Quantum Gases
J. Marijan, H. Strobel, M. K. Oberthaler et al. (+1 more)
We investigate
entropy transport for universal scaling phenomena in closed
quantum many-body systems far from
equilibrium. From spatially resolved experimental data of a spinor Bose gas, we demonstrate that
entropy decreases on long-distance scales while it increases at short distances. A dynamical separation of scales leads to macrophysics with long-range order, which is insensitive to the highly entropic microphysical processes. Since the total von Neumann
entropy is conserved on a fundamental level for the
quantum system, our analysis reveals a reciprocal connection between the emergence of macroscopic structure and microscopic disorder. To illustrate the scope of this connection, we exemplify the universal phenomenon also in a relativistic
quantum field theory calculation from first principles, which is relevant for particle physics and early-universe cosmology.
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All authors J. Marijan, H. Strobel, M. K. Oberthaler, J. Berges
Other Condensed Matter · Cross-listed from hep-th
Revisiting Schrödinger CFTs: Factorization, Massless Particles, and a Path to the Bootstrap
Mathieu Boisvert, Shehab Hossam Fadda, Justin Kulp et al. (+1 more)
We revisit Schrödinger CFTs from a modern point of view. We introduce the ”harmonic trap geometry,” analogous to the cylinder picture in relativistic CFTs, and demonstrate a state-operator correspondence that applies to all operators, including descendant, massless, and ”normal-ordered operators.” A thermofield double construction plays an extremely important role. We systematically classify all physical spectra in the harmonic trap and their unitarity bounds, extending earlier results to include both massless and massive states of all
spins, providing a new analytic treatment of unitarity bounds, and establishing foundations for a bootstrap. In our reformulation, previously known perturbative non-renormalization
theorems follow immediately from non-perturbative factorization at fixed points and along RG flows. Massless states are described by an effective 1d CFT, as predicted by DLCQ, and violate the non-renormalization
theorems. We include a self-consistent review of Schrödinger CFTs in our framework, making the paper accessible to anyone with a field theory background.
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All authors Mathieu Boisvert, Shehab Hossam Fadda, Justin Kulp, Ramtin M. Yazdi
Strongly Correlated Electrons
Interpretable Artificial Intelligence (AI) Analysis of Strongly Correlated Electrons
Changkai Zhang and Jan von Delft
Artificial Intelligence (AI) has become an exceptionally powerful tool for analyzing scientific data. In particular,
attention-based architectures have demonstrated a remarkable capability to capture complex correlations and to furnish interpretable insights into latent, otherwise inconspicuous patterns. This progress motivates the application of AI techniques to the analysis of strongly correlated electrons, which remain notoriously challenging to study using conventional theoretical approaches. Here, we propose novel AI workflows for analyzing snapshot
datasets from tensor-network simulations of the two-dimensional (2D) Hubbard model over a broad range of temperature and doping. The 2D Hubbard model is an archetypal strongly correlated system, hosting diverse intriguing phenomena including Mott
insulators, anomalous metals, and high-$T_c$ superconductivity. Our AI techniques yield fresh perspectives on the intricate
quantum correlations underpinning these phenomena and facilitate universal omnimetry for ultracold-atom simulations of the corresponding strongly correlated systems.
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Mesoscale and Nanoscale Physics
Distributing entanglement between distant semiconductor qubit registers using a shared-control shuttling link
Zarije Ademi, Marion Bassi, Cécile X. Yu et al. (+8 more)
Semiconductor quantum processors have potential to scale to modular
quantum computers, in which
qubit registers are coupled by
quantum links, enabling high connectivity and space for control circuitry. Individual
spin-
qubit registers have progressed to two-dimensional systems and execution of small
quantum algorithms. Separately, high-fidelity
spin shuttling has been demonstrated in linear channels defined by individual gate electrodes. Here, we realize the first shared-control shuttling link integrated between distant
qubit registers to demonstrate
quantum entanglement in a basic modular
quantum processor based on hole
spin qubits in germanium. We develop a protocol to compensate for
spin-orbit-induced rotations during
qubit transfer, allowing for shuttling between
qubit registers separated by more than one micrometer in approximately a hundred nanoseconds. Combining local
qubit operation with coherent shuttling, we generate Bell states formed by
spins residing in separate registers. Characterizing them using
quantum state
tomography, we demonstrate
entanglement between
spin qubits in distant registers.
