Accueil du site > À la une
À la une
Prix de thèse
Denis Rochette a reçu le prix de l’Académie des sciences, des inscriptions et des belles lettres de Toulouse pour sa thèse “Asymmetric cloning in quantum information theory” réalisée sous la co-direction Ion Nechita (LPT) et de Clément Pellegrini (IMT).
How quantum properties control electrolyte transport in carbon nanotubes ?
In an letter published in J. Phys. Chem. Lett., T. Hennequin and M. Manghi of the LPT have theoretically studied, in collaboration with researchers of the Charles Coulomb Laboratory of Montpellier, the transport of ions in water through a CNT. CNTs are very interesting materials in condensed mattter due to their mechanical stiffness, thermal conductivity, and chemical reactivity. Their outstanding electronic properties (finite quasi-1D electronic density of states (DOS), metallic or (...)
Quantum electrodynamics in triangular magnets
Quantum electrodynamics (QED) is the fundamental theory that describes the interactions between electrons and photons. Its success has led some to wonder if quantum field theories, like QED, can describe quasiparticles in a solid. These collective excitations include phonons, which describe lattice vibrations, and magnons, which are waves in a magnetic material but might also be of a more exotic nature. In a recent collaboration, Sylvain Capponi and his colleagues have shown that QED in two (...)
Disordered Majorana fermions are insensitive to interactions in one dimension
In Phys. Rev. Lett. 132, 056502 (2024) Chepiga and Laflorencie found that in one dimension, the presence of disorder makes Majorana particles insensitive to interactions, a behavior already observed for Dirac fermions.
T lymphocytes gradually activate integrin nanoclusters to tune their cytotoxic activity
C. Lacouture et al., LFA-1 nanoclusters integrate TCR stimulation strength to tune T-cell cytotoxic activity, Nat. Commun. 15, 407 (2024)
In the context of a PhD thesis co-supervised by a biologist from Infinity and a theoretical physicist from LPT, the role played by nanoclusters of LFA-1, an integrin found in white blood cells, was investigated. The activation of LFA-1 is a key step of the immune response of cytotoxic T lymphocytes, when they come into contact with infected or cancer cells.
Subvention scientifique 2023 de la fondation Simone et Cino del Duca
Fabien Alet, Directeur de Recherche au CNRS et directeur-adjoint du LPT, fait partie des trois Lauréats 2023 des Subventions scientifiques de la fondation Simone et Cino del Duca. L’Académie des Sciences lui a rendu hommage à l’occasion de la cérémonie de remise des prix sous la Coupole de l’Institut de France, le 17 octobre 2023. Fabien Alet est un théoricien de la matière condensée, spécialiste du problème à N corps quantique et des transitions de phases non-conventionnelles. La subvention vient (...)
Coopération et tromperie dans les groupes humains via des interactions stigmergiques
Dans un article publié dans PNAS, des scientifiques du LPT, du CRCA et de la TSE présentent les résultats et la modélisation d’une expérience imitant les systèmes de recommandation par étoiles des services et commerces sur le web.
États liés Skyrmion-électron dans un antiferromagnétique de Néel
Les textures topologiques telles que les Skyrmions et les parois de domaine ont attiré beaucoup d’attention grâce à leur beauté, leur intérêt fondamental, et au rôle qui leur est promis dans le cadre du traitement de l’information. Dans un article paru dans la Collection spéciale en l’honneur d’Emmanuel Rashba, deux physiciens du LPT ont démontré qu’un Skyrmion dans un aimant antiferromagnétique de Néel lie des électrons en produisant des états localisés. En présence d’électrons dopants, cela transforme le (...)
A complex network approach to harmonic structures in Beethoven quartets
Researchers from LPT and LPTMS have recently proposed a complex network approach to the harmonic structure underpinning western tonal music. Using a database of Beethoven’s string quartets, they have constructed a directed network whose nodes are musical chords and edges connect chords following each other. They have studied the properties of the network, and explored its community structure and its musical interpretation. They have also proposed statistical measures stemming from network (...)
Nearly Deconfined Spinon Excitations in the Square-Lattice Spin-1/2 Heisenberg Antiferromagnet
Similar to how sound waves propagate through everyday materials, some materials can carry magnetic waves, which are collective excitations of electronic magnetic moments (or spins). These “spin waves” can be detected in neutron-scattering experiments. Theoretically, it is believed that the spin waves can sometimes split up (or fractionalize) into a different kind of excitation, called a spinon, which carries only half of the magnetic moment associated with a normal spin wave. Recent (...)
