Quantum Gases · Cross-listed from quant-ph
Analytically Continuing the Randomized Measurement Toolbox
Akash Vijay, Ayush Raj, Jonah Kudler-Flam et al. (+3 more)
We develop a framework for extracting non-
polynomial analytic functions of density
matrices in randomized measurement experiments by a method of analytical continuation. A central advantage of this approach, dubbed stabilized analytic continuation (SAC), is its robustness to statistical noise arising from finite repetitions of a
quantum experiment, making it well-suited to realistic
quantum hardware. As a demonstration, we use SAC to estimate the von Neumann
entanglement entropy of a numerically simulated quenched Néel state from Rényi
entropies estimated via the randomized measurement protocol. We then apply the method to experimental Rényi data from a trapped-ion
quantum simulator experiment, extracting subsystem von Neumann
entropies at different
evolution times. Finally, we briefly note that the SAC framework is readily generalizable to obtain other nonlinear diagnostics, such as the logarithmic negativity and Rényi relative
entropies.
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All authors Akash Vijay, Ayush Raj, Jonah Kudler-Flam, Benoît Vermersch, Andreas Elben, Laimei Nie
Statistical Mechanics
Revisiting Nishimori multicriticality through the lens of information measures
Zhou-Quan Wan, Xu-Dong Dai and Guo-Yi Zhu
The
quantum error correction threshold is closely related to the Nishimori physics of random statistical models. We extend
quantum information measures such as coherent information beyond the Nishimori line and establish them as sharp indicators of phase transitions over the full $p$-$T$ plane. These generalized measures admit a natural operational interpretation as diagnostics of inference mismatch for decoders operating at an effective temperature. We derive exact inequalities for several generalized measures, demonstrating that each attains its extremum along the Nishimori line. As a direct application, we study these measures in the 2d $\pm J$ random-bond Ising model-corresponding to a surface code under bit-flip noise-and revisit the Nishimori multicritical point. Among all indicators, coherent information exhibits the weakest finite-size effects, enabling a high-precision estimate $p_c=0.1092212(4)$ and the associated critical exponents.
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Statistical Mechanics · Cross-listed from quant-ph
Classical shadows for sample-efficient measurements of gauge-invariant observables
Jacob Bringewatt, Henry Froland, Andreas Elben et al. (+1 more)
Classical shadows provide a versatile framework for estimating many properties of
quantum states from repeated, randomly chosen measurements without requiring full
quantum state
tomography. When prior information is available, such as knowledge of
symmetries of states and operators, this knowledge can be exploited to significantly improve sample efficiency. In this work, we develop three classical shadow protocols for $\mathbb{Z}_2$
lattice gauge theory, where a dual formulation enables a rigorous analysis of resource requirements, including both
circuit depth and sample complexity. Our approaches can offer exponential improvements in sample complexity over
symmetry-agnostic methods, albeit at the cost of increased
circuit complexity. While our analysis is restricted to $\mathbb{Z}_2$
lattice gauge theory, our approach offers a blueprint for similar protocols for more general
lattice gauge theory models which are currently at the forefront of
quantum simulation efforts.
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All authors Jacob Bringewatt, Henry Froland, Andreas Elben, Niklas Mueller
Strongly Correlated Electrons · Cross-listed from quant-ph
Clifford Hierarchy Stabilizer Codes: Transversal Non-Clifford Gates and Magic
Ryohei Kobayashi, Guanyu Zhu and Po-Shen Hsin
A fundamental problem in fault-tolerant
quantum computation is the tradeoff between universality and dimensionality, exemplified by the the Bravyi-König bound for $n$-dimensional topological stabilizer codes. In this work, we extend topological Pauli stabilizer codes to a broad class of $n$-dimensional Clifford hierarchy stabilizer codes. These codes correspond to the $(n+1)$D Dijkgraaf-Witten gauge theories with non-Abelian topological order. We construct transversal non-Clifford gates through
automorphism symmetries represented by cup products. In 2D, we obtain the first transversal non-Clifford logical gates including T and CS for Clifford stabilizer codes, using the
automorphism of the twisted $\mathbb{Z}_2^3$ gauge theory (equivalent to $\mathbb{D}_4$ topological order). We also combine it with the just-in-time decoder to fault-tolerantly prepare the logical T magic state in $O(d)$ rounds via code switching. In 3D, we construct a transversal logical $\sqrt{\text{T}}$ gate in a non-Clifford stabilizer code at the third level of the Clifford hierarchy, located on a tetrahedron corresponding to a twisted $\mathbb{Z}_2^4$ gauge theory. Our constructions surpass the Bravyi-König bound by achieving the logical gates in the $(n+1)$-th level of Clifford hierarchy in $n$ spatial dimension.
