64 research outputs found
Treebanking in the world of Thucydides. Linguistic annotation for the Hellespont Project
No full textThe Hellespont project (DAI, Tufts University) aims to structure the text of a passage from the ancient Greek historian Thucydides (1.89-118), in order to highlight events, persons and peoples that populate the world of the author and connect the different digital sources available for their study. Event annotation in the text in particular requires an in-depth linguistic analysis of morphology, syntax and semantics. However, the available resources for Ancient Greek do not provide adequate standards to support the encoding of semantic and pragmatic phenomena in Ancient Greek texts. In this paper, we discuss the motivation of the project and how we adapted the so called tectogrammatical annotation of the Prague Dependency Treebank to identify the events and describe their structure. The linguistic notion of valency, which is central to tectogrammatical sentence representation, proves very useful for this analysis of Ancient Greek
Generalized Hardcore Dimer Models approach to low-energy Heisenberg frustrated antiferromagnets: general properties and application to the kagome antiferromagnet
No full text26 pages, 4 figures, EPAPS inlined, manuscript revised, corrected minor typos (notably figure 2).International audienceWe propose a general non-perturbative scheme that quantitatively maps the low-energy sector of spin-1/2 frustrated Heisenberg antiferromagnets to effective Generalized Quantum Dimer Models. We develop the formal lattice independent frame and establish some important results on (i) the locality of the generated Hamiltonians (ii) how full resummations can be performed in this renormalization scheme. The method is then applied to the much debated kagome antiferromagnet for which a fully resummed effective Hamiltonian - shown to capture the essential properties and provide deep insights on the microscopic model [D. Poilblanc, M. Mambrini and D. Schwandt, arXiv:0912.0724] - is derived
Erratum: Patients with Severe Obesity during the COVID- 19 Pandemic: How to Maintain an Adequate Multidisciplinary Nutritional Rehabilitation Program? (Obes Facts. (2021) DOI: 10.1159/000513283)
No full textIn the article by De Amicis et al. entitled "Patients with Severe Obesity during the COVID- 19 Pandemic: How to Maintain an Adequate Multidisciplinary Nutritional Rehabilitation Program?" [Obes Facts. 2021, DOI: 10.1159/000513283], the author list is incorrect. The correct author list is: De Amicis R. Cancello R. Capodaglio P. Gobbi M. Brunani A. Gilardini L. Castelnuovo G. Molinari E. Barbieri V. Mambrini S.P. Battezzati A. Bertoli S
Will a Parser Overtake Achilles? First experiments on parsing the Ancient Greek Dependency Treebank
No full textWe present a number of experiments on parsing the Ancient Greek Dependency
Treebank (AGDT), i.e. the largest syntactically annotated corpus of
Ancient Greek currently available (350k words ca). Although the AGDT is
rather unbalanced and far from being representative of all genres and periods
of Ancient Greek, no attempt has been made so far to perform automatic
dependency parsing of Ancient Greek texts. By testing and evaluating one
probabilistic dependency parser (MaltParser), we focus on how to improve
the parsing accuracy and how to customize a feature model that fits the distinctive
properties of Ancient Greek syntax. Also, we prove the impact of
genre and author diversity on parsing performances
Hard-core dimer aspects of the SU(2) singlet wave function
No full text5 pages, 2 figuresInternational audienceWe demonstrate that any SU(2) singlet wave function can be characterized by a set of valence bond occupation numbers, testing dimer presence-vacancy on pairs of sites. This genuine quantum property of singlet states (i) shows that SU(2) singlets share some of the intuitive features of hard-core quantum dimers, (ii) gives rigorous basis for interesting albeit apparently ill-defined quantities introduced recently in the context of quantum magnetism or quantum information to measure, respectively, spin correlations and bipartite entanglement, and (iii) suggests a scheme to define consistently a wide family of quantities analogous to high order spin correlation. This result is demonstrated in the framework of a general functional mapping between the Hilbert space generated by an arbitrary number of spins and a set of algebraic functions found to be an efficient analytical tool for the description of quantum spins or qubits systems
Etude des excitations de basse énergie dans des systèmes magnétiques frustrés de basse dimensionnalité: gap de spin et singulets de basse énergie
