrangement with an elliptical envelope of $\mu_\text{Y}/\mu_\text{Z}$ = 1.19(6) for the k2 domain, and a tilted helical (helicoidal) spin arrangement for the k1 domain, with $\mu_\text{Y}/\mu_\text{Z}$ = 1.14(4) and $\mu_\text{X}/\mu_\text{Z}$ = 0.20(2) that may be hidden for the k2 domain due to multiple subdomains. Temperature evolution of the magnetic satellite intensities in linear and circularly polarised light found the respective ratio to be invariant with temperature, suggesting a single magnetic phase below TN. This behaviour is unlike the x = 0 material, in which a spin density wave forms first, transitioning to a helical ground state on cooling through intermediate phases. Future theoretical work on the Eu electronic ground state, supported by related experiments, will help understand the effects of Ga substitution on the evolution of the magnetic structure.
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All authors Zétény Bacsó, Fellipe Carneiro, Kevin Allen, Aly H. Abdeldaim, Rebecca Scatena, Jaime M. Moya, Emilia Morosan, Alessandro Bombardi, Roger D. Johnson

Disordered Systems and Neural Networks · Cross-listed from quant-ph

Subspace-selective unitary manipulation based on the Hilbert-space symmetric structures in the multiple-quantum operator algebra spaces in the quantum-computing speedup theory

Xijia Miao

The quantum-computing speedup theory considers the symmetric structures and properties of quantum systems as the fundamental Quantum-Computing-Speedup (QCS) resources which are responsible for exponentially speeding up quantum computing and simulating. At present a large and important problem is how to make use of the fundamental QCS resources to speed up essentially quantum computing and simulating. Here the author makes a great effort toward solving this important problem. The theoretical research work in this paper is mainly divided into the two Parts I and II. The Part I investigates mainly the multiple-quantum operator algebra spaces. And the relationships are analyzed among the multiple-quantum operator algebra spaces, quantum simulating for the unitary time-evolutional processes, and the fundamental QCS resources which exist in the different kinds of basic quantum spaces: the multiple-quantum operator algebra spaces, the density operator spaces, and the Hilbert spaces. It concludes that the multiple-quantum operator algebra space must be positioned as the central place where the fundamental QCS resources are exploited to speed up quantum computing and simulating. The Part II investigates mainly the subspace-selective unitary manipulation based on the Hilbert-space symmetric structures. Recognize that the multiple-quantum operator algebra space is the central place. Then those fundamental QCS resources original from the Hilbert space (a quantum-state space) must be explicitly taken into account in the multiple-quantum operator algebra space (a linear operator space). This is an important problem. The subspace-selective unitary manipulation is able to solve this problem. It aims to harness the fundamental QCS resources original from the Hilbert space to speed up quantum computing and simulating in the multiple-quantum operator algebra space.
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Materials Science

Predicting core-level X-ray photoemission spectra of oxide surfaces from first principles – a case study for SnO$_2$

Wenxuan Cai, Stefan Kucharski, Chris Blackman et al. (+2 more)

X-ray photoemission spectroscopy (XPS) is a powerful technique to gain insight into the chemical properties of oxide surfaces. However, the interpretation of XPS spectra is notoriously difficult as realistic surfaces contain different terminations, reconstructions, adsorbates and defects all of which leave (potentially overlapping) spectroscopic fingerprints. To address this challenge, we present a first-principles approach based on the Z+1 method that allows us to predict XPS spectra of oxide surfaces which can directly be compared to experimental measurements. We present results for different SnO$_2$ (110) surfaces: the stoichiometric surface, surfaces with different types of vacancies (one of which is the fully reduced surface) and also the fully reduced surface with adsorbed OH and O$_2$ molecules. For these systems, we calculate the O 1s core-electron binding energies of all oxygen atoms and then use this to predict the XPS spectrum. We find that the fully reduced surface gives rise to a highly symmetric peak shape in agreement with recent XPS measurements. In contrast, the spectrum of the stoichiometric surface exhibits an additional feature at low binding energies caused by the bridging oxygen atoms at the surface. For the reduced surface with OH and O$_2$ adsorbates, the spectrum exhibits additional features at higher binding energies. The predicted spectra are in good agreement with experimental results obtained for reduced surfaces that have been exposed to oxygen gas. The presented method is general and can be straightforwardly applied to other surfaces.
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All authors Wenxuan Cai, Stefan Kucharski, Chris Blackman, Juhan Matthias Kahk, Johannes Lischner