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Strongly Correlated Electrons
Low-temperature entropies and possible states in geometrically frustrated magnets
Siyu Zhu, Arthur P. Ramirez and Sergey Syzranov
The
entropy that an insulating
magnetic material releases upon cooling can reveal important information about the properties of
spin states in that material. In many geometrically frustrated (GF)
magnetic compounds, the heat capacity exhibits a low-temperature peak that comes from the
spin states continuously connected to the ground states of classical models, such as the Ising model, on the same GF
lattice, which manifests in the amount of
entropy associated with this heat-capacity peak. In this work, we simulate numerically the values of
entropy released by higher-
spin triangular-
lattice layered systems and materials on SCGO
lattices. We also compare the experimentally measured values of
entropy in several strongly GF compounds, $NiGa_2S_4$, $FeAl_2Se_4$ and SCGO/BSZCGO, with possible theoretical values inferred from the classical models to which the
quantum states of those materials may be connected. This comparison suggests that the lowest-energy states of higher-
spin layered triangular-
lattice compounds can be described in terms of doublet states on individual
magnetic sites. Our analyses demonstrate how the values of
entropy can reveal the structure of low-energy
magnetic states in GF compounds and call for more accurate thermodynamic measurement in GF
magnetic materials.
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Quantum Gases
Structure and interactions of atoms and diatomic molecules: from ultracold gases to doped solids
Maxence Lepers
This is the manuscript of my "Habilitation à diriger des recherches", where I present the research work that I have done after my PhD, defended in 2009. The manuscript is divided in two parts. The first one is dedicated to atomic-structure calculations with neutral and trivalent lanthanides, in the contexts of ultracold gases and rare-earth doped solids. The second part deals with long-range interactions in ultracold gases of alkali-metal atoms and diatomic molecules, as well as lanthanide atoms. The detailed description of long-range interactions serves to characterize ultralow-temperature phenomena, like photoassociation and collisional shielding.
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Materials Science
A model for positron annihilation in multi-layer systems by solving the diffusion equation using different positron affinities
Lucian Mathes, Michael Göldl, Michael Leitner et al. (+5 more)
We present a method for solving the positron
diffusion equation in multi-layer systems. Our approach incorporates material-specific implantation profiles,
diffusion parameters, and positron affinities. It utilizes a Markov chain approach to model annihilation probabilities and provides fitting capabilities for experimental S (lineshape) parameter data. We have implemented this
algorithm in Python and made it available for free under the name LIMPID. To demonstrate its performance, we analyze depth-resolved Doppler-Broadening Spectroscopy measurements of a Cu layer on a Si substrate, achieving excellent agreement with the experimental profiles. The LIMPID tool enhances the reproducibility and comparability of positron defect characterization measurements across different research groups.
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All authors Lucian Mathes, Michael Göldl, Michael Leitner, Bettina Kohlhaas, Maximilian Suhr, Vassily Vadimovitch Burwitz, Armin Manhard, Christoph Hugenschmidt
Quantum Gases
Majorana string simulation of nonequilibrium dynamics in two-dimensional lattice fermion systems
Matteo D'Anna, Jannes Nys and Juan Carrasquilla
The study of real-time dynamics of
fermions remains one of the last frontiers beyond the reach of classical simulations and is key to our understanding of
quantum behavior in chemistry and materials, with implications for
quantum technology. Here we introduce a Heisenberg-picture
algorithm that propagates observables expressed in a Majorana-string basis using a truncation scheme that preserves Trotter accuracy and aims at maintaining computational efficiency. The framework is exact for quadratic
Hamiltonians – remaining restricted to a fixed low-weight sector determined by the physical observable – admits variational initial states, and can be extended to interacting regimes via systematically controlled truncations. We
benchmark our approach on one- and two-dimensional
Fermi-Hubbard quenches, comparing against tensor network methods (MPS and fPEPS) and recent experimental data. The method achieves high accuracy on timescales comparable to state-of-the-art variational techniques and experiments, demonstrating that controlled Majorana-string truncation is a practical tool for simulating two-dimensional fermionic dynamics.
