Publications

2025

• Return-Time Point Processes in Finite and Infinite Measure-Preserving Dynamical Systems
  
  • Bansard-Tresse Dylan
  , 2025. This thesis is devoted to the study of the statistical properties of discrete-time dynamical systems. Such a system is defined by a phase space on which acts a dynamics, and is often equipped with an invariant measure. The aim of ergodic theory is to understand the asymptotic behaviour of typical orbits. We are particularly interested here in the statistics of successive hitting and return times to subsets of the phase space. For a fixed target set, the hitting time refers to the time it takes for a generic orbit to enter the set, while the return time corresponds to the first recurrence of a point originating from the set back to itself.In the case where the measure is finite and the system ergodic, Poincaré's recurrence theorem ensures that these times are finite almost surely and Kac's theorem guarantees that the expectation of the return time is the inverse of the target measure. The theory of return and hitting time statistics is concerned with studying fluctuations around this mean, particularly when considering a sequence of targets whose measure goes to zero. For sufficiently chaotic systems, typically uniformly expanding, and natural targets (typically dynamically defined balls or cylinders) centered at generic points, it is known that the limiting law of hitting times is exponential, and the distribution of successive returns converges towards a Poisson point process. This universal behavior extends to all non-periodic points. On the other hand, for periodic points, a convergence to a compound Poisson process is observed. We show that this property is still verified for new examples of non-uniformly hyperbolic systems such as the family of logistic maps with Misiurewicz parameters. To do this, we rely mainly on a generalized inducing method.The main focus of this thesis is the analysis of these phenomena in the setting of dynamical systems preserving an infinite measure. In this context, the ergodic properties differ profoundly from those of the finite case, and the limit behaviors observed are distinct. For pointwise dual ergodic systems, we establish the equivalence between hitting and return rare event point processes, highlighting the emergence of the fractional Poisson process, a natural analogue of the standard Poisson point process in infinite measure. By exploiting this abstract equivalence between hitting and return times, we obtain convergence results for point processes associated to natural targets shrinking to a point in the phase space. For intermittent maps of the interval, we determine the limit laws for all points. In addition to fractional Poisson processes, we show convergence to compound versions for periodic points, and we also identify a third, novel class of limit processes, specific to infinite measure and presenting new characteristics.For the paradigmatic class of topological Markov shifts, including in particular Markov chains on a countable state space, we carry out a similar study, and characterize in detail the different types of point processes that can appear. In particular, we show that certain systems, such as Z-extensions over strong positive recurrent Markov shifts, do not give rise to this new class of limit processes for nested sequences of asymptotically rare balls.Finally, we address the question of limit laws for Birkhoff sums of natural observables with a singularity. Using connection with extreme value theory, we link this problem to that of spatio-temporal rare event point processes, which we explore here for the first time in infinite measure. This allows us to broaden the trichotomy previously observed and to derive a generalization of functional stable limit theorems in the framework of infinite measure-preserving dynamical systems. Furthermore, for sequences of centered topological balls converging to non-typical points, we show that spatio-temporal processes can converge to limit processes presenting correlations between the spatial and the temporal components. (10.70675/d45faf1bzb1bcz4129z8a87z68244e4aaade)
  DOI : 10.70675/d45faf1bzb1bcz4129z8a87z68244e4aaade
• First-Principles Analysis of Carrier Transport and Vibrational Properties in Pyrite-Structured Transition Metal Chalcogenides
  
  • Mukherjee Anustup
  , 2025. This thesis presents a detailed first-principles study of the thermoelectric transport properties of selected transition metal chalcogenides crystallizing in the pyrite structure.These materials are of significant interest due to their earth-abundance, chemical stability, and promising potential for application in energy conversion and storage technologies, suchas thermoelectrics, photovoltaics, catalysis, and batteries.Chapters 1 and 2 lay the groundwork by introducing the fundamental concepts of thermoelectricity, providing an overview of pyrite-structure based materials, and describing the computa-tional methods employed. This foundation supports the detailed analysis of electronic and transport properties in the subsequent chapters.Chapter 3 investigates the evolution of the electronic structurein Co1−xFexS2 with increasing Fe content. Despite variationsacross exchange-correlation functionals, a consistent trend ofbroadening in the lowest-lying minority-spin conduction bandsand a reduction in exchange-splitting is observed as the com-position approaches stoichiometric FeS2. These results, alongwith photoemission spectroscopic evidence showing occupied minority-spin states at the Fermi level in pure CoS2, confirm thepresence of minority-spin states throughout the series, contra-dicting earlier theoretical predictions.Chapter 4, motivated by discrepancies in reported room-temperature thermopower in self- and Co-doped FeS2, analyzes electron-doped FeS2 using explicit Co-substitution, jellium doping, and Fermi level shift within the rigid band approximation. Chapter 5 extends this analysis to hole doping, incorporating electron-phonon scattering. In both cases, the predicted thermoelectric performance indicates that doped FeS2 isunlikely to serve as an efficient thermoelectric material.Finally, Chapter 6 presents a comparative thermal transportstudy of two isoelectronic pyrites, FeS2 and RuS2. RuS2 ex-hibits lower room-temperature lattice thermal conductivity, attributed to reduced phonon velocities due to the heavier Ruatoms and increased anharmonic phonon scattering. Thesefindings underscore the influence of atomic mass and anhar-monicity in governing thermal transport in pyrite systems. (10.70675/df258364zf8c7z418ez8c9czbcc9d953481b)
  DOI : 10.70675/df258364zf8c7z418ez8c9czbcc9d953481b
• First-Principles Analysis of Carrier Transport and Vibrational Properties in Pyrite-Structured Transition Metal Chalcogenides
  