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All authors Zarije Ademi, Marion Bassi, Cécile X. Yu, Stefan D. Oosterhout, Yuta Matsumoto, Sander L. de Snoo, Amir Sammak, Lieven M. K. Vandersypen, Giordano Scappucci, Corentin Déprez, Menno Veldhorst
Materials Science · Cross-listed from quant-ph
Programmable digital quantum simulation of 2D Fermi-Hubbard dynamics using 72 superconducting qubits
Faisal Alam, Jan Lukas Bosse, Ieva Čepaitė et al. (+41 more)
Simulating the time-dynamics of
quantum many-body systems was the original use of
quantum computers proposed by Feynman, motivated by the critical role of
quantum interactions between electrons in the properties of materials and molecules. Accurately simulating such systems remains one of the most promising applications of general-purpose digital
quantum computers, in which all the parameters of the model can be programmed and any desired physical quantity output. However, performing such simulations on today's
quantum computers at a scale beyond the reach of classical methods requires advances in the efficiency of simulation
algorithms and error mitigation techniques. Here we demonstrate programmable digital
quantum simulation of the dynamics of the 2D
Fermi-Hubbard model – one of the best-known simplified models of electrons in crystalline solids – at a scale beyond exact classical state-vector simulation. We implement simulations of this model on
lattice sizes up to ${6\times 6}$ using 72
qubits on Google's Willow
quantum processor, across a range of physical parameters, including different on-site electron-electron interaction strengths and
magnetic flux values, and study phenomena including formation of
magnetic polarons (charge carriers surrounded by local
magnetic polarisation), dynamical
symmetry-breaking in stripe-ordered states, attraction of charge carriers on an entangled background state known as a valence bond solid, and the approach to
equilibrium through thermalisation. We validate our results against exact calculations in parameter regimes where these are feasible, and compare them to approximate classical simulations performed using tensor network and operator propagation methods. Our results demonstrate that meaningful programmable digital
quantum simulation of many-body interacting electron models is now feasible on state-of-the-art
quantum hardware.
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All authors Faisal Alam, Jan Lukas Bosse, Ieva Čepaitė, Adrian Chapman, Laura Clinton, Marcos Crichigno, Elizabeth Crosson, Toby Cubitt, Charles Derby, Oliver Dowinton, Paul K. Faehrmann, Steve Flammia, Brian Flynn, Filippo Maria Gambetta, Raúl García-Patrón, Max Hunter-Gordon, Glenn Jones, Abhishek Khedkar, Joel Klassen, Michael Kreshchuk, Edward Harry McMullan, Lana Mineh, Ashley Montanaro, Caterina Mora, John J. L. Morton, Dhrumil Patel, Pete Rolph, Raul A. Santos, James R. Seddon, Evan Sheridan, Wilfrid Somogyi, Marika Svensson, Niam Vaishnav, Sabrina Yue Wang, Gethin Wright, Dmitry Abanin, Mohammed Alghadeer, Jaehong Choi, Tyler Cochran, Gaurav Gyawali, Shashwat Kumar, Ricky Oliver, Eliott Rosenberg, Pedram Roushan
Strongly Correlated Electrons
Jing-Yu Zhao and Ya-Hui Zhang
Understanding the mechanism of superconductivity in twisted
bilayer graphene (TBG) is a central challenge in correlated moiré materials. The most intriguing question is about the nature of the normal state: is the Cooper pair formed from small
Fermi surface or large
Fermi surface? Here, we propose a unified theoretical framework describing a symmetric pseudogap metal with small hole pockets, dubbed the second
Fermi liquid (sFL), which is topologically distinct from the conventional
Fermi liquid. Our theory shows that superconductivity in TBG emerges from the sFL phase, with local moment pairing transferred to mobile carriers, giving rise to a smaller nodal superconducting gap on the small hole pockets. This framework simultaneously explains the pseudogap metal above the transition temperature and the two-gap nematic superconductivity below it, providing a comprehensive understanding of correlated physics in TBG.
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Strongly Correlated Electrons
Spin Polarons in Flat Band Ferromagnets
Saranesh Prembabu, Rahul Sahay, Stefan Divic et al. (+1 more)
Spin polarons are bound states of electrons and
spin-flips that form above
spin polarized electronic
insulators.These bound states conventionally form in one of two settings: in frustrated
lattices with dispersive bands – where the motion of an electron preferences binding a nearby
spin-flip – or in topological flat bands – where the Chern number enforces an effective dipolar interaction between electrons and
spin flips. In this work, we report the formation of a
spin polaron in a context that doesn't fall cleanly into either of these paradigms. In particular, we study the one-dimensional Mielke-Tasaki chain, a paradigmatic model of flat band ferromagnetism, which has an exact
ferromagnetic ground state, trivial band
topology, and quenched kinetic energy in its lowest band. Despite these features, our density
matrix renormalization group simulations reveal the presence of
spin polarons upon electron doping this model. More surprisingly, combining these numerics with analytic calculations, we show that polaron binding occurs when the interaction-induced kinetic energy of the model is zero – contrary to intuition from kinetic magnetism – and the glue binding the electrons and
spin-flips arises from weak mixing with the model's dispersive band – contrary to what occurs in topological flat bands. Our results open the doors to exploring how the
quantum geometry of flat bands drives the formation of exotic charge carriers.