An Ideal Test Bed for 2D Magnetism
Phys. Rev. Lett. 127, 037204 (2021)
Building on large-scale simulations, we show that monolayer CrCl3 exhibits tunable magnetic anisotropy upon a compressive strain thus achieving both ferromagnetic and antiferromagnetic 2D Ising-type order as well as a BKT regime.
Preuve expérimentale du couplage spin-orbite Zeeman
Ces dernières années, un énorme effort de recherche a été entrepris pour construire des dispositifs électroniques fondamentalement nouveaux (souvent appelés "dispositifs spintroniques") qui utiliseraient le spin de l’électron au même titre que sa charge. Une part importante de cet effort s’est concentrée sur la compréhension et l’utilisation du couplage spin-orbite, responsable de l’interaction entre le spin de l’électron et son mouvement orbital. Bien que le couplage spin-orbite soit devenu depuis (...)
Chaos-assisted tunneling resonances in a synthetic Floquet superlattice
The field of quantum simulation, which aims to use one quantum system to simulate another, has grown rapidly in recent years as an alternative to the universal quantum computer. The emphasis so far has been on the use of regular systems which seem a priori easier to control. However, it has been known for the last century that many systems display varying degrees of chaos. Chaotic systems exhibit exponential sensitivity to initial conditions and typical ergodic trajectories in phase space. (...)
Propriétés vitreuses de la localisation d’Anderson
Des simulations numériques révèlent que le phénomène de localisation d’Anderson, qui se manifeste dans le transport quantique, vérifie à deux dimensions et à température nulle des propriétés fondamentales des verres : l’accrochage, les avalanches et le chaos. Ces propriétés dépendent des interférences quantiques, faisant de la localisation d’Anderson une sorte de verre quantique.
Décès de Robert Fleckinger
Notre collègue Robert Fleckinger est décédé le 2 mars 2019. Il était membre du LPT depuis sa création et en a accompagné toutes les évolutions. En retraite depuis quelques années, il continuait à venir régulièrement. Nous perdons un collègue et ami qui manquera à tous.
How salting DNA makes it more flexible !
The rigidity of double-stranded DNA plays a major role in the structuring of the chromosome and thus the expression of genes, as well as in nanotechnology where DNA is used as a building block. But, how is this rigidity influenced by the presence of different types of ions ? In this work, teams from the Institut de Pharmacologie et Biologie Structurale and the Laboratoire de Physique Théorique-IRSAMC in Toulouse responded both experimentally and theoretically to this question.
Is 1D physics experimentally accessible in real systems ?
At low temperature, critical one-dimensional (1D) quantum systems, such as spin chains, are theoretically described by the Tomonaga-Luttinger liquid (TLL) theory. In realistic quasi-1D materials, however, residual couplings are always present, and these systems may escape the theoretical 1D world to get eventually ordered at lower temperature. In order to define a genuine “1D temperature window” in quasi-1D systems for dynamical quantities such as the NMR relaxation rate or the dynamical structure factor that is probed by inelastic neutron scattering, the authors present a comprehensive theoretical study based on analytical as well as numerical approaches. They are able to describe the full temperature crossover for weakly coupled chains and, in particular, the universal 1D window where the TLL picture can be experimentally observed.
Reference : M.Dupont, S. Capponi, N. Laflorencie, and E. Orignac
Phys. Rev. B 98, 094403 (2018), selected as an editor’s suggestion.
Les poissons se la coulent douce dans un banc
Les bancs de poissons offrent un exemple fascinant de comportement collectif dans lequel le groupe se coordonne sans avoir besoin de leader. Mais quel est le rôle joué par le fluide et l’écoulement dans cette coordination ? C’est pour répondre à cette question qu’un groupe de chercheurs (dont un du LPT) a mis au point un modèle original permettant de simuler les interactions hydrodynamiques et sociales entre des centaines de poissons.
A. Filella, F. Nadal, C. Sire, E. Kanso, C. Eloy. Model of collective fish behavior with hydrodynamic interactions, Physical Review Letters 120, 198101 (2018). Cet article a reçu le label "PRL Editors’ Suggestion", est commenté dans le magazine de l’APS Physics, et fait l’objet d’un communiqué de presse national du CNRS.