  • Mukherjee Anustup
  , 2025. This thesis presents a detailed first-principles study of the thermoelectric transport properties of selected transition metal chalcogenides crystallizing in the pyrite structure.These materials are of significant interest due to their earth-abundance, chemical stability, and promising potential for application in energy conversion and storage technologies, suchas thermoelectrics, photovoltaics, catalysis, and batteries.Chapters 1 and 2 lay the groundwork by introducing the fundamental concepts of thermoelectricity, providing an overview of pyrite-structure based materials, and describing the computa-tional methods employed. This foundation supports the detailed analysis of electronic and transport properties in the subsequent chapters.Chapter 3 investigates the evolution of the electronic structurein Co1−xFexS2 with increasing Fe content. Despite variationsacross exchange-correlation functionals, a consistent trend ofbroadening in the lowest-lying minority-spin conduction bandsand a reduction in exchange-splitting is observed as the com-position approaches stoichiometric FeS2. These results, alongwith photoemission spectroscopic evidence showing occupied minority-spin states at the Fermi level in pure CoS2, confirm thepresence of minority-spin states throughout the series, contra-dicting earlier theoretical predictions.Chapter 4, motivated by discrepancies in reported room-temperature thermopower in self- and Co-doped FeS2, analyzes electron-doped FeS2 using explicit Co-substitution, jellium doping, and Fermi level shift within the rigid band approximation. Chapter 5 extends this analysis to hole doping, incorporating electron-phonon scattering. In both cases, the predicted thermoelectric performance indicates that doped FeS2 isunlikely to serve as an efficient thermoelectric material.Finally, Chapter 6 presents a comparative thermal transportstudy of two isoelectronic pyrites, FeS2 and RuS2. RuS2 ex-hibits lower room-temperature lattice thermal conductivity, attributed to reduced phonon velocities due to the heavier Ruatoms and increased anharmonic phonon scattering. Thesefindings underscore the influence of atomic mass and anhar-monicity in governing thermal transport in pyrite systems.
• Spin-polaron fingerprints in the optical conductivity of iridates
  
  • Cassol Francesco
  • Gaspard Léo
  • Martins Cyril
  • Casula Michele
  • Lenz Benjamin
  Physical Review B, American Physical Society, 2025, 113 (24), pp.L241107. As a consequence of their spin-orbit entangled ground state, many $5d^{5}$ iridate materials display a peculiar double peak structure in optical transport quantities, such as absorption and conductivity. Their common interpretation is based on the presence of Hubbard subbands in the half-filled $j_{\mathrm{eff}}=1/2$ manifold. Herein, we challenge this picture, proposing a scenario based on the presence of spin-polaron (SP) quasiparticles, and assigning a dominant SP character to the first peak. We illustrate it by taking the materials Ba$_2$IrO$_4$ and Sr$_2$IrO$_4$ as paradigmatic examples, which we investigate within the dynamical mean-field theory and the self-consistent Born approximation. Both theories reproduce nontrivial features revealed by angle-resolved photoemission spectroscopy and optical transport measurements, supporting our interpretation. In the case of Sr$_2$IrO$_4$, we show how the SP scenario survives in the low-doped regime. Similar optical transport fingerprints are expected to be found in the wider class of $5d^5$ iridates and more generally in strongly correlated antiferromagnetic regimes, such as those found in cuprates. (10.1103/xt5x-8c92)
  DOI : 10.1103/xt5x-8c92
• State of the art of gyrokinetic and hybrid MHD-kinetic codes through non-linear benchmarking to study reactor relevant burning plasmas
  