No full textMembres du jury: Benoit Doucot (Rapporteur), Claudine Lacroix (Rapporteur), Claire Lhuillier (Examinateur), Philippe Mendels (Examinateur), Frédéric Mila (Directeur de thèse), Patrice Millet (Examinateur), Erik Sorensen (Président du jury)Low energy physics of the two-dimensional spin-1/2 Heisenberg antiferromagnet display a wide range of behaviours. Most of them are only partially understood especially in the case of frustrated magnets. These models not only raise theoretical questions, but are also relevant to describing physical properties of many recently synthesized compounds. In this thesis, both aspects --- theory and relation to experiments --- are analysed. Theoretically, we use a numerical approach to study the Heisenberg model on the kagomé lattice, one of the most frustrated lattices. We show that strong signatures of frustration in this model (spin gap and exponential proliferation of singlets inside the gap) can be faithfully described in terms of short range RVB states (>). Such states also provide a relatively simple picture of the low energy physics of the model. Even if the unusual properties of the kagomé antiferromagnet spectrum are believed to be the consequences of the strong frustration of this model, no other similar system was known to exhibit such a behaviour. In fact, we show exactly that these properties (spin gap filled with low lying singlets) indeed occur in a one-dimensional model of coupled tetrahedra. Lastly, we consider connections between experimental aspects of frustration and numerical studies of frustrated models. For the vanadate compound CaV4O9 --- which is the first half-filled two-dimensional system with a spin gap --- we show that the analysis of the symmetry of the first excited state, obtained by neutron scattering experiments, provides strong constraints on the parameters of the model and emphasizes the role of frustration. For Li2VO(Si,Ge)O4, susceptibility measurements compared to exact diagonalisation results allow us to identify this compound as the prototype of the J_1 - J_2 model on the square lattice and to give estimations of J_2/J_1.La physique de basse énergie du modèle de Heisenberg antiferromagnétique pour des spins 1/2 en deux dimensions recèle une grande variété de comportements, pour certains mal compris, lorsque l'on est en présence de frustration. Outre l'intérêt théorique que présente l'étude de ces modèles, il se trouve qu'ils décrivent de manière satisfaisante de nombreux composés réels maintenant synthétisés. Dans cette thèse, nous abordons les deux aspects de l'étude de ces modèles. D'un point de vue théorique, nous examinons ce modèle, à l'aide de techniques numériques, sur l'un des réseaux les plus frustrés : le réseau kagomé. Nous montrons comment les très fortes signatures de la frustration (existence d'un gap de spin peuplé d'un grand nombre d'états singulets) observées dans ce modèle peuvent être correctement comprises à l'aide d'états RVB (>, Lien de Valence Résonant) à courte portée. Cette approche présente en outre l'intérêt de donner une image relativement simple de la physique de basse énergie du modèle. Bien qu'attribuées à la forte frustration de ce modèle, les propriétés du spectre du hamiltonien de Heisenberg sur le réseau kagomé n'avaient pas d'équivalent dans les systèmes analogues. Nous mettons en évidence, de manière exacte, l'existence de propriétés semblables (gap de spin et singulets de basse énergie) dans un modèle unidimensionnel de tétraèdres couplés. Nous abordons enfin les applications de l'étude numérique des modèles frustrés à l'explication de propriétés de composés réels. En effet, il est notamment possible de confronter ces résultats à des mesures de susceptibilité ou à des expériences de diffraction de neutrons. Nous examinons tout d'abord le composé CaV4O9, premier système bidimensionnel demi-rempli présentant un gap dans son spectre d'excitations. Nous montrons que l'analyse des symétries du premier état excité permet, par comparaison avec la relation de dispersion obtenue par diffraction de neutrons, de borner les paramètres du modèle, par ailleurs difficiles à évaluer par des méthodes de chimie quantique. L'analyse de la susceptibilité rend possible, dans le cas de Li2VO(Si,Ge)O4 qui est la première réalisation du modèle J_1 - J_2 sur le réseau carré, la mise en évidence de la frustration et l'évaluation de son importance dans ces deux composés
Tensor network methods for non-equilibrium dynamics of quantum spin liquids