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All authors Saranesh Prembabu, Rahul Sahay, Stefan Divic, Ashvin Vishwanath
Disordered Systems and Neural Networks · Cross-listed from cs.LG
Learning Pseudorandom Numbers with Transformers: Permuted Congruential Generators, Curricula, and Interpretability
Tao Tao and Maissam Barkeshli
We study the ability of
Transformer models to learn sequences generated by Permuted Congruential Generators (PCGs), a widely used family of pseudo-random number generators (PRNGs). PCGs introduce substantial additional difficulty over linear congruential generators (LCGs) by applying a series of bit-wise shifts, XORs, rotations and truncations to the hidden state. We show that
Transformers can nevertheless successfully perform in-context prediction on unseen sequences from diverse PCG variants, in tasks that are beyond published classical attacks. In our experiments we scale
moduli up to $2^{22}$ using up to $50$ million model parameters and
datasets with up to $5$ billion
tokens. Surprisingly, we find even when the output is truncated to a single bit, it can be reliably predicted by the model. When multiple distinct PRNGs are presented together during training, the model can jointly learn them, identifying structures from different permutations. We demonstrate a scaling law with modulus $m$: the number of in-context sequence elements required for near-perfect prediction grows as $\sqrt{m}$. For larger
moduli, optimization enters extended stagnation phases; in our experiments, learning
moduli $m \geq 2^{20}$ requires incorporating training data from smaller
moduli, demonstrating a critical necessity for curriculum learning. Finally, we analyze
embedding layers and uncover a novel clustering phenomenon: the top principal components spontaneously group the integer inputs into bitwise rotationally-invariant clusters, revealing how representations can transfer from smaller to larger
moduli.
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Strongly Correlated Electrons · Cross-listed from hep-th
Perfect Particle Transmission through Duality Defects
Atsushi Ueda, Vic Vander Linden, Laurens Lootens et al. (+3 more)
We study wavepackets that propagate across (a) topological interfaces in
quantum spin systems exhibiting non-invertible
symmetries and (b) duality defects coupling dual theories. We demonstrate that the transmission is always perfect, and that a particle traversing the interface is converted into a nonlocal string-like excitation. We give a systematic way of constructing such a defect by identifying its
Hilbert space with the virtual bond dimension of the
matrix product operator representing defect lines. Our work both gives an operational meaning to topological interfaces, and provides a
lattice analogue of recent results solving the monopole paradox in
quantum field theory.
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All authors Atsushi Ueda, Vic Vander Linden, Laurens Lootens, Jutho Haegeman, Paul Fendley, Frank Verstraete
Strongly Correlated Electrons
Role of Phase Fluctuation in Dynamic Competition Between Charge Order and Superconductivity in Cuprates
Mingu Kang, Pavel E. Dolgirev, Chao C. Zhang et al. (+9 more)
Phase fluctuations are a key factor distinguishing nonthermal (ultrafast) and thermal phase transitions. Charge order in cuprates is characterized by short-range coherence while competing with superconductivity, and as such, it provides a representative case to study the role of phase fluctuation in coupled order parameter dynamics. In this work, we investigated the intertwined
evolution of charge order and superconductivity in cuprate/manganite
heterostructures using time-resolved resonant X-ray scattering. The resulting dynamics are analyzed within a space- and time-dependent nonperturbative model capturing both amplitude and phase dynamics. At low fluence, photo-induced suppression of superconductivity results in a nonthermal enhancement of charge order, underscoring the dynamic competition between charge order and superconductivity. With increasing fluence, the slowing down of melting and recovery dynamics is observed, indicating a critical role of phase fluctuations. At high fluence, both charge order and superconductivity remain suppressed for an extended time window due to decoupling between amplitude and phase dynamics and the delayed recovery of phase coherence. Our work underscores the importance of phase fluctuation for understanding the dynamic competition between order parameters in cuprates.
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All authors Mingu Kang, Pavel E. Dolgirev, Chao C. Zhang, Hoyoung Jang, Byungjune Lee, Minseok Kim, Sang-Youn Park, Ronny Sutarto, Eugene Demler, Jae-Hoon Park, John Y. T. Wei, Riccardo Comin
Statistical Mechanics · Cross-listed from quant-ph
Approximate quantum error correction, eigenstate thermalization and the chaos bound
Shozab Qasim and Jason Pollack
Quantum error correction, thermalization, and
quantum chaos are fundamental aspects of
quantum many-body physics that have each developed largely independently, despite their deep conceptual overlap. In this work, we establish a precise link between all three in systems that satisfy the eigenstate thermalization hypothesis (ETH) and exhibit a well-defined hierarchy of time scales between dissipation and scrambling. Building on the ETH
matrix ansatz and the structure of the out-of-time-order correlator (OTOC), we show that the chaos bound directly constrains the error of an approximate
quantum error-correcting code. This establishes a quantitative relation between information scrambling, thermalization, and correctability. Furthermore, we derive bounds on dynamical fluctuations around the infinite-time average and on fluctuation-dissipation relations, expressed in terms of both the code error and the Lyapunov exponent. Our results reveal how the limits of
quantum chaos constrain information preservation in thermalizing
quantum systems.
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Quantum Gases
Single-fluid model for rotating annular supersolids and its experimental implications
Niccolò Preti, Nicolò Antolini, Charles Drevon et al. (+6 more)
The famous two-fluid model of finite-temperature superfluids has been recently extended to describe the mixed classical-superfluid dynamics of the newly discovered supersolid phase of matter. We show that for rigidly rotating supersolids one can derive a more appropriate single-fluid model, in which the seemingly classical and superfluid contributions to the motion emerge from a spatially varying phase of the global wavefunction. That allows to design experimental protocols to excite and detect the peculiar rotation dynamics of annular supersolids, including partially quantized supercurrents, in which each atom brings less than $\hbar$ unit of angular momentum. Our results are valid for a more general class of density-modulated superfluids.