Distinguer les ordinateurs des humains au jeu de go
L’intelligence artificielle est de plus en plus en mesure de se substituer au cerveau humain. Il y a plusieurs décennies, le mathématicien Alan Turing s’était déjà posé la question de reconnaître un humain d’une intelligence artificielle avancée (test de Turing). Récemment, après des années d’efforts, le programme d’ordinateur AlphaGo a été capable de battre les meilleurs joueurs de go. Trois théoriciens du LPT Toulouse et du LPTMS Orsay ont appliqué la théorie des réseaux à des bases de données de parties de go jouées par des humains et par différents programmes informatiques. Ils ont montré que la structure des réseaux issus des parties humaines et informatiques était différente, ouvrant la voie à un test de Turing pour les simulateurs de go. Ces résultats sont publiés dans la revue Europhysics Letters. Voir aussi le communiqué sur Phys.org.
Comment les poissons interagissent et coordonnent leurs déplacements dans un banc
Des chercheurs du CRCA et du LPT à Toulouse, et leurs collaborateurs chinois et britanniques ont étudié comment des poissons s’influencent mutuellement lorsqu’ils effectuent collectivement des changements spontanés de direction. Communiqué de presse de la revue PLOS Computational Biology (en anglais) qui consacre sa une à ce travail ; Actualité scientifique de l’Institut des Sciences Biologiques du CNRS
Comment développer l’intelligence collective grâce à l’information sociale
Une équipe interdisciplinaire de chercheurs impliquant un physicien et un doctorant du LPT vient de publier dans les Proceedings of the National Academy of Sciences USA les résultats d’expériences et de modélisation quantifiant comment les gens prennent en compte l’opinion des autres pour corriger leur réponse initiale dans des tâches d’estimation. Communiqué de presse nationale du CNRS
Topological chiral spin liquid groundstate of a frustrated antiferromagnetic Heisenberg model
A simple spin-12 frustrated antiferromagnetic Heisenberg model (AFHM) on the square lattice—including chiral plaquette cyclic terms—was argued to host a bosonic Kalmeyer-Laughlin (KL) fractional quantum Hall ground state. Here, we construct generic families of chiral projected entangled pair states (chiral PEPS) with low bond dimension which, upon optimization, provide better variational energies than the KL Ansatz. The optimal PEPS exhibits chiral edge modes described by the (...)
How disorder can turn into long-range order at high magnetic field ?
Building on NMR experiments at high magnetic field, physicists have demonstrated that impurity-induced disorder in a Mott insulator can lead to the revival of long-range order.
Phys. Rev. Lett. 118, 067203 (2017)
Phys. Rev. Lett. 118, 067204 (2017)
See also CNRS news INP website
Local injection of pure spin current generates electric current vortices
In a paper, published by Applied Physics Letters, Yaroslaw Bazaliy of the University of South Carolina and Revaz Ramazashvili of the LPT have studied local injection of pure spin current into an electrically disconnected ferromagnetic-normal sandwich. Curiously enough, it turns out that local spin injection inevitably induces electric current vortices, that are centered at the normal-ferromagnetic interface. This finding invites us to revisit various aspects of spin injection in spintronic devices.
Temperature dependence of the NMR relaxation rate 1/T1 for quantum spin chains
Maxime Dupont, PhD student in LPT, together with Sylvain Capponi and Nicolas Laflorencie, studied dynamical correlations at finite temperature in quantum spin chains using matrix product state techniques, thus allowing to extract the NMR relaxation rate. This work addresses the delicate question of the low-temperature dimensional crossover in realistic materials, such as coupled S=1 chains material DTN.
Physique théorique : particules sur la grille
En physique des solides, le comportement des systèmes dits fortement corrélés est un sujet d’intérêt à la fois d’un point de vue théorique et expérimental. Ces matériaux ont, en effet, des propriétés électroniques particulières : les électrons situés sur la couche périphérique sont si fortement liés à leur atome que, pour les déplacer, il faut une énergie non négligeable alors que, dans les matériaux courants, ils peuvent se déplacer presque librement. A basse température, ces systèmes fortement corrélés peuvent, (...)
