Interested in a PhD at LPTMS ?

LPTMS Internship Proposal: Self-assembly in space and time

Contact: Martin Lenz

Recent experimental developments have made assembling machines at the nanometer scales that mimic or even attempt to surpass the functions of biological objects an increasingly reasonable goal (see https://www.nobelprize.org/prizes/chemistry/2016/summary/). Despite remarkable progress in manufacturing individual nanometer-sized objects with controlled shapes however (see an example in the illustration), assembling many of them into larger structures remains an open challenge and an active field of research.
In this project we will undertake an additional challenge, namely to self-assemble such objects not only in space, but also in time. Specifically, we will explore the design principles for DNA origami
particles produced by our collaborator Seth Fraden (Brandeis University, USA) to assemble over a given sequence over time, which will allow for an actin-like treadmilling (coordinated polymerization from one end, depolymerization from the other) of a polymer-like structure under e.g., temperature cycling. Such mechanisms could be key in controlling the motor action of prospective molecular machines.
In a second stage (e.g., during a PhD), the intern may develop simulations tools to optimize particle shapes for self-assembly of printed particles produced at PMMH in collaboration with Julien Heuvingh and Olivia du Roure. The successful applicant will have a taste for numerical simulations and working with experimentalists.

Lenz_Internship&Thesis


LPTMS PhD proposal : Localization in open quantum systems

Contacts: Alberto Rosso (LPTMS) and Laura Foini (IphT)

Understanding how a many-body quantum system thermalises and when, at the opposite, it keeps memory of the initial preparation is an extraordinary challenge which has attracted enormous attention.
Nowadays, most of the efforts focus on closed systems where the competition between disorder and interactions leads either to thermalization or many body localisation (MBL). In this context the presence of an external bath is believed to induce always thermalisation and destroy any fingerprint of localisation. This is in general not true. The goal of this project (an internship that can lead to a thesis) is to study localisation effects in open systems (e.g. in interaction with a thermal bath and eventually a drive). Two directions will be investigated:
▪ The quench of a many-body system prepared in a state out-of equilibrium and let evolve in a bath of harmonic oscillators
▪ The stationary state of a system in contact with a thermal bath and driven out of equilibrium by irradiation.
In the first case we will focus on non-perturbative effects induced by the strong coupling with the bath.
In the second example we are interested in the nature of the stationary state using a weak coupling Lindblad approach. The work is both numerical and analytical and has strong connections with NMR experiments.


LPTMS Internship Proposal: Localization in open quantum systems

Contacts: Alberto Rosso (LPTMS) and Laura Foini (IphT)

Understanding how a many-body quantum system thermalises and when, at the opposite, it keeps memory of the initial preparation is an extraordinary challenge which has attracted enormous attention.
Nowadays, most of the efforts focus on closed systems where the competition between disorder and interactions leads either to thermalization or many body localisation (MBL). In this context the presence of an external bath is believed to induce always thermalisation and destroy any fingerprint of localisation. This is in general not true. The goal of this project (an internship that can lead to a thesis) is to study localisation effects in open systems (e.g. in interaction with a thermal bath and eventually a drive). Two directions will be investigated:
▪ The quench of a many-body system prepared in a state out-of equilibrium and let evolve in a bath of harmonic oscillators
▪ The stationary state of a system in contact with a thermal bath and driven out of equilibrium by irradiation.
In the first case we will focus on non-perturbative effects induced by the strong coupling with the bath.
In the second example we are interested in the nature of the stationary state using a weak coupling Lindblad approach. The work is both numerical and analytical and has strong connections with NMR experiments.