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All authors Niccolò Preti, Nicolò Antolini, Charles Drevon, Pietro Lombardi, Andrea Fioretti, Carlo Gabbanini, Giovanni Ferioli, Giovanni Modugno, Giulio Biagioni
Quantum Gases · Cross-listed from physics.atom-ph
Wavefront Curvature and Transverse Atomic Motion in Time-Resolved Atom Interferometry: Impact and Mitigation
Noam Mouelle, Jeremiah Mitchell, Valerie Gibson et al. (+1 more)
Time-resolved atom interferometry, as employed in applications such as gravitational wave detection and searches for ultra-light dark matter, requires precise control over systematic effects. In this work, we investigate phase noise arising from shot-to-shot fluctuations in the atoms' transverse motion in the presence of the wavefront
curvature of the interferometer beam, and analyse its dependence on the
laser-beam geometry in long-baseline, large-momentum-transfer atom interferometers. We use a semi-classical framework to derive analytical expressions for the effective phase perturbation in position-averaged measurements and validate them using Monte Carlo simulations. Applied to 100-m and 1-km atom gradiometers representative of next-generation experiments, the model shows that configurations maximizing pulse efficiency also amplify
curvature-induced phase noise, requiring micron-level control of the atom cloud's centre-of-mass position and sub-micron-per-second control of its centre-of-mass velocity to achieve sub-$10^{-5}$ rad phase stability. Alternative beam geometries can suppress this noise by up to two orders of magnitude, but at the cost of reduced pulse efficiency. To address this limitation, we propose a mitigation strategy based on position-resolved phase-shift readout, which empirically learns and corrects the wavefront-induced bias from measurable quantities such as the phase-shift gradient and final cloud position. This approach restores high-sensitivity operation in the maximum-pulse-efficiency configuration without detailed beam characterisation, providing a practical route towards next-generation, time-resolved atom interferometers operating at the $10^{-5}$ rad noise level.
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All authors Noam Mouelle, Jeremiah Mitchell, Valerie Gibson, Ulrich Schneider
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Digitized Counterdiabatic Quantum Sampling
Narendra N. Hegade, Nachiket L. Kortikar, Balaganchi A. Bhargava et al. (+9 more)
We propose digitized counterdiabatic
quantum sampling (DCQS), a hybrid
quantum-classical
algorithm for efficient sampling from energy-based models, such as low-temperature Boltzmann distributions. The method utilizes counterdiabatic protocols, which suppress non-adiabatic transitions, with an iterative bias-field procedure that progressively steers the sampling toward low-energy regions. We observe that the samples obtained at each iteration correspond to approximate Boltzmann distributions at effective temperatures. By aggregating these samples and applying classical reweighting, the method reconstructs the Boltzmann distribution at a desired temperature. We define a scalable performance metric, based on the Kullback-Leibler divergence and the total variation distance, to quantify convergence toward the exact Boltzmann distribution. DCQS is validated on one-dimensional Ising models with random couplings up to 124
qubits, where exact results are available through transfer-
matrix methods. We then apply it to a higher-order
spin-glass
Hamiltonian with 156
qubits executed on IBM
quantum processors. We show that classical sampling
algorithms, including Metropolis-Hastings and the state-of-the-art low-temperature technique parallel tempering, require up to three orders of magnitude more samples to match the quality of DCQS, corresponding to an approximately 2x runtime advantage. Boltzmann sampling underlies applications ranging from statistical physics to machine learning, yet classical
algorithms exhibit exponentially slow convergence at low temperatures. Our results thus demonstrate a robust route toward scalable and efficient Boltzmann sampling on current
quantum processors.
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All authors Narendra N. Hegade, Nachiket L. Kortikar, Balaganchi A. Bhargava, Juan F. R. Hernández, Alejandro Gomez Cadavid, Pranav Chandarana, Sebastián V. Romero, Shubham Kumar, Anton Simen, Anne-Maria Visuri, Enrique Solano, Paolo A. Erdman
Mesoscale and Nanoscale Physics
Impact of hydrogenation on the structure, chemistry, and electrical properties of flame-synthesized carbon nanoparticle films
Luca Basta, Francesca Picca, Pegah Darvehi et al. (+8 more)
The interaction between hydrogen atoms and carbon nanoparticles is a fundamental process governing the properties of carbonaceous materials in environments ranging from combustion systems to the interstellar medium. This study investigates the effects of controlled atomic hydrogen exposure on young and mature soot nanoparticles, generated in premixed ethylene-air flames, and deposited on substrates. We employed a multi-technique approach to characterize the chemical, mechanical, and electrical
evolution of the films. In-situ infrared spectroscopy revealed non-monotonic behavior: an initial increase in aliphatic CH bonds was observed, followed by a decrease at higher hydrogen fluences. This was accompanied by a continuous decrease in the aromatic C=C signal. Atomic force microscopy showed a significant increase in the Young's modulus of the film for both sample types after hydrogenation. This mechanical change was correlated with an increase in the I(D)/I(G) ratio from Raman spectroscopy. Furthermore, both macroscopic current vs. voltage and local scanning tunneling spectroscopy measurements demonstrated a notable increase in electrical conductivity. For single just-formed soot particles, moreover, a hydrogen-induced transformation from a semiconductive to a semi-metallic nature was observed. The collective evidence points towards an H-induced CC cross-linking mechanism within the nanoparticle films. We propose that atomic hydrogen facilitates the formation of radical sites, which promotes covalent bond formation between adjacent particles or molecular units, creating a more interconnected and rigid network, with smaller interlayer distance. These findings provide crucial insights into the structural
evolution of carbonaceous materials in hydrogen-rich environments, with direct implications for understanding soot formation and for the tailored design of carbon-based materials.