  • Vlad Gregorio
  • Wang Xin
  • Vannini Francesco
  • Lütjens Hinrich
  • Briguglio Sergio
  • Carlevaro Nakia
  • Falessi Matteo
  • Fogaccia Giuliana
  • Fusco Valeria
  • Zonca Fulvio
  • Biancalani Alessandro
  • Bottino Alberto
  • Hayward-Schneider Thomas
  • Lauber Philipp
  • Rofman Baruch
  • Villard Laurent
  Reviews of Modern Plasma Physics, Springer Singapore, 2025, 9 (1), pp.27. Abstract After a brief introduction on present day simulation and modeling of burning plasmas in magnetically confined devices, the results of a non-linear benchmark are presented, undertaken among several state-of-the-art codes available to study the self-consistent interaction of an Energetic Particle (EP) population with shear Alfvén waves: HYMAGYC, MEGA, ORB5 and XTOR-K. The first two codes, HYMAGYC and MEGA, are hybrid codes: HYMAGYC is a MHD-Gyrokinetic code (the bulk plasma is represented by MHD equations, while the EP species is treated using the gyrokinetic formalism), while MEGA is an MHD-Drift-Kinetic code (the bulk plasma is represented by MHD equations, while the EP species is treated using the drift-kinetic formalism, with the possibility of an ad-hoc gyroaveraging); ORB5 is a global electromagnetic gyrokinetic code (both bulk and EP species are treated using the gyrokinetic formalism); XTOR-K is a non-linear kinetic-MHD code (the bulk plasma is described by a set of non-linear resistive two-fluid MHD equations, extended to include kinetic effects of multiple ion species with a fully kinetic PIC module). The equilibrium of the so-called NLED-AUG reference case, in its version with peaked off-axis EP density profile, has been used, while considering a | n | = 1 perturbation. This non-linear benchmark is the natural continuation of the linear benchmark already considered in the recent past, and represent a first-ever code comparison in the deep non-linear stage. In the present study fluid non-linearities are omitted, and the focus will be on comparing wave-particle interactions effects across codes. Characteristics of the non-linear saturation of the mode, self-consistent modification to the EP density profile and other features are compared among the considered codes. This brief review presents the state of the art of gyrokinetic and hybrid MHD-kinetic codes emerging as tools for studying reactor-relevant burning plasmas in realistic conditions. (10.1007/s41614-025-00199-2)
  DOI : 10.1007/s41614-025-00199-2
• Functional Limit Theorems for the range of stable random walks
  
  • Baccara Maxence
  , 2025. <div><p>In this paper we establish Functional Limit Theorems for the range of random walks in Z d that are in the domain of attraction of a non-degenerate β-stable process in the weakly transient and recurrent regimes. These results complement the fluctuations obtained at fixed time and the functional limit Theorems obtained in the strongly transient regime.</p><p>The techniques involve original ideas of Le Gall and Rosen for fluctuations and allow to show tightness in some Hölder space, thus also providing sharp regularity results about the limiting processes.</p><p>The original motivation of this work is the description of functionals appearing in spatial ecology for consumption of resources induced by random motion. We apply our result to estimate the large fluctuations of energy and mortality for a simple prey predator model.</p></div>
• Phase transitions and remnants of fractionalization at finite temperature in the triangular lattice quantum loop model
  
  • Ran Xiaoxue
  • Capponi Sylvain
  • Rong Junchen
  • Alet Fabien
  • Meng Zi Yang
  Physical Review Letters, American Physical Society, 2025, 135 (12), pp.126503. The quantum loop model (QLM), along with the quantum dimer model (QDM), are archetypal correlated systems with local constraints. With natural foundations in statistical mechanics, these models are of direct relevance to various important physical concepts and systems, such as topological order, lattice gauge theories, geometric frustrations, or more recently Rydberg quantum simulators. However, the effect of finite temperature fluctuations on these quantum constrained models has been barely explored. Here we study, via unbiased quantum Monte Carlo simulations and field theoretical analysis, the finite temperature phase diagram of the QLM on the triangular lattice. We discover that the vison plaquette (VP) crystal experiences a finite temperature continuous transition, which smoothly connects to the (2+1)d Cubic* quantum critical point separating the VP and $\mathbb{Z}_{2}$ quantum spin liquid phases. This finite temperature phase transition acquires a unique property of {\it thermal fractionalization}, in that, both the cubic order parameter -- the plaquette loop resonance -- and its constituent -- the vison field -- exhibit independent criticality signatures. This phase transition is connected to a 3-state Potts transition between the lattice nematic phase and the high-temperature disordered phase. (10.1103/tp8x-dscx)
  DOI : 10.1103/tp8x-dscx
• On the Gaussian distribution of the Mann-Kendall tau in the case of autocorrelated data
  