Statistical Mechanics · Cross-listed from quant-ph

Generating quantum ensembles via reverse-time quantum diffusions

Maël Bompais, Mădălin Guţă and Juan P. Garrahan

We establish a reverse-time denoising theory for quantum diffusions of continuously measured quantum systems. Starting from the stochastic Schrödinger equation of a forward noising dynamics, we derive the exact reverse-time dynamics for quantum trajectories, whose law coincides with the time-reversal of the original process. We prove that the denoising dynamics is a physically admissible quantum diffusion, with the same measurement-induced noise but a state-dependent feedback Hamiltonian, a direct analogue of the "score function" of generative classical diffusion models. This provides a principled framework for converting samples of a simple distribution into those of a more complex ensemble of quantum states. We show how the denoising dynamics can be directly learnt from forward trajectory data, and how to exploit purification to initialise the denoising process.
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Materials Science

Quantitative Detection of Molecular Oxygen in the Gas Phase with Fluorescent Nanodiamonds

Nicholas A. Nunn, Antonin Marek, Alex I. Smirnov et al. (+2 more)

The quantitative detection of paramagnetic molecular oxygen (O2) in gas mixtures using optically detected magnetic resonance (ODMR) from negatively charged nitrogen-vacancy (NV-) centers in fluorescent nanodiamonds is described. Fluorescent nanodiamonds approximately 70 nm in diameter were deposited on the glass surface of a microfluidic channel, and the oxygen concentration varied from 0 to 100% (0 to 760 mmHg O2 partial pressure) by mixing O2 and N2 gases at ambient pressure. Continuous-wave (CW) ODMR contrast was measured using a double-modulation (lock-in) detection scheme applied to both optical excitation and microwave drives. The ODMR contrast decreases linearly with oxygen partial pressure, with a sensitivity coefficient k of (-10.1 +/- 0.3) x 10^-4 % mmHg^-1. The oxygen detection limit of the experimental setup was estimated to be approximately 8 mmHg O2 partial pressure (corresponding to about 1% O2 in the gas mixture). Cycling of the content of O2 in the gas mixture in the range of 0-5% revealed slight hysteresis and corresponding repeatability of 0.006 in percent ODMR contrast. The observed fluorescence quenching and relatively slow response (ranging from several to tens of minutes) upon changes in oxygen concentration suggest that physisorption of gas molecules on the nanodiamond surfaces contributes to equilibration dynamics. The applicability of the nanodiamond-based oxygen quantum sensor was further demonstrated by detecting transient bursts of molecular oxygen generated by enzyme-catalyzed decomposition of hydrogen peroxide.
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All authors Nicholas A. Nunn, Antonin Marek, Alex I. Smirnov, Olga A. Shenderova, Marco D. Torelli

Statistical Mechanics · Cross-listed from quant-ph

The bulk spectral gap is certifiable from above but uncomputable from below

Xiangling Xu, Matthias Schötz, Jie Wang et al. (+4 more)

Determining spectral gaps in the thermodynamic limit is a central challenge in quantum many-body physics. When a fixed boundary condition is imposed, this problem is undecidable: no algorithm, even with unlimited resources, can decide for every Hamiltonian whether it is gapped. Yet the thermodynamic limit is meant to capture the intrinsic properties of very large systems, which should not depend on how their boundaries are chosen. We therefore consider the bulk spectral gap, which concerns only the intrinsic excitations of the infinite system, and ask what can and cannot be computed about it. First, we give a general algorithm producing a hierarchy of certified upper bounds on the bulk gap, arbitrarily tight at the cost of more computation. Second, we prove that the spectral gap problem remains undecidable in the bulk, already for translationally invariant nearest-neighbour chains of fixed local dimension. Hence no general algorithm produces convergent lower bounds, and no convergent upper-bounding algorithm, ours included, admits a computable convergence rate. The bulk spectral gap is thus certifiable from above but uncomputable from below; more precisely, the bulk-gaplessness promise problem is RE-complete, exactly as hard as the halting problem. The same construction shows that no general algorithm can decide whether a given product state is a ground state, and that convergent bounds on ground-state expectation values admit no computable convergence rate in general. Finally, we obtain the first nontrivial certified upper bounds on the bulk gap of the spin-1/2 kagome Heisenberg antiferromagnet.
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All authors Xiangling Xu, Matthias Schötz, Jie Wang, Victor Magron, Igor Klep, Omar Fawzi, Marc-Olivier Renou