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All authors Luca Basta, Francesca Picca, Pegah Darvehi, Vincenzo Pagliara, Alberto Aloisio, Mario Commodo, Patrizia Minutolo, Vito Mennella, Stefan Heun, Stefano Veronesi, Andrea D'Anna
Superconductivity
Emergence of charge-$4e$ superconductivity from 2D nematic superconductors
Xuan Zou, Zhou-Quan Wan and Hong Yao
Charge-$4e$ superconductivity is an exotic state of matter that may emerge as a vestigial order from a charge-$2e$
superconductor with multicomponent superconducting order parameters. Showing its emergence in a
lattice phase model from numerically exact large-scale computations has remained rare. Here, we propose a kagome
lattice model with a nematic superconducting ground state and show that it supports a rich set of vestigial phases at elevated temperatures, including a charge-$4e$ phase and a quasi-long-range nematic phase, through large-scale Monte Carlo simulations. Combining theoretical analysis with Monte Carlo simulations, we uncover the nature of these phases and show that the phase transitions are governed by the proliferation of distinct topological defects: the $(\tfrac{1}{2},0)$ half superconducting
vortices, the $(\tfrac{1}{2},\tfrac{1}{2})$
vortices, the $(0,1)$ integer nematic
vortices, and domain-wall excitations. In particular, we demonstrate that domain-wall proliferation is crucial for the quasi-nematic phase and should be carefully accounted for when analyzing phase transitions associated with vestigial charge-$4e$ order.
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Strongly Correlated Electrons
Probing Topological Phases in a Strongly Correlated Ladder Model via Entanglement
Aminul Hussain, Nisa Ara, Rudranil Basu et al. (+1 more)
The interplay between non-trivial band
topology and strong electronic correlations is a central challenge in modern condensed matter physics. We investigate this competition on a two-leg ladder model with a p-wave-like hybridisation between the legs. This model hosts a
symmetry-protected topological phase in its non-interacting limit. Using the density-
matrix renormalisation group
algorithm, we compute the comprehensive
quantum phase diagram in the presence of a repulsive inter-leg density-density interaction. Our analysis, based on
entanglement entropy and the
entanglement spectrum, reveals a fascinating dichotomy in the stability of the topological phase. We find a non-trivial change in the value of the edge
entanglement entropy as we include interaction. Furthermore, we find that the phase boundary separating a trivial
insulator phase and a topological one with winding number two remains robustly pinned at its non-interacting location, irrespective of the interaction strength. Variation of the effective conformal field theory's central charge near the critical line explains the robustness of the gap. In contrast, the transition to an insulating phase with winding number one is heavily renormalised, with the critical line shifting significantly as the interaction increases. By successfully mapping the phase diagram and identifying the distinct behaviours of the phase boundaries, our work clarifies how interactions can selectively preserve or destroy different aspects of a topological phase.
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All authors Aminul Hussain, Nisa Ara, Rudranil Basu, Sudeshna Sen
Statistical Mechanics · Cross-listed from quant-ph
Witnessing Short- and Long-Range Nonstabilizerness via the Information Lattice
Yuliya Bilinskaya, Miguel F. Martínez, Soumi Ghosh et al. (+3 more)
We study nonstabilizerness on the information
lattice and demonstrate that noninteger local information directly indicates nonstabilizerness. For states with a clear separation of short- and large-scale information, a noninteger total information at large scales $\Gamma$ serves as a witness of long-range nonstabilizerness. We propose a folding procedure to separate the global and edge-to-edge contributions to $\Gamma$. As an example we show that the
ferromagnetic ground state of the
spin-1/2 three-state Potts model has long-range nonstabilizerness originating from global correlations, while the paramagnetic ground state has at most short-range nonstabilizerness.
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All authors Yuliya Bilinskaya, Miguel F. Martínez, Soumi Ghosh, Thomas Klein Kvorning, Claudia Artiaco, Jens H. Bardarson
Materials Science
Temperature dependent ferroelectricity in strained KTaO3 with machine learned force field
Yu Zhu, Luigi Ranalli, Taikang Chen et al. (+2 more)
Ferroelectric materials are a class of dielectrics that exhibit spontaneous polarization which can be reversed under an external electric field. The emergence of ferroelectric order in incipient ferroelectrics is a topic of considerable interest from both fundamental and applied perspectives. Among the various strategies explored, strain engineering has been proven to be a powerful method for tuning ferroelectric polarization in materials. In the case of KTaO3, first principles calculations have suggested that strain can drive a ferroelectric phase transition. In this study, we investigate the impact of in-plane uniaxial and biaxial strain, ranging from 0% to 1%, on pristine KTaO3 to explore its potential for ferroelectricity induction via inversion
symmetry breaking. By integrating density functional theory calculations with the
stochastic self-consistent harmonic approximation assisted by on the fly machine learned force field, we obtain accurate structural information and dynamical properties under varying strain conditions while incorporating higher-order anharmonic effects. Employing the Berry phase method, we obtained the ferroelectric polarization of the strained structures over the entire temperature range up to 300 K. Our findings provide valuable insights into the role of strain in stabilizing ferroelectricity in KTaO3, offering guidance for future experimental and theoretical studies on strain-engineered ferroelectric materials.