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Mesoscale and Nanoscale Physics
Anomalous Hall effect in metallic collinear antiferromagnets
Vladimir P. Golubinskii and Vladimir A. Zyuzin
We propose and theoretically study minimal models of Néel ordered collinear (compensated) antiferromagnets that show the anomalous
Hall effect. For simplicity, we first consider two-dimensional models of antiferromagnets with two
magnetic sublattices on a square
lattice. We provide explicit examples of a Néel ordered ferrimagnet and a Dzyaloshinskii weak ferromagnet. Then antiferromagnet on the rutile
lattice, that belongs to the class of weak ferromagnets, is studied. We analyze Dzyaloshinskii's invariants for the existence of spontaneous magnetization in these Néel ordered systems. Microscopic calculations of the Berry
curvature for the studied systems confirm the validity of these Dzyaloshinskii's invariants. It is shown that the anomalous
Hall effect mechanism in these antiferromagnets arises either from the interplay of momentum-dependent exchange interaction of conducting
fermions with the Néel order and the
spin-orbit coupling. These physical processes originate from the broken
symmetries that permit the Dzyaloshinskii's invariant in the system.
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Strongly Correlated Electrons · Cross-listed from physics.chem-ph
From Densities to Potentials: Benchmarking Local Exchange-Correlation Approximations
Visagan Ravindran, Clio Johnson, Neil D. Drummond et al. (+2 more)
Using the Kohn-Sham (KS) inversion method of Hollins et al. [J. Phys.: Condens. Matter 29, 04LT01 (2017)], we invert densities from variational and
diffusion quantum Monte Carlo (QMC) calculations to obtain
benchmark QMC-KS potentials for a range of
insulators and
semiconductors, which we then compare to the KS potentials of popular density functional approximations (DFAs). Our results show that different DFAs yield similar electron densities, despite differences in their KS potentials, which originate primarily from the exchange and correlation contribution. We also find that the KS gap from the QMC density is typically larger than the KS gaps of most DFAs, with the exception of Hartree-Fock. Finally, the KS gap is sensitive to the inclusion of semicore states in the pseudopotentials, such that comparison with experiment should be done with caution.
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All authors Visagan Ravindran, Clio Johnson, Neil D. Drummond, Stewart J. Clark, Nikitas. I. Gidopoulos
Strongly Correlated Electrons
The two-dimensional optical Su-Schrieffer-Heeger model: ground state and thermodynamic properties
Jadson L. Portela e Silva, Gabriel Rein, Sebastião dos A. Sousa-Júnior et al. (+2 more)
We investigate the two-dimensional optical Su-Schrieffer-Heeger (SSH) model, in which the electron hopping amplitude is modulated by the difference between neighboring
phonon coordinates. Using sign-problem-free auxiliary-field
quantum Monte Carlo simulations, complemented by mean-field analysis, we determine the long-range ordered phases as a function of the electron-
phonon coupling and
phonon frequency. By examining both adiabatic and antiadiabatic regimes, we reveal the emergence of staggered and armchair valence bond solid (VBS) phases, as well as the O(4)
antiferromagnetic phase. In addition, finite-temperature simulations show that the VBS transition occurs at critical temperatures significantly higher than in models with local electron-
phonon coupling, consistent with the presence of lighter polarons in the metallic regime. These findings establish the ground-state and finite-temperature phase diagrams of the optical SSH model, which emphasize its similarities and contrasts with other electron-
phonon systems.
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All authors Jadson L. Portela e Silva, Gabriel Rein, Sebastião dos A. Sousa-Júnior, Fakher F. Assaad, Natanael C. Costa
Materials Science
Bandgap Engineering On Demand in GaAsN Nanowires by Post-Growth HydrogennImplantation
Nadine Denis, Akant Sharma, Elena Blundo et al. (+9 more)
Bandgap engineering in
semiconductors is required for the development of photonic and optoelectronic devices with optimized absorption and emission energies. This is usually achieved by changing the chemical or structural composition during growth or by dynamically applying strain. Here, the bandgap in GaAsN nanowires grown on Si is increased post-growth by up to 460 meV in a reversible, tunable, and non-destructive manner through H implantation. Such a bandgap tunability is unattained in epilayers and enabled by relaxed strain requirements in nanowire
heterostructures, which enables N concentrations of up to 4.2% in core-shell GaAs/GaAsN/GaAs nanowires resulting in a GaAsN bandgap as low as 0.97 eV. Using micro-photoluminescence measurements on individual nanowires, it is shown that the high bandgap energy of GaAs at 1.42 eV is restored by hydrogenation through formation of N-H complexes. By carefully optimizing the hydrogenation conditions, the photoluminescence efficiency increases by an order of magnitude. Moreover, by controlled thermal annealing, the large shift of the bandgap is not only made reversible, but also continuously tuned by breaking up N-H complexes in the hydrogenated GaAsN. Finally, local bandgap tuning by
laser annealing is demonstrated, opening up new possibilities for developing novel, locally and energy-controlled
quantum structures in GaAsN nanowires.