Dependence of DNA Persistence Length on Ionic Strength of Solutions with Monovalent and Divalent Salts
A Joint Theory-Experiment Study : collaboration between the LPT and the IPBS and the LMGM. Using high-throughput tethered particle motion (TPM) single-molecule experiments, the double-stranded DNA persistence length, Lp, is measured in solutions with Na+ and Mg2+ ions of various ionic strengths. The data are compared to available theoretical models. No decisive theory is found which fits all the Lp values for the two ion valencies. Using high-throughput tethered particle motion (...)
Développements non perturbatifs à bases de graphes
Les techniques de perturbations basées sur un développement en graphes sont très communes en physique. Elles se heurtent à un problème générique du fait des symétries réduites des graphes : par exemple, l’absence de symétrie par translation, alors qu’elle est présente pour un système infini homogène. Une collaboration entre Sylvain Capponi et le groupe de Kai Schmidt à Dortmund a permis de dépasser cette difficulté.
Reference : K. Coester et al. 2015 EPL 110 20006 (sélectionné comme Editors’ Choice)
Many-body localization edge in the random-field Heisenberg chain
Using a massively parallel exact diagonalization technique, David Luitz, Nicolas Laflorencie and Fabien Alet have shown the existence of an extensive many-body localization edge for the random field Heisenberg chain, separating a thermal (ergodic) phase from a many-body localized (non-ergodic) regime.
Reference : Phys. Rev. B 91, 081103(R) (2015) (Editors’ Suggestion)
Real space imaging of spin polarons
Thanks to state-of-the-art NMR experiments performed in Japan on Zn doped frustrated spin compound, SrCu2(BO3)2, theorists from the LPT in collaboration with Pr. Mila in Lausanne have been able to interpret the real space profile as a magnetic polaron.
Reference : Phys. Rev. Lett. 114, 056402 (2015)
Interactions entre cultures et les personnalités les plus influentes sur Wikipédia en 24 langues - Interactions of cultures and top people of Wikipedia in 24 language editions
Deux physiciens du LPT et leurs collaborateurs ont identifié les 100 personnalités les plus influentes dans les versions en 24 langues de Wikipédia, en utilisant des outils avancés d’analyse des réseaux complexes, apportant ainsi un éclairage nouveau sur l’interaction entre cultures (English version).
Référence : PLoS ONE 10(3) : e0114825 (2015) ; Communiqué de presse CNRS
Multifractality of quantum wave functions facing perturbation
26 juin 2014
Physicists from LPT together with colleagues in Orsay, Belgium and Argentina have shown that the destruction of quantum multifractality by a perturbation can follow two different scenarios.
Reference : Phys. Rev. Lett. 112, 234101 (2014) ; Communiqué CNRS
Étude des phases prédites par un modèle de bancs de poissons déduit d’expériences - Swarming, schooling, milling : phase diagram of a data-driven fish school model
Un modèle de dynamique de bancs de poissons déduit d’expériences réalisées par le CRCA Toulouse reproduit les différentes phases usuellement observées (comme les « moulins » de la photo), et une phase rare extrêmement allongée (English version).
Référence : New J. Phys. 16, 015026 (2014) (incluant un résumé vidéo)
Spin-Wave Localization for 2D Bosons in a Random Potential
Left : Diagram Disorder - Energy of the Spin-Wave spectrum of 2D hard-core bosons in a random potential. A mobility edge separates extended from localized modes.
In Phys. Rev. Lett. 111, 160403 (2013), J.P Alvarez Zuniga and N. Laflorencie from LPT, have studied the 2D Superfluid to Bose-Glass transition using a spin-wave approach. Upon increasing the disorder strength, an insulating but gapless state emerges : the Bose-glass phase (a state absent in mean-field). Furthermore, a mobility edge in the spin-wave excitation spectrum is found at a finite frequency Ωc, decreasing with disorder, and presumably vanishing in the Bose-glass.
Gapless spin liquid in the frustrated square lattice Heisenberg quantum antiferromagnet
Left : Singlet bond weight distribution in the Liang-Doucot-Anderson picture with a linear color scale for a 8 X 8 torus.