  • Gamot Tristan
  • Thibeau--Sutre Nils
  • van Dooren Tom
  , 2025. Non-parametric Mann-Kendall tests for autocorrelated data rely on the assumption that the distribution of the normalized Mann-Kendall tau is Gaussian. While this assumption holds asymptotically for stationary autoregressive processes of order 1 (AR(1)) and simple moving average (SMA) processes when sampling over an increasingly long period, it often fails for finite-length time series. In such cases, the empirical distribution of the Mann-Kendall tau deviates significantly from the Gaussian distribution. To assess the validity of this assumption, we explore an alternative asymptotic framework for AR(1) and SMA processes. We prove that, along upsampling sequences, the distribution of the normalized Mann-Kendall tau does not converge to a Gaussian but instead to a bounded distribution with strictly positive variance. This asymptotic behavior suggests scaling laws which determine the conditions under which the Gaussian approximation remains valid for finite-length time series generated by stationary AR(1) and SMA processes. Using Shapiro-Wilk tests, we numerically confirm the departure from normality and establish simple, practical criteria for assessing the validity of the Gaussian assumption, which depend on both the autocorrelation structure and the series length. Finally, we illustrate these findings with examples from existing studies. (10.48550/arXiv.2508.10842)
  DOI : 10.48550/arXiv.2508.10842
• Backward DVCS in a Sullivan process
  
  • Castro Abigail
  • Mezrag Cédric
  • Chávez Jose
  • Pire Bernard
  Physical Review D, American Physical Society, 2025, 112 (3), pp.034009. Mesons' internal structure and dynamics may be accessed through hard exclusive electroproduction processes such as deeply virtual Compton scattering in both near forward and near backward kinematics. With the help of the Sullivan process which allows us to use a nucleon target as a quasi-real pi meson emitter, we study backward scattering in the framework of collinear QCD factorization where pion-to-photon transition distribution amplitudes describe the photon content of the pi meson. We present a model of these TDAs based on the overlap of lightfront wave functions primarily developed for generalized parton distributions, using a previously developed pion lightfront wave function and deriving a new model for the lightfront wave functions of the photon. This leads us to an estimate of the cross-sections for JLab energies. We conclude that deeply virtual e p \rightarrow e gamma M n processes, in backward kinematics, may be experimentally discovered in the near future. (10.1103/y9rw-b2xj)
  DOI : 10.1103/y9rw-b2xj
• Learning interactions between Rydberg atoms
  
  • Simard Olivier
  • Dawid Anna
  • Tindall Joseph
  • Ferrero Michel
  • Sengupta Anirvan
  • Georges Antoine
  PRX Quantum, APS Physics, 2025, 6 (3), pp.030324. Quantum simulators have the potential to solve quantum many-body problems that are beyond the reach of classical computers, especially when they feature long-range entanglement. To fulfill their prospects, quantum simulators must be fully controllable, allowing for precise tuning of the microscopic physical parameters that define their implementation. We consider Rydberg-atom arrays, a promising platform for quantum simulations. Experimental control of such arrays is limited by the imprecision on the optical tweezers positions when assembling the array, hence introducing uncertainties in the simulated Hamiltonian. In this work, we introduce a scalable approach to Hamiltonian learning using graph neural networks (GNNs). We employ the Density Matrix Renormalization Group (DMRG) to generate ground-state snapshots of the transverse field Ising model realized by the array, for many realizations of the Hamiltonian parameters. Correlation functions reconstructed from these snapshots serve as input data to carry out the training. We demonstrate that our GNN model has a remarkable capacity to extrapolate beyond its training domain, both regarding the size and the shape of the system, yielding an accurate determination of the Hamiltonian parameters with a minimal set of measurements. We prove a theorem establishing a bijective correspondence between the correlation functions and the interaction parameters in the Hamiltonian, which provides a theoretical foundation to our learning algorithm. Our work could open the road to feedback control of the positions of the optical tweezers, hence providing a decisive improvement of analog quantum simulators. (10.1103/f58h-zxs3)
  DOI : 10.1103/f58h-zxs3
• Long time behavior and Yaglom limit for real trait-structured Birth and Death Processes
  
  • Collet Pierre
  • Méléard Sylvie
  • San Jaime
  , 2025. In this article we study the long time behaviour of measure-valued birth and death processes in continuous time, where the dynamics between jumps are one-dimensional Markov processes including diffusion and jumps. We consider the three regimes, critical, subcritical and supercritical. Under suitable hypotheses on the Feynman-Kac semigroup, we prove a new recurrence for the moments and the extinction probability, their time asymptotics and the convergence in law for the measure-valued birth and death process conditioned to non extinction, leading to the existence of Q-process and Yaglom limit (in this infinite dimensional setting). We develop three classes of natural examples where our results apply.
• Baryon-antibaryon generalized distribution amplitudes and $e^+ e^- \to B \bar{B} \gamma$
  