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All authors Nadine Denis, Akant Sharma, Elena Blundo, Francesca Santangeli, Paolo De Vincenzi, Riccardo Pallucchi, Mitsuki Yukimune, Alexander Vogel, Ilaria Zardo, Antonio Polimeni, Fumitaro Ishikawa, Marta DeLuca
Mesoscale and Nanoscale Physics
Model for charge carrier spectra in topological semimetals of the TaAs family
G. P. Mikitik and Yu. V. Sharlai
We propose a four-band model describing the electron energy spectra near the Weyl points in the topological semimetals of the TaAs family (TaAs, TaP, NbAs, NbP). This model takes into account the fact that these Weyl points result from the band-contact lines which would exist in the mirror-reflection planes of these materials if the
spin-orbit interaction were absent in them. Within this model, we obtain conditions for the existence of the Weyl points, determine their positions in the Brillouin zone, and derive the explicit formula for dispersion of the bands along the straight line connecting the two close Weyl points with opposite topological charges. Using NbP as an example, the values of the parameters defining the model spectrum are found. The obtained results show that for the semimetals of the TaAs family, the charge-carriers spectrum in the vicinity of the two close Weyl points can be analyzed without complex band-structure calculations.
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Mesoscale and Nanoscale Physics
Self-Consistent Theoretical Framework for Third-Order Nonlinear Susceptibility in CdSe/ZnS–MOF Quantum Dot Composites
Jingxu Wu, Yifan Yang, Jie Shi et al. (+3 more)
This work presents a fully theoretical and self consistent framework for calculating the third-order nonlinear susceptibility of CdSe/ZnS–MOF composite
quantum dots. The approach unifies finite-potential
quantum confinement,the Liouville von Neumann density
matrix expansion to third order, and effective-medium electrodynamics (Maxwell–Garnett and Bruggeman) within a single
Hamiltonian-based model, requiring no empirical fitting. Electron hole quantized states and dipole
matrix elements are obtained under the effective-mass approximation with BenDaniel–Duke boundary conditions; closed analytic forms for(including Lorentzian/Voigt broadening) follow from the response expansion. Homogenization yields macroscopic scaling laws that link microscopic descriptors (core radius, shell thickness, dielectric mismatch) to bulk coefficients and. A Kramers–Kronig consistency check confirms causality and analyticity of the computed spectra with small residuals. The formalism provides a predictive, parameter-transparent route to engineer third-order nonlinearity in hybrid
quantum materials,clarifying how size and environment govern the magnitude and dispersion of.
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All authors Jingxu Wu, Yifan Yang, Jie Shi, Yuwei Yin, Yifan He, Chenjia Li
Materials Science
Time-Reversed Superfluorescence in a Polaronic Quantum Material
Arnab Ghosh, Patrick Brosseau, Dmitry N. Dirin et al. (+2 more)
Superfluorescence, the cooperative burst of spontaneous emission from an ensemble of dipoles, arises when microscopic oscillators spontaneously synchronize their phases. Here we show that this process can be reversed in time within
quantum materials. Coherent multidimensional spectroscopy of halide perovskite
quantum dots reveals a delayed cooperative absorption burst, the mirror image of superfluorescent emission, driven by transient polaron fields that phase-lock unit-
cell dipoles within 100 fs. The effect scales systematically with
quantum-dot size and halide composition, reaching near-unity coherence fidelity even at 300 K. A microscopic
exciton-polaron model reproduces the buildup and decay of the coherent state, identifying
lattice polarons as the mediators of synchronization. These results demonstrate that many-body temporal coherence can self-organize and persist at room temperature, opening routes toward engineered collective optical states and superabsorbing
quantum devices.