Magnetic frustration in quantum magnets may be responsible for exotic spin liquid ground state. Using novel Tensor Network techniques we provide strong evidence that frustrating antiferromagnetic interaction stabilizes a gapless spin liquid in the Heisenberg quantum antiferromagnet on the square lattice. Such a state can be viewed as a Resonating Valence Bond (RVB) state with a distribution of singlet bonds at all distances. Our framework also enables to investigate the topological properties of this novel spin liquid.
Symmetry-protected topological phases of cold atoms in one dimension
Cartoon of two possible exotic phases for two-component alkaline-earth cold atoms with nuclear spin I=1/2 and SU(4) symmetry. These Haldane phases for nuclear spin and orbital degrees of freedom present a dilute hidder order that can be seen here as an alternation of sites with total (pseudo)spin component ±1, diluted with an arbitrary number of sites with (pseudo)spin component 0.
Fractionalization of Itinerant Anyons in One-Dimensional Chains
Left : Anyonic fusion trees for electrons, Ising σ (Majorana) anyons, and Fibonacci anyons.
The theoretical prediction of (non-abelian) Majorana particles in topological insulators and closely related systems by Kane and Mele has recently boosted the quest for the discovery of emergent non-abelian particles beyond the realm of the quantum Hall effect. Didier Poilblanc (LPT) and collaborators (Microsoft, ETH-Zurich) have constructed models of interacting itinerant non-Abelian anyons moving along one-dimensional chains.
Coulomb meets Néel
An example of a quantum wave-function, displaying at the same time antiferromagnetic and Coulomb-like dipolar behaviors, was recently evidenced.
Quantum Data Fitting
Phys. Rev. Lett. 109, 050505 (2012) ; accompanying synopsis in "Physics" by the editors of PRL
When spontaneous transmutation of particles occurs in a quantum liquid.
Phys. Rev. Lett. 109, 016403 (2012)
Phys. Rev. Lett. 109, 016403 (2012)
Comment on "Topological quantum phase transitions of attractive spinless fermions in a honeycomb lattice"
A new asymptotic theory for oscillation modes of rapidly rotating stars
Condensate-free superfluid induced by frustrated proximity effect
Ultimate quantum limits to sensitivity of nano-oscillator based "artificial noses"
In an article to appear in Europhysics Letters, a researcher from the LPT has derived the ultimate bounds of sensitivity of molecular mass measurements with nano-mechanical oscillators.
Google matrix of the world trade network
L.Ermann and D.L.Shepelyansky
Recent results obtained at LPT for new way of ranking of international world trade commerce (see here) have been highlighted at Atelier.fr launched by Antoine Sire (see here) .
Heisenberg-limited sensitivity with decoherence-enhanced measurements
Quantum-enhanced measurements use quantum mechanical effects to enhance the sensitivity of measurements. However, the required quantum states are generally highly entangled, difficult to produce, and very prone to decoherence. In work that has now appeared in Nature Communications, Daniel Braun of the LPT and John Martin (University de Liege) show how Heisenberg-limited measurements can be achieved without the use of entangled states by coupling the quantum resources to a common (...)
Quantum oscillations in antiferromagnetic conductors
Discovered in 1930, magnetic quantum oscillations were the second (after superconductivity) experimentally found macroscopic manifestation of the quantum nature of the electron : in a magnetic field, the electron energy levels in a metal become discrete, which leads to oscillations of various quantities with varying the magnetic field. For over fifty years now, magnetic quantum oscillations have been a direct and precise probe of the electron physics in metals. The scope of the (...)
Drag forces in fluctuating fields
Inclusions, or defects, moving at constant velocity through free classical fields have been shown to be subject to a drag force which depends on the field dynamics and the coupling of the inclusion to the field. The results can be used to predict the drag exerted on inclusions, such as proteins, in lipid membranes due to their interaction with height and composition fluctuations. The force, measured in Monte Carlo simulations, on a point like magnetic field moving through an Ising (...)
Ionic Capillary Evaporation in Weakly Charged Nanopores
Three members of the Statistical Physics group of the LPT have proposed in an article appearing in Physical Review Letters that a novel ionic “liquid-vapor” phase transition occurring for electrolytes in weakly charged nanopores could explain the time-dependent electrical conductivity fluctuations observed across certain biological and artificial ion channels.