  • Han Jing
  • Pire Bernard
  • Song Qin-Tao
  Physical Review D, American Physical Society, 2025, 112, pp.014048. Baryon-antibaryon generalized distribution amplitudes (GDAs) give an access to timelike gravitational form factors (GFFs) which are complementary to the spacelike ones which can be deduced from the hadronic generalized parton distributions (GPDs) measured in deep exclusive electroproduction processes. They allow to probe the GFFs of unstable baryons in the baryon octet, since the second moments of hadronic generalized distribution amplitudes (GDAs) lead to the timelike GFFs. These GDAs can be measured in the process $e^+ e^- \to B \bar{B} \gamma$, in the generalized Bjorken regime where the invariant mass of the $B \bar{B}$ pair is near threshold at high energy facilities, such as BESIII, Belle II, and the proposed Super Tau-Charm Facility. In this work, we investigate this process using the QCD collinear factorization framework, where the scattering amplitudes are expressed in terms of the baryon timelike electromagnetic (EM) FFs and Compton FFs. We also provide a numerical estimate of the cross sections with a model for baryon-antibaryon GDAs. Our work provides us a possibility to extract the timelike baryon GFFs from near future experimental measurements, and these GFFs may be further used to study longstanding questions in hadronic physics such as the baryon spin decomposition and D-term. (10.1103/p8k5-rrzs)
  DOI : 10.1103/p8k5-rrzs
• Hidden orders in spin–orbit-entangled correlated insulators
  
  • Pourovskii Leonid
  • Fiore Mosca Dario
  • Celiberti Lorenzo
  • Khmelevskyi Sergii
  • Paramekanti Arun
  • Franchini Cesare
  Nature Reviews Materials, Springer Nature, 2025, 10 (9), pp.674-696. <div xmlns="http://www.tei-c.org/ns/1.0"><p>In many materials, ordered phases and their order parameters are easily characterized by standard experimental methods. "Hidden order" refers to a phase transition in which an ordered state emerges without such an easily detectable order parameter, despite clear thermodynamic evidence of the transition. The underlying mechanisms for these unconventional states of matter stem from spin-orbit coupling, which intertwines inter-site exchange, classical electromagnetic interactions, and electron-lattice effects. This physics is elusive to experimental probes and beyond traditional theories of insulating magnetism, requiring sophisticated methodologies for its exploration. In this Review, we survey exotic hidden-order phases in correlated insulators, particularly focusing on the latest progress in material-specific theories and numerical approaches. The relevant degrees of freedom in these phases are local high-rank multipole moments of magnetic and charge density that emerge from spin-orbit entangled correlated shells of heavy d and f electron ions and interact on the lattice via various mechanisms. We discuss approaches to modelling hidden orders in realistic systems via direct ab initio calculations or by constructing low-energy many-body effective Hamiltonian. We also describe how these new theoretical tools have helped to uncover driving mechanisms for recently discovered multipolar phases in double perovskites of heavy transition metals, and how they have proved instrumental in disentangling the role of various interactions in "traditional" f -electron multipolar materials like actinide dioxides. In both cases, material-specific theories have played a key role in interpreting and predicting experimental signatures of hidden orders.</p></div> (10.1038/s41578-025-00824-z)
  DOI : 10.1038/s41578-025-00824-z
• Fingerprints of a charge ice state in the doped Mott insulator Nb3⁢Cl8
  
  • Stepanov Evgeny
  Physical Review B, American Physical Society, 2025, 112, pp.045131. The interplay between strong electronic correlations and the inherent frustration of certain lattice geometries is a common mechanism for the formation of nontrivial states of matter. In this work, we theoretically explore the collective electronic effects in the monolayer Nb$_3$Cl$_8$, a recently discovered triangular lattice Mott insulator. Our advanced many-body numerical simulations predict the emergence of a phase separation region upon doping this material. Notably, in close proximity to the phase separation, the static charge susceptibility undergoes a drastic change and reveals a distinctive bow-tie structure in momentum space. The appearance of such a signature in the context of spin degrees of freedom would indicate the formation of a spin ice state. This finding allows us to associate the observed phase separation to a charge ice state, a state with a remarkable power-law dependence of both the effective exchange interaction and correlations between electronic densities in real space. (10.1103/j6bj-gz7j)
  DOI : 10.1103/j6bj-gz7j
• Antiferro octupolar order in the 5 d 1 double perovskite Sr 2 MgReO 6 and its spectroscopic signatures
  