2606.03836 · 2 Jun · 48 pages, 5 figures, incl. SI (38 pages). Comments welcome! v5: improved kagome bounds; clearer presentation. v4: uncomputability of KMS ground states and their expectation values; instability under onsite perturbations. v3: uncomputability from below, RE-completeness, new title (previously: The bulk spectral gap is semi-decidable: a convergent family of certified upper bounds)

Abstract PDF $ALGO ×5$HAML ×1$QNTM ×1$SPIN ×1

Materials Science

Fracture energy of 6H-SiC at the microscale: effects of testing geometry and notch preparation

Zhuoqi Lucas Li, Siyang Wang, Ao Li et al. (+5 more)

Micromechanical testing enables small-scale fracture energy measurements, but values depend strongly on geometry and specimen preparation. Here, the fracture energy of the single-crystal 6H-SiC {10-10} plane was measured using microscale double cantilever beam (DCB) and single cantilever beam (SCB) geometries. DCBs showed stable crack growth under displacement control and obtained 7.5 +- 0.3 J/m2. In contrast, SCBs notched by a Ga focused ion beam gave fracture energies over twice this value, indicating Ga implantation and near-notch residual stresses. Increasing the final notching current increased the measured fracture energy further. Although near-cryogenic notching limited ion-beam-induced damage, it did not reconcile SCB-derived values with DCB test results. Vacuum annealing substantially lowered the fracture energy and brought SCB results into close agreement with DCB measurements, whereas annealing in argon was less effective. Our findings highlight the importance of careful sample preparation and testing geometry selection for reliable fracture property measurement in ceramic materials.
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All authors Zhuoqi Lucas Li, Siyang Wang, Ao Li, James O. Douglas, Florian Bouville, Oriol Gavalda-Diaz, Katharina Tinka Marquardt, Finn Giuliani

Materials Science

RamanGPT: Bidirectional Mapping Between Crystal Structures and Raman Spectra with Graph Neural Networks and Generative Transformers

Frank M. Abel, Jaehyung Lee, Charles R. Campbell et al. (+1 more)

Raman spectroscopy is one of the most accessible vibrational probes in materials laboratories, but its forward problem (structure to spectrum) is bottlenecked by the cost of density functional perturbation theory, and its inverse problem (spectrum to structure) typically relies on retrieval against curated references. We introduce RamanGPT, a deep-learning framework that addresses both directions for crystalline inorganic materials. The forward model, an Atomistic Line Graph Neural Network (ALIGNN), is trained on the 5{,}099-material Computational Raman Database and predicts 200-bin spectra over 50-1000~cm$^{-1}$ with 42.5% having a cosine similarity greater than or equal to 0.354 suggesting qualitative features of the target spectrum. The model also shows some qualitative agreement with the approximate features and appearance of similar relative intensity of the modes to an experimental measurement of metallic 1T VSe$_{2}$, a system absent from the training set. The inverse model fine-tunes a large language model via Quantized Low-Rank Adaptation on Raman-plus-formula prompts, recovering lattice parameters with mean absolute errors of 1.14-2.16~Å and reduced-formula consistency of 86.8% on 508 held-out materials. A cosine-similarity matcher and an inverse$\rightarrow$relax$\rightarrow$forward consistency loop are deployed at https://atomgpt.org/raman.
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All authors Frank M. Abel, Jaehyung Lee, Charles R. Campbell, Kamal Choudhary

Soft Condensed Matter

Continuous limit of a discrete stochastic model of cell migration

Nino Despeignes and Marc Durand

We analytically derive the continuous limit of the Cellular Potts Model (CPM) for a one-dimensional cell subjected to constant and run-and-tumble driving forces. By coarse-graining the discrete lattice dynamics, we obtain the Fokker-Planck equations governing the cell's size and center-of-mass position. We show that in the low-force regime, the cell dynamics are accurately described by an overdamped Langevin equation. Beyond this regime, we expose intrinsic algorithmic artifacts, including a force-dependent diffusion coefficient, a non-linear force-velocity relationship, and the breakdown of the Einstein relation. We demonstrate that replacing the conventional Metropolis update rule with Glauber dynamics significantly mitigates these artifacts, broadening the physically valid parameter space. Our exact results bridge the gap between lattice-based simulations and continuous active matter models.
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Materials Science