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All authors Arnab Ghosh, Patrick Brosseau, Dmitry N. Dirin, Maksym V. Kovalenko, Patanjali Kambhampati
Quantum Gases
Angular momentum of rotating fermionic superfluids by Sagnac phonon interferometry
Marcia Frómeta Fernández, Diego Hernández Rajkov, Giulia Del Pace et al. (+5 more)
Fermionic many-body systems provide an unrivaled arena to investigate how interactions drive the emergence of collective
quantum behavior, such as macroscopic coherence and superfluidity. Central to these phenomena is the formation of Cooper pairs, correlated states of two
fermions that behave as composite
bosons and condense below a critical temperature. However, unlike elementary
bosons, these pairs retain their internal structure set by underlying fermionic correlations, essential for understanding superfluid properties throughout the so-called Bose-Einstein condensate (BEC) to Bardeen-Cooper-Schrieffer (BCS) crossover – a cornerstone of strongly correlated fermionic matter. Here, we harness a sonic analog of the optical Sagnac effect to disclose the composite nature of fermionic condensates across the BEC-BCS crossover. We realize an in-situ loop interferometer by coherently exciting two counter-propagating long-wavelength
phonons of an annular fermionic superfluid with tuneable interparticle interactions. The frequency degeneracy between clock- and anticlock-wise sound modes is lifted upon controllably injecting a quantized supercurrent in the superfluid ring, resulting in a measurable Doppler shift that enables us to probe the elementary
quantum of circulation and the angular momentum carried by each particle in the fermionic fluid. Our observations directly reveal that the superflow circulation is quantized in terms of $h/2m$, where $m$ is the mass of the constituents, in striking contrast to bosonic condensates where $h/m$ is the relevant circulation
quantum. Further, by operating our interferometer at tunable temperature, we measure the thermal depletion of the superfluid in the
unitary Fermi gas, demonstrating
phonon interferometry as a powerful technique for probing fundamental properties of strongly-correlated
quantum systems.
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All authors Marcia Frómeta Fernández, Diego Hernández Rajkov, Giulia Del Pace, Nicola Grani, Massimo Inguscio, Francesco Scazza, Sandro Stringari, Giacomo Roati
Other Condensed Matter
Exciton dynamics, Fano quantum interference and d-d excitation in the single crystal of two-dimensional antiferromagnetic Fe2P2S6
Nasaru Khan, Yuliia Shemerliuk, Sebastian Selter et al. (+3 more)
Excitonic quasiparticle and their interactions with
phonons,
magnons and charge carriers may play a pivotal role in governing the optical properties and their correlation with
magnetic interactions in two-dimensional (2D)
magnetic semiconductors. Further, in transition metal compounds, d-d electronic transitions, arising from excitations between
crystal-field split d-orbitals, significantly influence the optical and
magnetic properties, particularly in strongly correlated and low-dimensional systems. Fe2P2S6, a layered
antiferromagnetic semiconductor, offers a rich platform for studying the interplay between
spin, charge, and
lattice degrees of freedom in these 2D systems. In this work, we investigate the photoluminescence (PL) properties of Fe2P2S6 to probe the
exciton dynamics, intra-atomic transitions, and their temperature
evolution. Two prominent d-d emission peaks are observed at ~ 1.63 eV (D1) and ~ 1.80 eV (D2), attributed to the
crystal field-split Fe2+ states. An excitonic emission near the band edge is also identified, which exhibits a characteristic Fano asymmetric line shape. This asymmetry is attributed to the
quantum interference between the discrete excitonic state and the d-d transition induced continuum (D2), revealing a Fano resonance behaviour. This
exciton peak disappears well before the Neel temperature, indicating its faster destabilization than
magnetic ordering. Temperature-dependent PL measurements show a quenching of the excitonic peak with increasing temperature. Our findings provide detailed insight into the optical excitation pathways in Fe2P2S6.
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All authors Nasaru Khan, Yuliia Shemerliuk, Sebastian Selter, Bernd Buchner, Saicharan Aswartham, Pradeep Kumar
Strongly Correlated Electrons · Cross-listed from math.QA
Generalized Witt and Morita equivalences
Liang Kong, Yilong Wang and Hao Zheng
In this work, we introduce a family of new equivalence relations among fusion categories that are less refined than the usual Morita equivalence. We obtain abelian groups by quotienting these new equivalence relations from the commutative monoids of the equivalence classes of all fusion categories. Moreover, we upgrade them to equivalence relations among nondegenerate braided fusion categories that are more refined than the usual Witt equivalence. As a consequence, we obtain new abelian groups that are more refined than the usual Witt group. These new groups allow us to access the internal structures within Witt classes. We expect that they are useful in the classification program of (braided) fusion (higher) categories and in the study of gapless edges of 2+1D topological orders.