  • Fiore Mosca Dario
  • Pourovskii Leonid V
  Physical Review Research, American Physical Society, 2025, 7 (3), pp.L032016. “Hidden”-order phases with high-rank multipolar order parameters have been recently detected in several cubic double perovskites of 5 d transition metals. Here, by constructing and solving an low-energy Hamiltonian, we show that an antiferroic order of magnetic octupoles also forms in the tetragonal 5 d 1 double perovskite Sr 2 MgReO 6 . The low-temperature order in this material is determined by a tetragonal crystal field dominating over exchange interactions. This results in a well isolated crystal-field doublet ground state hosting octupolar low-energy degrees of freedom. Very weak dipole moments entangled with the primary octupole order parameters are induced by admixture of the excited j 1 / 2 spin-orbit multiplet. We show that the octupolar order leads to characteristic quasigapless magnetic excitation spectra, as well as to the intensity of superstructural neutron diffraction reflexes peaking at large scattering momenta. (10.1103/tvp5-mpy9)
  DOI : 10.1103/tvp5-mpy9
• Toward an advanced phenomenology of pi N transition distribution amplitudes
  
  • Pire B.
  • Semenov-Tian-Shansky K.
  • Sznajder P.
  • Szymanowski L.
  Physical Review D, American Physical Society, 2025, 112, pp.014023. We introduce a new approach to modeling transition distribution amplitudes (TDAs) for the processes e p to e n pi+ and e p to e p pi0. The modeling is flexible, constrained by sparsely available experimental data, and satisfies theoretical requirements, including reduction to nucleon distribution amplitudes in the appropriate limit. We study the sensitivity of observable predictions to various modeling assumptions. We discuss unpolarized cross-sections, as well as the three non-vanishing polarization observables at leading twist, namely, the single transverse target spin asymmetry and the two double spin asymmetries that occur with a polarized lepton beam on either a longitudinally or transversely polarized target. The analysis is complemented by a simple Monte Carlo study to provide guidance for exploring exclusive processes in the so-called backward kinematics. Our work aims to highlight the importance of future measurements to better constrain TDAs and to support upcoming experimental proposals. (10.1103/6gc4-vnk9)
  DOI : 10.1103/6gc4-vnk9
• Saisir la polyvocalité des archives audiovisuelles et numériques en contexte post-colonial
  
  • Gebeil Sophie
  • Savéant Pauline
  • Mussard Christine
  • Ginouvès Véronique
  • Peyssard Jean-Christophe
  • Génois -Cpt Mathieu
  • Jakubiec-Jamet Line
  • Bellot Patrice
  , 2025. Ce document est le bilan du travail de l'équipe française dans le cadre du programme européen PICCH. L'objectif global du PICCH est d'engendrer une polyvocalité qui peut être incorporée dans l'archive elle-même, offrant de nouvelles façons d'entrer et d'explorer le passé par le biais d'un cadre interprétatif contemporain. À cet effet, des technologies de pointe seront utilisées pour étudier comment faire le lien entre les langues archivistiques et contemporaines, et pour soutenir l'exploration transnationale de plusieurs archives via une seule interface utilisateur interactive.
• Toward Numerically Exact Computation of Conductivity in the Thermodynamic Limit of Interacting Lattice Models
  
  • Kovačević Jeremija
  • Ferrero Michel
  • Vučičević Jakša
  Physical Review Letters, American Physical Society, 2025, 135 (1), pp.016502. (10.1103/mm38-zttx)
  DOI : 10.1103/mm38-zttx
• Using net quark number gain to probe the phases of QCD
  
  • Mari Surkau V. Tomas
  • Reinosa Urko
  , 2025. We discuss an observable that probes the content of a QCD medium at finite temperature and chemical potential, the net quark number gain. It is the response of the thermal bath to a static quark or antiquark probe. While insignificant at high temperatures, it reveals the bath's tendency to form meson-like or baryon-like configurations (depending on the probe and chemical potential) at low temperatures, which would screen the probe's color charge. The net quark number gain also helps explain how a single quark/antiquark can be added to a supposedly confining medium in the first place: the latter provides the missing quarks/antiquarks to form hadron-like states. We sketch the derivation of this general result for temperatures much smaller than the constituent quark masses and discuss possible further applications to study the various features of the QCD phase diagram.
• Turning qubit noise into an advantage: Automatic state preparation and long-time dynamics for impurity models on quantum computers
  