Un algorithme quantique pour l’échantillonnage Monte Carlo exact
Trois chercheurs du LPT de Toulouse et du LPTMS d’Orsay ont récemment publié dans Physical Review Letters (de juin 2010) un travail où ils proposent une version quantique de l’algorithme dit de « couplage depuis le passé », proposé il y a une quinzaine d’années par James Propp et David Wilson.
Two-dimensional ranking of Wikipedia articles
A.O.Zhirov, O.V.Zhirov and D.L.Shepelyansky
Recent results obtained at LPT on two-dimensional ranking of Wikipedia articles are highlighted at Atelier.FR (see here), More information about results can be find at arxiv1006.4270 and webpage. The results of the research are submitted to Eur. Phys. J. B.
Quantifying Quantumness and the Quest for Queens of Quantum
What are the "most quantum" states that one can possibly produce and what are their properties ? Experimental progress, which has led to the coherent manipulation of a small number of quantum systems, such as trapped ions, or superconducting qubits, has rendered these questions highly relevant not only for the foundations of physics, but also for practical implementation of quantum information processing. In an article that has now appeared in the New Journal of Physics, we make the (...)
Computing fidelity at magnetic quantum phase transitions
Quantum phase transitions (QPT) play an important role in condensed matter systems. Traditional investigations of those QPT usually need the definition of an order parameter, which itself already requires a deeper understanding of the physical system. When a system undergoes a quantum phase transition, the ground-state wave-function shows a change of nature, which can be monitored using the fidelity concept.
Why DNA chains are "kinked" when observed on surfaces
DNA elastic properties on surfaces differ from ones in solution.
Atomic Force Microscopy (AFM) is widely used to observe double-stranded DNA adsorbed on surfaces. In recent experiments by Wiggins et al., « anomalies » have been detected in the distribution of bending angles along DNA (which measures its flexibility) : an over-abundance of large angles were found which are not predicted by the traditional statistical model of DNA chains, the Worm-Like Chain model (see figure). N. Destainville, M. Manghi and J. Palmeri of the statistical group of the (...)
Effective Theory of Magnetization Plateaux in the Shastry-Sutherland Lattice
The Shastry-Sutherland lattice and its realization in the material SrCu2(BO3)2 have been attracting a lot of attention due to its fascinating behavior in a magnetic field, namely that magnetization plateaux have experimentally been observed for values of 1/8, 1/4 and 1/3 of the saturation value. Because of the lack of powerful numerical techniques or unbiased analytical tools to tackle 2D frustrated systems, a promising approach consists in deriving an effective hardcore bosonic model. (...)
A gauge theory picture of an exotic transition in a dimer model
We study a phase transition in a 3D lattice gauge theory, a coarse-grained version of a classical dimer model. The dimer model on a cubic lattice, first studied by F. Alet and collaborators, displays a continuous transition between an ordered columnar phase at low temperature and a disordered phase at high temperature where dimer-dimer correlations show an algebraic decay. This is rather unusual as the standard Ginzburg-Landau theory of phase transitions generally predicts an exponential (...)
The Pairing Glue in High-Temperature Superconductors
Didier Poilblanc
The question of whether one should speak of a “pairing glue” in the Hubbard and t-J models is basically a question about the dynamics of the pairing interaction. If the dynamics of the pairing interaction arises from virtual states, whose energies correspond to the Mott gap, and give rise to the exchange coupling J, the interaction is instantaneous on the relative time scales of interest. In this case, while one might speak of an “instantaneous glue,” this interaction differs from the (...)
What is the true statistics of holons ?
Didier Poilblanc
The exact nature of holons, the charged spinless excitations of the (doped) celebrated RVB state, has been debated over the last two decades. In particular, their statistics (do they behave as fermions or bosons ?) was still controversial. A doped two-dimensional quantum dimer model describing a doped Mott insulator and retaining the original Fermi statistics of the electrons is defined and analyzed by numerical studies on small clusters. This model shows a rich phase diagram including a d-wave hole-pair unconventional superconductor at small enough doping and a bosonic superfluid at large doping. The hole kinetic energy is shown to favor binding of topological defects (similar to vortices or "visons") to the bare fermionic holons turning them into bosons, in agreement with arguments based on RVB wave-functions. Results may have interesting connections with the physics of cuprates superconductors
10th Anniversary Highlight Article in New Journal of Physics
D. Braun
Decoherence is the main concern in experimental realizations of quantum computers. In order to control the quantum computer, a certain amount of interaction with its environment is needed that destroys in general the phase coherence of the computer very quickly. An article in NJP, which was now selected as one of the 10th Anniversary Highlights articles by the editors of the journal, explains how this dilemma can in principle be avoided.