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Statistical Mechanics
Post-quench relaxation dynamics of Gross-Neveu lattice fermions
Domenico Giuliano, Reinhold Egger, Bidyut Dey et al. (+1 more)
We study the
quantum relaxation dynamics for a
lattice version of the one-dimensional (1D) $N$-
flavor Gross-Neveu (GN) model after a
Hamiltonian parameter quench. Allowing for a system-reservoir coupling $\gamma$, we numerically describe the system dynamics through a time-dependent self-consistent Lindblad master equation. For a closed ($\gamma=0$) finite-size system subjected to an interaction parameter quench, the order parameter dynamics exhibits oscillations and revivals. In the thermodynamic limit, our results imply that the order parameter reaches its post-quench stationary value in accordance with the eigenstate thermalization hypothesis (ETH). However, time-dependent finite-momentum correlation
matrix elements equilibrate only if $\gamma>0$. Our findings are consistent with the system being described by a pertinent Generalized Gibbs Ensemble (GGE) and, accordingly, highlight subtle yet important aspects of the post-quench relaxation dynamics of
quantum many-body systems.
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All authors Domenico Giuliano, Reinhold Egger, Bidyut Dey, Andrea Nava
Materials Science
Exploring mechanisms leading to composition errors in monazite (CePO4) analysed with atom probe tomography
Tom Veret, Fabien Delaroche, Ivan Blum et al. (+6 more)
Monazite (CePO4) is widely used in U-Th-Pb geochronology due to its reliable age determinations, although isotopic disturbances often require nanoscale investigation to better understand the mechanisms at play. Atom Probe
Tomography (APT) offers unique capabilities for nanoscale chemical analysis and 3D atomic reconstruction but presents challenges for insulating materials such as CePO4, particularly due to oxygen loss during field evaporation. This study investigates the effects of
laser wavelength, energy, metallic coatings and detection device on mass spectrum optimization and compositional accuracy in synthetic CePO4 samples. Results show that shorter
laser wavelengths (260 nm) enhance peak resolution, particularly when combined with advanced reflectron configurations, as demonstrated with the LEAP 6000 XR. Chromium coatings further improve thermal dissipation and reduce noise levels. However, compositional measurements reveal systematic underestimation of oxygen and overestimation of P and Ce, likely influenced by preferential low-field element evaporation. These findings highlight the need to carefully tune experimental parameters to mitigate quantification biases and enhance the reliability of APT analyses for geological materials.
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All authors Tom Veret, Fabien Delaroche, Ivan Blum, Jonathan Houard, Benjamin Klaes, Isabelle Mouton, Frederic De-Geuser, Anne-Magali Seydoux-Guillaume, François Vurpillot
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Emergent Bell Phase in an Electro-Nanomechanical Quantum Simulator
David Ullrich, Marta Cagetti, Stefan Forstner et al. (+2 more)
Suspended carbon nanotubes hosting electrostatically defined
quantum dots allow for exceptionally strong and tunable electromechanical coupling as well as mechanical modes that can reach the
quantum ground state of motion simply by cryogenic cooling. This makes them a unique platform for
quantum simulation of electron-
phonon coupling. Here, we propose an experimentally realisable setup with two such carbon nanotubes in parallel, each hosting four
quantum dots. Our system not only exhibits
phonon-mediated electron-electron attraction, but also supports a robust, maximally entangled Bell phase at mesoscopic scales shared across the subsystems. These features highlight its potential as a simulator of strongly correlated
quantum systems.
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All authors David Ullrich, Marta Cagetti, Stefan Forstner, Adrian Bachtold, Anna Sanpera
Materials Science
Suppression of auxetic behavior in black phosphorus with sulfur substitution
Hayden Groeschel, Arjyama Bordoloi and Sobhit Singh
Sulfur-doped black phosphorus (b-P) has recently emerged as a promising candidate for next-generation electronic and optoelectronic technologies owing to its enhanced environmental stability and tunable electronic properties. In this work, we systematically investigate the effects of sulfur substitution on the elastic, mechanical, and electronic properties of b-P, with a particular focus on its auxetic behavior (that is, negative Poisson's ratio), using first-principles density functional theory calculations. Our results unveil the fundamental origin of the intrinsic auxetic response in pristine b-P and elucidate how sulfur incorporation alters this behavior. We find that sulfur atoms distort the characteristic bow-tie structural motif responsible for the negative Poisson's ratio in b-P, thereby suppressing the in-plane auxeticity. Moreover, the resulting charge redistribution also effectively quenches the out-of-plane auxetic response of b-P. With increasing sulfur content, the bulk modulus and Poisson's ratio increase, whereas the Young's modulus, shear modulus, and Debye temperature decrease. Additionally, sulfur substitution suppresses the semiconducting properties of b-P, giving rise to
metallicity. These findings highlight that although sulfur substitution enhances the environmental stability of b-P, it also substantially modifies its elastic and mechanical properties, particularly the auxetic behavior, which is an important consideration in the design of nanoscale electronic devices.