  • Bertrand Corentin
  • Besserve Pauline
  • Ferrero Michel
  • Ayral Thomas
  Physical Review B, American Physical Society, 2025, 111 (24), pp.245159. Noise is often regarded as a limitation of quantum computers. In this work, we show that in the dynamical mean-field theory (DMFT) approach to strongly correlated systems, it can actually be harnessed to our advantage. Indeed, DMFT maps a lattice model onto an impurity model, namely, a finite system coupled to a dissipative bath. While standard approaches require a large number of high-quality qubits in a unitary context, we propose a circuit that harvests amplitude damping to reproduce the dynamics of this model with a blend of noisy and noiseless qubits. We find compelling advantages with this approach: a substantial reduction in the number of qubits, the ability to reach longer time dynamics, and no need for ground-state search and preparation. This method would naturally fit in a partial quantum error correction framework. (10.1103/g1ky-4zd7)
  DOI : 10.1103/g1ky-4zd7
• Uncovering Hidden Orders within Deformable Materials: The Case of Dysprosium
  
  • Qiao Zeyu
  • Lin Kun
  • Khmelevskyi Sergii
  • Pourovskii Leonid
  • Xu Hankun
  • He Meng
  • Yu Chengyi
  • Cao Yili
  • Li Qiang
  • Xing Xianran
  Journal of the American Chemical Society, American Chemical Society, 2025, 147 (26), pp.23026-23033. (10.1021/jacs.5c06003)
  DOI : 10.1021/jacs.5c06003
• Distributed Quantum Advantage for Local Problems
  
  • Balliu Alkida
  • Brandt Sebastian
  • Coiteux-Roy Xavier
  • d'Amore Francesco
  • Equi Massimo
  • Le Gall François
  • Lievonen Henrik
  • Modanese Augusto
  • Olivetti Dennis
  • Renou Marc-Olivier
  • Suomela Jukka
  • Tendick Lucas
  • Veeren Isadora
  , 2025, pp.451-462. We present the first local problem that shows a super-constant separation between the classical randomized LOCAL model of distributed computing and its quantum counterpart. By prior work, such a separation was known only for an artificial graph problem with an inherently global definition [Le Gall et al. 2019]. We present a problem that we call iterated GHZ, which is defined using only local constraints. Formally, it is a family of locally checkable labeling problems [Naor and Stockmeyer 1995]; in particular, solutions can be verified with a constant-round distributed algorithm. We show that in graphs of maximum degree $\Delta$, any classical (deterministic or randomized) LOCAL model algorithm will require $\Omega(\Delta)$ rounds to solve the iterated GHZ problem, while the problem can be solved in $1$ round in quantum-LOCAL. We use the round elimination technique to prove that the iterated GHZ problem requires $\Omega(\Delta)$ rounds for classical algorithms. This is the first work that shows that round elimination is indeed able to separate the two models, and this also demonstrates that round elimination cannot be used to prove lower bounds for quantum-LOCAL. To apply round elimination, we introduce a new technique that allows us to discover appropriate problem relaxations in a mechanical way; it turns out that this new technique extends beyond the scope of the iterated GHZ problem and can be used to e.g. reproduce prior results on maximal matchings [FOCS 2019, PODC 2020] in a systematic manner. (10.1145/3717823.3718233)
  DOI : 10.1145/3717823.3718233
• Online Locality Meets Distributed Quantum Computing
  
  • Akbari Amirreza
  • Coiteux-Roy Xavier
  • d'Amore Francesco
  • Le Gall François
  • Lievonen Henrik
  • Melnyk Darya
  • Modanese Augusto
  • Pai Shreyas
  • Renou Marc-Olivier
  • Rozhoň Václav
  • Suomela Jukka
  , 2025, pp.1295-1306. We connect three distinct lines of research that have recently explored extensions of the classical LOCAL model of distributed computing: A. distributed quantum computing and non-signaling distributions [e.g. STOC 2024], B. finitely-dependent processes [e.g. Forum Math. Pi 2016], and C. locality in online graph algorithms and dynamic graph algorithms [e.g. ICALP 2023]. We prove new results on the capabilities and limitations of all of these models of computing, for locally checkable labeling problems (LCLs). We show that all these settings can be sandwiched between the classical LOCAL model and what we call the randomized online-LOCAL model. Our work implies limitations on the quantum advantage in the distributed setting, and we also exhibit a new barrier for proving tighter bounds. Our main technical results are these: 1. All LCL problems solvable with locality $O(\log^\star n)$ in the classical deterministic LOCAL model admit a finitely-dependent distribution with locality $O(1)$. This answers an open question by Holroyd [2024], and also presents a new barrier for proving bounds on distributed quantum advantage using causality-based arguments. 2. In rooted trees, if we can solve an LCL problem with locality $o(\log \log \log n)$ in the randomized online-LOCAL model (or any of the weaker models, such as quantum-LOCAL), we can solve it with locality $O(\log^\star n)$ in the classical deterministic LOCAL model. One of many implications is that in rooted trees, $O(\log^\star n)$ locality in quantum-LOCAL is not stronger than $O(\log^\star n)$ locality in classical LOCAL. (10.1145/3717823.3718211)
  DOI : 10.1145/3717823.3718211
• A complex logistic equation for universal energy evolution in hadronic elastic scattering
  