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All authors Yu Zhu, Luigi Ranalli, Taikang Chen, Wei Ren, Cesare Franchini
Strongly Correlated Electrons
Steffen Bollmann, Andreas Haller, Jukka I. Väyrynen et al. (+2 more)
Motivated by recent observations of fractional Chern
insulators (FCIs) in the vicinity of superconducting (SC) phases, we study fractional
quantum (anomalous)
Hall-
superconductor heterostructures in the presence of $U(1)$ order-parameter fluctuations and particularly focus on the case of $\nu = 2/3$
quantum Hall states leading to $\mathbb Z_3$ parafermions. We first employ a phenomenological field theory to qualitatively determine the phase diagram. Furthermore, we generalize a previously established alternating pattern of
superconductor and tunneling regions, coupled to fractional
quantum Hall edge states, to map the problem onto a topological Josephson junction chain involving
lattice parafermions. Using density
matrix renormalization group simulations, we establish a phase diagram composed of Mott insulating phases and two different Luttinger
liquids whose fundamental excitations carry charges 2e and $2e/3$, respectively. In agreement with analytical considerations using conformal field theory, we numerically find transitions of Berezinskii-Kosterlitz-Thouless (BKT) type as well as a continuous $\mathbb Z_3 \times U(1)$ second-order phase transition characterized by central charge c = 9/5. We finally extract information about a possible ground state degeneracy and comment on the stability of parafermionic edge states in the presence of fluctuations. These theoretical foundations can be expected to be of practical importance for gate-defined FCI-SC
heterostructures in moiré materials, in which broad superconducting transitions indicative of strong order parameter fluctuations were observed.
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All authors Steffen Bollmann, Andreas Haller, Jukka I. Väyrynen, Thomas L. Schmidt, Elio J. König
Strongly Correlated Electrons
Fractional Chern insulators on cylinders: Tao-Thouless states and beyond
Felix A. Palm, Chloé Van Bastelaere and Laurens Vanderstraeten
Topological phases in two-dimensional
quantum lattice models are often studied on cylinders for revealing different topological properties and making the problem numerically tractable. This makes a proper understanding of finite-circumference effects crucial for reliably extrapolating the results to the thermodynamic limit. Using
matrix product states, we investigate these effects for the Laughlin-1/2 phase in the Hofstadter-Bose-Hubbard model, which can be viewed as the
lattice discretization of the bosonic
quantum Hall problem in the continuum. We propose a scaling of the model's parameters with the cylinder circumference that simultaneously approaches the continuum and thermodynamic limits. We find that different scaling schemes yield distinct topological signatures: we either retrieve a spontaneous formation of charge density wave ordering reminiscent of the Tao-Thouless states, known from the continuum problem on thin cylinders, or we find uniform states with a topological degeneracy that can be identified as minimally entangled states known from studies of
chiral spin liquids on cylinders. Finally, we carry out a similar analysis of the non-Abelian Moore-Read phase in the same model. Our results clarify the role of
symmetries in numerical studies of topologically ordered states on cylinders and highlight the role of
lattice effects.
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Mesoscale and Nanoscale Physics
Giant orbital Zeeman effects in a magnetic topological van der Waals interphase
Tobias Wichmann, Mirco Sastges, Keda Jin et al. (+10 more)
Van der Waals (vdW)
heterostructures allow the engineering of
magnetic and electronic properties via interfacial orbital hybridisation and charge transfer. The resulting electric fields can give rise to Rashba
spin-orbit coupling and Dzyaloshinskii-Moriya interactions, which may stabilise novel two-dimensional
magnetic phases. While such emergent
magnetic 'interphases' may offer a promising platform for
spin-based electronics, direct spectroscopic evidence for them is still lacking. Here, we report electric-field tunable Zeeman effects with Landé $g$-factors up to $\approx230$ at the interface of
graphene and the vdW ferromagnet Fe$_3$GeTe$_2$. They arise from an interplay of local-moment canting and the itinerant orbital moments of Fe$_3$GeTe$_2$, producing a
giant asymmetric level splitting. Exploiting the inelastic
phonon gap of
graphene, scanning tunnelling spectroscopy allows us to access the buried interface properties, and quantify Faraday-like screening. Our findings provide new insights and opportunities for electrically controlled interface magnetism, e.g. for spintronics and orbitronics devices.