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Mesoscale and Nanoscale Physics
Noises in a two-channel charge Kondo model
T. K. T. Nguyen, J. Rech, T. Martin et al. (+1 more)
We investigate fluctuations of electric and heat currents, along with their cross-correlations, in a two-channel charge Kondo
circuit driven by either a voltage bias or a temperature gradient applied across the weak link. The ratios of voltage-driven electric/heat noise to the applied voltage $V$ exhibit oscillations with the gate voltage $N$, resembling the behavior of the thermoelectric coefficient $G_T$. In contrast, the ratios of temperature-driven electric/heat noise to the temperature difference $\Delta T$ vary with $N$ in a manner analogous to the thermal coefficient $G_H$ or the electric conductance $G$. The mixed noise, which is defined as the correlation function between electric and heat currents, displays behavior opposite to that of the above noises. The logarithmic temperature dependence of these noises signals non-
Fermi-
liquid behavior, while their oscillations with gate voltage reflect the roles of particle-hole and time-reversal
symmetries in thermoelectric transport. Our results demonstrate that the fundamental relations linking voltage- and temperature-induced noises to thermoelectric transport across a tunnel junction persist beyond the
Fermi-
liquid paradigm.
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All authors T. K. T. Nguyen, J. Rech, T. Martin, M. N. Kiselev
Statistical Mechanics · Cross-listed from quant-ph
Collective Quantum Batteries and Charger-Battery Setup in Open Quantum Systems: Impact of Inter-Qubit Interactions, Dissipation, and Quantum Criticality
Mahima Yadav, Devvrat Tiwari and Subhashish Banerjee
Quantum batteries have emerged as promising platforms for exploring energy storage and transfer processes governed by
quantum mechanical laws. In this work, we study three models of two-
qubit open
quantum systems. The first model comprises two central
spins immersed in
spin baths, and both central
spins are collectively considered as
quantum batteries. The impact of inter-
qubit interactions on the performance of the
quantum battery is investigated. In the second model, a two-
qubit model interacting with a squeezed thermal bath serves as a collective
quantum battery, where the impact of inter-atomic distance and the bath temperature on the battery's performance is explored. Furthermore, a two-
qubit model is used, where one
qubit is modeled as a battery and the other as a charger. The charger in this model interacts with an anisotropic
spin-chain bath, which is conducive to
quantum criticality. It is demonstrated that this criticality has a substantial impact on the
quantum battery's storage capacity.
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Soft Condensed Matter
Universal behavior at the Lifshitz Points of an active Malthusian Ising model
Gabriel Legrand and Chiu Fan Lee
Lifshitz points (LPs) are multicritical points where ordered, disordered, and patterned phases meet. Originally studied in
equilibrium magnetic systems, LPs have since been identified in soft matter and even cosmological settings. Their role in active, living matter, however, remains entirely unexplored. Here we address this gap by introducing and analyzing LPs in the Active Malthusian Ising Model (AMIM) – a minimal model of living matter that incorporates motility together with birth-death dynamics. Despite its simplicity, the AMIM provides direct experimental relevance. We show that the system generically exhibits two distinct LPs and elucidate their universal behavior using a dynamic renormalization group analysis with the $\epsilon$-expansion method at one loop. Our results yield testable predictions for future simulations and experiments, establishing LPs as a fertile testing ground for novel physics in active matter.
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Materials Science
First-principles Prediction of Carrier Mobility in Semiconductor Nanowires Based on the Spatially Dependent Boltzmann Transport Equation
Zirui He, Shang-Peng Gao and Meng Chen
Carrier mobility in bulk
semiconductors is typically governed by electron-
phonon (e-ph) scattering. In nanostructures, spatial confinement can lead to significant surface scattering, lowering mobility and breaking the spatial homogeneity assumption of conventional models. In this work, a fully ab initio framework based on the spatially dependent Boltzmann transport equation for one-dimensional nanowires is developed. We apply it to Si and GaN assuming diffusive surface scattering, and reveal the mobility-diameter relation: $\mu_\mathrm{1D} = \mu_\mathrm{bulk} \left[1-\left(d/d_0\right)^{-\beta}\right]$. The parameter $d_0$, comparable to the carrier mean free path, defines a boundary layer exhibiting a considerable mobility gradient, and also quantifies the competition between e-ph and surface scattering together with $\beta$. We further discuss the effects of orientation, cross-sectional shape, and temperature. Moreover, experimental data are generally lower than our predictions, possibly due to structural imperfections, systematic errors from measurements, etc. Therefore, our theoretical method can provide an intrinsic
benchmark toward optimized experimental realizations.