Demonstrating magnetic memory in iron-rhodium structures using a quantum diamond microscope

Kristine V. Ung, Gregory M. Stephen, Nicholas A. Blumenschein et al. (+7 more)

Iron-rhodium (FeRh) has a first-order phase transition near room temperature between antiferromagnetic (AFM) and ferromagnetic (FM) phases, making it a promising material for magnetic memory technologies like heat-assisted magnetic recording (HAMR). It has a comparatively sharper phase transition and lower writing temperature than alternative materials, implying less thermal engineering constraints and an increase in write/read head lifetime. Despite great effort, however, AFM-based magnetic memory using FeRh has not yet been realized. Here, we employ both wide-field and scanning nanoscale quantum diamond microscopes (QDMs) to image directly the magnetic field of a patterned FeRh thin film structure under ambient conditions, demonstrating a magnetic recording technique that is reliable and robust. We experimentally identify coupling between the Néel and magnetization vector directions; and also, that the magnetic orientation of the FM phase uniquely determines the Néel vector in the AFM phase, due to pinned uncompensated magnetic moments (UMMs) in the FeRh structure. Thus, the magnetic orientation is maintained when the system is cycled between AFM and FM phases, providing the foundation for a practical, AFM-based magnetic memory.
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All authors Kristine V. Ung, Gregory M. Stephen, Nicholas A. Blumenschein, Alexander J. Edwards, Samuel W. LaGasse, Steven P. Bennett, Aubrey T. Hanbicki, Ronald L. Walsworth, Adam L. Friedman, Paul V. Petruzzi

Strongly Correlated Electrons

Probing metal-insulator criticality with cavity photons

João C. Inácio, Natanael C. Costa and Fakher F. Assaad

The Hubbard model on the honeycomb lattice is a pristine realisation of a semimetal-to-insulator Mott transition belonging to the O(3) Gross-Neveu universality class. We couple this system to a single linearly polarised, uniform cavity photon mode. For this interacting light-matter model, we formulate a negative-sign-free fermion quantum Monte Carlo algorithm that allows for unbiased results on finite system sizes. Our numerical results show that the coupling to the cavity is irrelevant at criticality, even at strong electron-photon coupling. On the other hand, we observe, and show analytically, that the photon spectrum acquires finite corrections in the form of the optical conductivity. In the semimetal phase, gapless particle-hole excitations produce a low-energy polaritonic mode, which is suppressed in the Mott insulator phase. Furthermore, we show that the photon spectra can be used to detect universal information about the quantum critical point. Thereby, our results establish that a single, uniform cavity photon mode acts as a contact-free non-invasive probe for Mott criticality. Our results can be generalised to any cavity where an intensive number of uniform linearly polarised photon modes couple to the electronic system.
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Mesoscale and Nanoscale Physics

Mechanochemical Nano-Writing of an Atomically Thin Metal

Shuai Zhang, Yanyu Jia, Atanu Samanta et al. (+14 more)

Mechanical energy accelerates many physicochemical processes, including materials syntheses that are hard to produce with thermal energy alone. However, physical understanding connecting applied mechanical forces with internal stresses and ensuing reaction mechanisms is lacking. Here we demonstrate mechanical force-enabled synthesis and nanoscale patterning to metallize a two-dimensional (2D) material, producing an atomically-thin superconducting material. Localized force applied by atomic force microscope tips to van der Waals (vdW) encapsulated stacks of 2D bilayer MoTe2 and adjacent source Pd guides 2D Pd7MoTe2 growth with 50 nm lateral resolution. Force accelerates reaction kinetics exponentially per Eyring's stress-assisted thermal activation model, reducing synthesis temperatures from ~200 {\deg}C to near-room temperature. Finite element simulations, density functional theory, and ab-initio grand canonical Monte Carlo calculations show that tip-induced compression facilitates Pd chemisorption to tensile-strained MoTe2 that converts to uniform Pd7MoTe2. This demonstrates a new, generalizable paradigm for nanoscale synthesis of quantum materials, and high-precision engineering of superconductivity.
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All authors Shuai Zhang, Yanyu Jia, Atanu Samanta, Yutian Bao, Haosen Guan, Zhaoyi Joy Zheng, Guangming Cheng, Ting Liu, Cangyu Qu, Kenji Watanabe, Takashi Taniguchi, Nan Yao, Ashlie Martini, Leslie Schoop, Andrew M. Rappe, Sanfeng Wu, Robert W. Carpick