Generic mixed columnar-plaquette phases in Rokhsar-Kivelson models
Arnaud Ralko, Didier Poilblanc and Roderich Moessner
Two members of the strongly correlated system group (A. Ralko and D. Poilblanc), in collaboration with R. Moessner from MPI-PKS (Dresden), revisit the phase diagram of Rokhsar-Kivelson models, which are used in fields such as superconductivity, frustrated magnetism, cold bosons, and the physics of Josephson junction arrays. From an extended height effective theory, we show that one of two simple generic phase diagrams contains a mixed phase that interpolates continuously between columnar and plaquette states.
Spin gap and string order parameter in the ferromagnetic Spiral Staircase Heisenberg Ladder
Low-dimensional quantum magnets are fascinating objects from both experimental and theoretical points of view. This work deals with the case of weakly ferromagnetically coupled inequivalent chains and reveals the emergence of a new energy scale that is interpreted in terms of a Suhl-Nakamura interaction.
Phase separation and flux quantization in the doped quantum dimer model on the square and triangular lattices
Arnaud Ralko, Frédéric Mila and Didier Poilblanc
Two members of the strongly correlated system group (A. Ralko and D. Poilblanc), in collaboration with F. Mila from EPF Lausanne, have studied the doped quantum dimer model, a simplified model that is expected to capture the essence of hole motion in an antiferromagnet. The physics of hole motion in an antiferromagnet is of broad interest and of very high relevance for illuminating high-Tc superconductivity and quantum spin liquids in general. In this work, superfluidity, phase separation and flux quantization are discussed, giving new insights on the physics of doped Mott insulators.
DNA bubbles and bending : how conformational fluctuations modify its thermal denaturation
Three members of the statistical physics group have studied theoretically thermal DNA denaturation by illuminating the role of statistical non-uniform bending inside a DNA chain.
Entanglement-screening by nonlinear resonances
A member of the Laboratory, in collaboration with researchers from Australia, United States and Germany, has recently shown that nonlinear resonances in a classically mixed phase space allow to define generic, strongly entangled multi-partite quantum states. The robustness of their multipartite entanglement was shown to increase with the particle number, i.e. in the semiclassical limit, for those classes of diffusive noise which assist the quantum-classical transition.
Predicting the maximum or the minimum of a random signal
What is the probability that a stock prize does not fall below a certain level ? What is the probability that the total magnetization of a spin system does not change sign ? Predicting the maximum or the minimum of a random temporal signal is a challenging problem recently addressed by a member of the laboratory, which commonly appears in physics, biology, finance, and image or data processing.
Exceeding the Pauli limit
Superconducting doped spin ladders under a magnetic field parallel to their plane reveal interesting novel phases and phenomena, as recently shown by members of the Laboratory, including irrational magnetization plateaus and exceeding of the Pauli limit.
An unconventional phase transition
Phase transitions occupy a central role in physics, due both to their experimental ubiquity and their fundamental conceptual importance. The explanation of universality at phase transitions was the great success of the theory formulated by Ginzburg and Landau, and extended through the renormalization group by Wilson. However, recent theoretical suggestions have challenged this point of view.
Measuring the size of Schrödinger’s cat
Imagine you are supposed to keep the memory in your computer with its millions of bytes in a quantum superposition of two very different contents, such as the memory full of zeros and the memory full of ones. For how long you can you do this in principle, if at all ?
How to reproduce bacterial propulsion in a biomimetic way ?
By coupling the elastic properties of a rotative semi-flexible nanorod and hydrodynamic interactions, which are the source of propulsion in Stokes flows, a member of the Laboratory, in collaboration with German researchers, has shown theoretically that bacterial propulsion can be reproduced in a biomimetic way. Moreover, this work sheds light on the major role played by elasticity in flagellar motion of bacteria as E. coli.
An argentinian-french collaboration : a novel mechanism for fractional magnetization plateaus !
A novel (quite general) mechanism for the appearance of magnetization plateaus in quasi-one-dimensional quantum spin systems is proposed where the coupling to the underlying lattice plays an essential role.