No full textLa présence d'interactions fortes et d'intrication dans un système quantique à plusieurs corps peut conduire à plusieurs états exotiques de la matière. Les liquides Quantum Spin sont l'un de ces ensembles d'états exotiques qui ont suscité un intérêt considérable en raison de leurs propriétés intéressantes et de leurs applications technologiques possibles. Les progrès rapides des montages d'expériences sur les atomes froids, en particulier les simulateurs d'atomes de Rydberg, ont ouvert de nouvelles voies pour étudier ces liquides de spin en une et deux dimensions. Cela nécessite des techniques théoriques avancées pour étudier les propriétés de non-équilibre d'états quantiques purs isolés. Cette thèse vise à développer des algorithmes numériques pour étudier les propriétés de non-équilibre des liquides de spin sur un réseau carré suite à une trempe quantique en utilisant le cadre des réseaux de tenseurs. Une forme variationnelle de l'ansatz Projected Entangled Pair State (PEPS) est utilisée pour décrire les liquides de spin. Une nouvelle forme symétrique du groupe de renormalisation de la matrice de transfert de coin (CTMRG), l'algorithme nécessaire pour construire la matrice de densité réduite de la fonction d'onde dans la limite thermodynamique pour une fonction d'onde PEPS à valeurs complexes, est décrite. Pour étudier la dynamique de trempe, deux algorithmes appelés update simple et update complète, ainsi que les modifications nécessaires pour les adapter à l'étude des fonctions d'onde de spin liquide, sont expliqués. Les outils sont ensuite utilisés pour étudier la dynamique de non-équilibre de l'état de la liaison de valence résonnante (RVB) avec les configurations de liaison de valence du plus proche voisin (NN), un état spin-liquide connu pour présenter des corrélations dimère-dimère critiques, dans le Collecteur PEPS.The presence of strong-interactions and entanglement in a quantum many-body system can lead to several exotic states of matter. Quantum Spin liquids are one such set of exotic states that have attracted significant interest due to their interesting properties and possible technological applications. The rapid progress in cold atom experiment setups, particularly the Rydberg atom simulators, has opened up new avenues to study these spin liquids in one and two-dimensions. This calls for advanced theoretical techniques to investigate the non-equilibrium properties of isolated pure quantum states. This thesis aims to develop numerical algorithms to study the non-equilibrium properties of spin liquids on a square lattice following a quantum quench using the framework of tensor networks. A variational form of Projected Entangled Pair State (PEPS) ansatz is used to describe the spin liquids. A new symmetric form of the Corner Transfer Matrix Renormalization group (CTMRG), the algorithm necessary to construct the reduced density matrix of the wavefunction in the thermodynamic limit for a complex-valued PEPS wavefunction, is described. To study the quench dynamics, two algorithms called simple-update and full update, along with the necessary modifications to adapt them to study spin liquid wavefunctions, are explained. The tools are then used to study the non-equilibrium dynamics of the resonating valence bond (RVB) state with nearest-neighbor (NN) valence bond configurations, a spin-liquid state that is known to exhibit critical dimer-dimer correlations, within the PEPS manifold
Quantum critical phase with infinite projected entangled paired states
No full textInternational audienc
Quantum state preparation of topological chiral spin liquids via Floquet engineering
No full textInternational audienceIn condensed matter, Chiral Spin Liquids (CSL) are quantum spin analogs of electronic Fractional Quantum Hall states (in the continuum) or Fractional Chern Insulators (on the lattice). As the latter, CSL are remarquable states of matter, exhibiting topological order and chiral edge modes. Preparing CSL on quantum simulators like cold atom platforms is still an open challenge. Here we propose a simple setup on a finite cluster of spin-1/2 located at the sites of a square lattice. Using a Resonating Valence Bond (RVB) non-chiral spin liquid as initial state on which fast time-modulations of strong nearest-neighbor Heisenberg couplings are applied, following different protocols (out-of-equilibrium quench or semi-adiabatic ramping of the drive), we show the slow emergence of such a CSL phase. An effective Floquet dynamics, obtained from a high-frequency Magnus expansion of the drive Hamiltonian, provides a very accurate and simple framework fully capturing the out-of-equilibrium dynamics. An analysis of the resulting prepared states in term of Projected Entangled Pair states gives further insights on the topological nature of the chiral phase. Finally, we discuss possible applications to quantum computing
The spin gap of CaV4O9 revisited
No full textThe large-plaquette scenario of the spin gap in CaV4O9 is investigated on the basis of extensive exact diagonalizations. We confirm the existence of a large-plaquette phase in a wide range of parameters, and we show that the most recent neutron scattering data actually require an intra-plaquette second-neighbor exchange integral much larger than the inter-plaquette one, thus justifying the perturbative calculation used in the interpretation of the neutron scattering experiments
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