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Statistical Mechanics
Haldane-Inspired Generalized Statistics
M. H. Naghizadeh Ardabili, Omid Yahyayi Monem, Morteza Nattagh Najafi et al. (+1 more)
We propose and study a generalized
quantum statistical framework, referred to as alpha statistics, that continuously interpolates between Bose–Einstein and
Fermi–Dirac statistics and naturally extends into the hyperbosonic regime for $\alpha < 0$. Inspired by Haldane's exclusion statistics, this formulation introduces a modified occupation weight function that encodes effective statistical interactions via the parameter $\alpha$. Using thermodynamic geometry, we analyze the sign and singular behavior of the thermodynamic
curvature as a diagnostic of underlying interactions and phase structures. A crossover temperature $T^{*}$, at which the
curvature changes sign, marks the transition between effectively attractive (Bose-like) and repulsive (
Fermi-like) statistical regimes. When expressed relative to the Bose–Einstein condensation temperature $T_{c}$, the ratio $T^{*}/T_{c}$ depends universally on $\alpha$. For negative $\alpha$, corresponding to hyperbosonic statistics, we find
curvature singularities at specific fugacities, indicating modified condensation phenomena distinct from conventional Bose condensation. These results highlight the
geometric and thermodynamic consequences of alpha statistics and establish a link between fractional exclusion principles and
curvature-induced interaction signatures in statistical thermodynamics.
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All authors M. H. Naghizadeh Ardabili, Omid Yahyayi Monem, Morteza Nattagh Najafi, Hosein Mohammadzadeh
Soft Condensed Matter · Cross-listed from math.OC
Non-Locally Controllable but Trackable Magnetic Head Flagellated Swimmer
Lucas Palazzolo, Mickaël Binois and Laëtitia Giraldi
Unlike macroscopic swimmers, microswimmers operate in a low-Reynolds-number regime dominated by viscous forces. This paper investigates the controllability of a
magnetic microswimmer composed of a spherical
magnetic head and an elastic, non-
magnetic flagellum. The swimmer evolves in a Stokes flow and is modeled using the resistive force theory. We prove that, under planar motion, the system is not small-time locally controllable and numerically identify regions that remain inaccessible. Nevertheless, simulations show that trajectory tracking can still be achieved via
Bayesian optimization, though it requires large-amplitude transverse deformations.
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Statistical Mechanics · Cross-listed from hep-th
A JT/KPZ correspondence
Masataka Watanabe
We point out a correspondence between the Jackiw–Teitelboim (JT)
gravity and the stationary measure of the Kardar–Parisi–Zhang (KPZ) equation on an interval. By relating the Schwarzian limit of the double-scaled SYK to the weakly asymmetric limit of the open ASEP, we establish that the path-integral measure defining the Euclidean
evolution between two end-of-the-world branes in JT
gravity can be interpreted as the stationary measure of the KPZ equation on an interval with Neumann boundary conditions. We also establish the match between correlation functions.
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Mesoscale and Nanoscale Physics
Theory of In-Plane-Magnetic-Field-Dependent Excitonic Spectra in Atomically Thin Semiconductors
Michiel Snoeken, Paul Steeger, Robert Schmidt et al. (+4 more)
The linear absorption spectrum of
excitons in TMDC monolayers under the influence of an in-plane
magnetic field is theoretically studied. We demonstrate that in-plane
magnetic fields induce a hybridization between
spin-bright and
spin-dark
exciton transitions, resulting in a brightening of
spin-dark
excitons. We analytically investigate spectral features including resonance energy shifts, broadening and amplitudes ratios. In particular, for a MoSe$_2$ monolayer with radiatively-limited linewidth, we find a complex interplay of dark-bright splitting and linewidth difference of both involved
spin-bright and
spin-dark
excitons.
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All authors Michiel Snoeken, Paul Steeger, Robert Schmidt, Steffen Michaelis de Vasconcellos, Rudolf Bratschitsch, Andreas Knorr, Henry Mittenzwey