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All authors Tobias Wichmann, Mirco Sastges, Keda Jin, Jose Martinez-Castro, Tom G. Saunderson, Dongwook Go, Honey Boban, Samir Lounis, Lukasz Plucinski, Markus Ternes, Yuriy Mokrousov, F. Stefan Tautz, Felix Lüpke
Soft Condensed Matter
Enzyme Active Bath Affects Protein Condensation
Kevin Ching, Anthony Estrada, Nicholas M Rubayiza et al. (+3 more)
We investigate how an active bath of enzymes influences the
liquid-
liquid phase separation (LLPS) of a non-interacting condensing
protein. The enzyme we choose to use as the active driver is urease, an enzyme that has been shown by several groups to exhibit enhanced
diffusion in the presence of its substrate. The non-interacting LLPS
protein is ubiquilin-2, a
protein that condenses with increasing temperature and salt. Using a microfluidic device with semipermeable membranes, we create a chemostatic environment to maintain the substrate content to feed the enzymatic bath and remove the products of the chemical reaction. Thus, we isolate the physical enhanced fluctuations from the chemical changes of the enzyme activity. We also compare the results to controls without activity or in the presence of the products of the reaction. We find that the active bath is able to enhance droplet size, density, and concentration, implying that more ubiquilin-2 is in condensed form. This result is consistent with an interpretation that the active bath acts as an effective temperature. Simulations provide an underlying interpretation for our experimental results. Together, these findings provide the first demonstration that physical enzymatic activity can act as an effective temperature to modify LLPS behavior, with implications for intracellular organization in the enzymatically active cellular environment.
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All authors Kevin Ching, Anthony Estrada, Nicholas M Rubayiza, Ligesh Theeyancheri, Jennifer M. Schwarz, Jennifer L Ross
Statistical Mechanics
Stochastic Resetting vs. Thermal Equilibration: Faster Relaxation, Different Destination
Nir Sherf, Remi Goerlich, Barak Hirshberg et al. (+1 more)
Stochastic resetting is known for its ability to accelerate search processes and induce non-
equilibrium steady states. Here, we compare the relaxation times and resulting steady states of resetting and thermal relaxation for Brownian motion in a harmonic potential. We show that resetting always converges faster than thermal equilibration, but to a different steady-state. The acceleration and the shape of the steady-state are governed by a single dimensionless parameter that depends on the resetting rate, the viscosity, and the stiffness of the potential. We observe a trade-off between relaxation speed and the extent of spatial exploration as a function of this dimensionless parameter. Moreover, resetting relaxes faster even when resetting to positions arbitrarily far from the potential minimum.
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All authors Nir Sherf, Remi Goerlich, Barak Hirshberg, Yael Roichman
Materials Science
Stabilization of Metallic, Excitonic Insulator, and Superionic Phases in Helium-Rare Gas Compounds at Sub-Terapascal Pressures
Cong Liu, Jordi Boronat and Claudio Cazorla
Helium and rare gases (RG: Ne, Ar, Kr, Xe) are typically considered chemically inert, yet under the extreme pressures of planetary interiors they may form compounds with unexpected properties. Using
crystal structure prediction and first-principles calculations, we mapped the phase diagram of binary He-RG systems up to $1$ TPa. We identify several previously unknown stoichiometric compounds that are both thermodynamically and vibrationally stable at sub-terapascal pressures, within the reach of modern high-pressure experiments. In particular, AHe$_{2}$ and AHe (A: Ar, Kr, Xe) adopt previously unreported orthorhombic, hexagonal and cubic phases that remain stable over wide pressure ranges. We further find that He-Xe systems host metallic and excitonic
insulator phases at pressures nearly an order of magnitude lower than those required for pure helium, offering a pathway to realize these exotic
quantum states experimentally. Finite-temperature simulations also reveal superionic He-Xe phases, in which helium ions diffuse either anisotropically or isotropically depending on the host
lattice. These findings constitute the first prediction of helium-based systems that combine
metallicity and superionicity, with profound implications for energy transport and planetary dynamo processes. Overall, our results demonstrate that mixing helium with heavier rare gases provides an effective strategy to stabilize metallic, excitonic
insulator, and superionic phases at experimentally accessible pressures, opening new research directions for condensed matter physics and planetary science.
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Materials Science · Cross-listed from physics.app-ph
Tailored heat treatments to characterise the fracture resistance of critical weld regions in hydrogen transmission pipelines
D.R. Chalfoun, J. Parker, M. Gagliano et al. (+1 more)
A new protocol is presented to directly characterise the toughness of microstructural regions present within the weld heat-affected zone (HAZ), the most vulnerable location governing the structural integrity of hydrogen transport pipelines. Heat treatments are tailored to obtain bulk specimens that replicate predominantly ferritic-bainitic, bainitic, and martensitic microstructures present in the HAZ. These are applied to a range of pipeline steels to investigate the role of manufacturing era (vintage versus modern), chemical composition, and grade. The heat treatments successfully reproduce the hardness levels and microstructures observed in the HAZ of existing natural gas pipelines. Subsequently, fracture experiments are conducted in air and pure H2 at 100 bar, revealing a reduced fracture resistance and higher hydrogen embrittlement susceptibility of the HAZ microstructures, with initiation toughness values as low as 32 MPa$\sqrt{\text{m}}$. The findings emphasise the need to adequately consider the influence of microstructure and hard, brittle zones within the HAZ.