  • Kohara Anderson Kendi
  , 2025. We introduce a universal evolution equation for elastic scattering of hadrons, derived from Regge field theory (RFT) and solved in closed analytical form. The equation emerges from a complex logistic structure and evolves initial amplitude profiles taken from existing models at fixed energy, reproducing both the differential cross sections and the integrated quantities in a broad energy range. We prove that it admits a unique solution for each initial condition and rigorously satisfies unitarity, the Froissart-Martin bound, and dispersion relations. The dynamics are governed by two physically meaningful parameters: the effective Pomeron mass $\epsilon_{\mathcal{P}}$ and the nonlinear coupling $\lambda$, both fitted at a single energy. Our approach offers a minimal, yet predictive framework for saturation and unitarization in elastic scattering and may provide a useful bridge toward small-$x$ QCD evolution.
• Information-theoretic constraints in quantum gravity and cosmology
  
  • Franken Victor
  , 2025. Perhaps the greatest success of the holographic principle is its explicit realization in Anti-de Sitter (AdS) spacetime, whose quantum description is equivalent to a conformal field theory (CFT) defined on its boundary. Despite the success of AdS/CFT, an analogous holographic description of expanding spacetimes, such as our own, remains elusive. Fundamental difficulties arise from the closed spatial topology of de Sitter (dS) spacetime. Resolving this problem would be a crucial step towards a deeper understanding of the early history of our universe.In parallel, key progress has been made through the discovery of the connection between quantum information and the geometry of spacetime. Stemming from black hole thermodynamics, this idea has shed light on fundamental problems in the description of black holes and the AdS/CFT correspondence. Remarkably, quantum information appears to be a natural language for describing quantum effects in gravity that extend beyond the framework of AdS/CFT and black holes. In this thesis, we present new results on quantum information constraints in gravity that are of interest to cosmological models and demonstrate how this approach sheds light on cosmological holography.A remarkable example of this framework is Bousso's conjecture that the number of degrees of freedom necessary for the description of a spatial region is bounded by the area of its boundary divided by 4Ghbar with G being Newton's constant. As the Bousso bound can be violated by quantum effects, it has been proposed that one should replace ext{Area}/4Ghbar by the generalized entropy S_{m gen}= ext{Area}/4Ghbar + S_{m out} where S_{m out} is the entropy of quantum fields outside the spatial region, leading to a quantum Bousso bound. Another crucial conjecture is quantum focusing, which generalizes the classical property that light must focus in the presence of matter. It can be related to the quantum Bousso bound and forbids the existence of pathological spacetimes. We show that Jackiw-Teitelboim gravity — a toy model of quantum gravity that provides a controlled setting for exploring quantum gravitational effects — can be used to study the validity of these conjectures. In particular, we prove the quantum Bousso bound in this framework. We also prove a weakened version of quantum focusing that is sufficient for all of its applications. Interestingly, we find violations of the unrestricted formulation of quantum focusing in this model.A crucial implication of the Bousso bound is the static patch holography conjecture, where the causal region of an observer in dS space is fully described by a dual theory living on the cosmological horizon. We propose a generalization of this conjecture to a broad class of closed Friedmann-Lemaître-Robertson-Walker (FLRW) spacetimes. We introduce a covariant prescription for computing holographic entanglement entropy in this holographic framework, leading to a formulation of subregion-subregion duality. In particular, we argue that entangling the holographic theories associated with complementary observers gives rise to the emergence of the inflationary region in de Sitter space. The FLRW generalization provides a cosmological and time-dependent realization of the idea that entanglement constructs spacetime.Finally, we discuss the Connected Wedge Theorem, which establishes a relation between the causal structure of spacetime and information-theoretic constraints in the holographic dual. The gravitational counterpart of this statement derives from quantum focusing. We argue that maintaining the consistency of static patch holography with this theorem leads to constraints on the causal structure of the dual theory. Our results suggest a novel relation between static patch holography and the dS/CFT correspondence, an alternative approach to cosmological holography. (10.70675/569c65ebz3171z45c4z8bf4zdb70be128c50)
  DOI : 10.70675/569c65ebz3171z45c4z8bf4zdb70be128c50