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All authors D.R. Chalfoun, J. Parker, M. Gagliano, E. Martínez-Pañeda
Materials Science · Cross-listed from quant-ph
Diamond quantum sensing at record high pressure up to 240 GPa
Qingtao Hao, Ze-Xu He, Na Zuo et al. (+10 more)
Quantum sensing utilizing nitrogen-vacancy (NV) centers in diamond has emerged as a transformative technology for probing
magnetic phase transition1-4, evidencing Meissner effect of
superconductors1,5-9, and visualizing stress distribution3,9 under extreme conditions. Recent development in NV configurations and hydrostatic environments have raised the operational pressures of NV centers to 140 GPa2,6,10,11, but substantial challenges remain in extending sensing capabilities into multi-megabar range, critical for research in hydrogen-rich
superconductors like La-Sc-H ($T_{\text{c}}$ of 271-298 K at 195-266 GPa)12 and
evolution of minerals near Earth's core13. Here we report the fabrication of shallow NV centers through ion implantation followed by high-pressure and high-temperature (HPHT) annealing, leading to increased density, improved coherence, and mitigated internal stresses, a pre-requisite for reducing their degradation under compression. This NV magnetometry enable breakthrough of pressure capabilities exceeding 240 GPa, constrained by structural integrity of the 50 um diamond anvils, suggesting that the untapped pressure limit may enable further advancements with smaller cutlets or more robust diamonds. We present compelling evidence of the Meissner effect and trapped flux at record-high pressure of 180 GPa for superconducting transition in elemental titanium (Ti) as
benchmark, establishing a solid foundation for high-pressure magnetometry in exploring complex
quantum phenomena at previously unreachable pressures.
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All authors Qingtao Hao, Ze-Xu He, Na Zuo, Yang Chen, Xiangzhuo Xing, Xiaoran Zhang, Xinyu Zhuang, Zhixiang Shi, Xin Chen, Jian-Gang Guo, Gang-Qin Liu, Xiaobing Liu, Yanming Ma
Mesoscale and Nanoscale Physics
Experimental Milestones Towards Majorana Braiding with Acoustic Metamaterials
Jackson Saunders, Emil Prodan and Camelia Prodan
Here we show the first experimental implementation of the fully general Kitaev chain with complex-valued order parameter $\Delta$ and site-varying synthetic chemical potential $\mu$, using a passive multilayer acoustic resonator design and fabrication. Our laboratory model faithfully reproduces the key
symmetries and the topological phase diagram of the model, and displays robust Majorana-like edge modes spatially localized at smoothly engineered domain walls and energetically localized in the middle of the bulk spectral gap. We demonstrate precise control over mode positioning through smooth spatial variations of $\mu$, and validate the stability of the modes and of the spectral gap under continuous and complex variations of $\Delta$ – both critical requirements for topological braiding operations. These results establish and validate the fundamental building blocks for experimental implementation of complete braiding protocols, opening concrete pathways toward accessible non-abelian physics and topologically protected information processing.
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Strongly Correlated Electrons
Local-moment magnetism in Mn-based pnictides
Matteo Crispino, Niklas Witt, Tommaso Gorni et al. (+2 more)
We report a comprehensive study of electronic-correlation effects in Manganese-based
antiferromagnetic pnictides BaMn$_2$Pn$_2$ (Pn=P,As,Sb,Bi). Our density functional theory plus slave-
spin mean-field simulations indicate that all the compounds lie on the strong-coupling side of an itinerant-to-localized moment crossover, corresponding to the critical interaction strength for the Mott transition in the high-temperature paramagnetic phase. We also show that the experimental Néel temperature of each compound scales with the distance from this crossover.
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All authors Matteo Crispino, Niklas Witt, Tommaso Gorni, Giorgio Sangiovanni, Luca de' Medici
Quantum Gases
Controlled acoustic-driven vortex transport in coupled superfluid rings
A. Chaika, A. O. Oliinyk, I. V. Yatsuta et al. (+4 more)
Atomtronic
quantum sensors based on trapped superfluids offer a promising platform for high-precision inertial measurements where the dynamics of quantized
vortices can serve as sensitive probes of external forces. We analytically investigate persistent current oscillations between two density-coupled Bose-Einstein condensate rings and show that the
vortex dynamics is governed by low-energy acoustic excitations circulating through the condensate bulk. The oscillation frequency and damping rate are quantitatively predicted by a simplified hydrodynamic model, in agreement with Bogoliubov-de Gennes analysis and Gross-Pitaevskii simulations. We identify the critical dissipation separating persistent oscillations from overdamped
vortex localization. Furthermore, we demonstrate that periodic modulation of the inter-ring barrier at resonant frequencies enables controlled
vortex transfer even when the condensates are well separated in density. These results clarify the role of collective hydrodynamic modes in circulation transfer and establish a framework for employing
vortex dynamics in atomtronic
quantum technologies.
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All authors A. Chaika, A. O. Oliinyk, I. V. Yatsuta, M. Edwards, N. P. Proukakis, T. Bland, A. I. Yakimenko