LPTMS postdoc: Postdoctoral position on the physics of amorphous solids and glasses

Missions : Un poste post-doctoral est ouvert au LPTMS Orsay sur la physique des solides et des verres amorphes dans le cadre de la collaboration Simons "Cracking the glass problem".
Une description détaillée de la collaboration est disponible sur le site : https://scglass.uchicago.edu/

A Post-doctoral position is open at LPTMS Orsay on the physics of amorphous solids and glasses within the context of the Simons collaboration "Cracking the glass problem".
A detailed description of the collaboration can be found on the site: https://scglass.uchicago.edu/

Activités : Le post-doctorant effectuera des recherches théoriques et numériques en collaboration avec Silvio Franz et d'autres chercheurs de la région parisienne et au-delà.
• Les sujets:
1. Mécanique statistique des systèmes désordonnés: verres, verres de spin, systèmes désordonnés élastiques, modèles élasto-plastiques, etc.
2. Applications de la physique statistique à d'autres disciplines (informatique, inférence et statistique, biologie)

The post-doc will perform theoretical and numerical research in collaboration with Silvio Franz and other researchers in the Paris area and beyond.
• Topics:
1. Statistical mechanics of disordered systems: glasses, spin glasses, elastic disordered systems, elasto-plastic models, etc.
2. Applications of statistical physics to other disciplines (computer science, inference and statistics, biology)

Compétences : Le candidat aura une expérience de la recherche en physique statistique, systèmes désordonnés et vitreux, applications interdisciplinaires de la physique statistique

The candidate will have experience in research in Statistical Physics, disordered and glassy systems, interdisciplinary applications of statistical physics.

Contexte de travail : Les travaux seront conduits au LPTMS, laboratoire commun du CNRS et de l'Université Paris-Sud à l'atmosphère résolument internationale. Situé à Orsay, il se trouve à environ 30 minutes du centre de Paris par transport en commun (RER). Une présentation détaillée des activités du laboratoire est disponible sur le site http://lptms.u-psud.fr/fr

The work is to be conducted at LPTMS, a joint laboratory of CNRS and Université Paris-Sud with a markedly international atmosphere. Located in Orsay, it is about 30 minutes away from central Paris via a frequent, direct commuter train.

Contact: Silvio Franz


LPTMS postdoc: Postdoctoral position in theoretical physics

Missions :

Le poste est financé avec les moyens du Conseil Européen de la Recherche dans le cadre du projet LoCoMacro (Local Control of Macroscopic Properties in Isolated Many-body Quantum Systems), présenté par Maurizio FAGOTTI à la session 2018 du ERC Starting Grants. Ce projet de recherche porte sur l'étude des effets d'inhomogénéités sur les systèmes hors d'équilibre après une soi-disante trempe quantique globale. C'est-à-dire l'évolution temporelle hors-équilibre d'états avec une énergie significativement plus élévée que l'état fondamental, pour lesquelles, généralement, une description statistique devient appropriée. Une particularité de LoCoMacro est l'intérêt porté aux effets globaux d'inhomogénéités qui se trouvent seulement dans une petite partie du système. Le projet s'intéresse à la fois aux modèles exactement solubles qu'on examinera avec des méthodes analytiques, qu'aux systèmes génériques lesquelles sont plus facilement abordés avec des méthodes numériques. Le groupe de recherche sera composé de chercheurs aux capacités hétérogènes et l'échange des savoirs et découvertes sera donc un aspect clé de son activité.

Activités :

Le postdoc contribuera à l'étude numérique et analytique de l'évolution temporelle des systèmes quantiques à plusieurs corps à basse dimension en présence d'inhomogénéités.

Compétences :

Les candidats doivent posséder un doctorat en physique. D'autres critères essentiels à ce poste sont l'intérêt pour la dynamique hors équilibre et la maîtrise des méthodes numériques pour étudier l'évolution du temps dans les systèmes quantiques à plusieurs corps à basse dimension (en particulier les techniques de réseaux de tenseurs); le candidat idéal est un chercheur indépendant qui souhaite améliorer les méthodes existantes et éventuellement développer de nouvelles techniques pour attaquer efficacement les problèmes hors équilibre sans invariance translationnelle.
Une bonne maitrise de l'anglais parlé et écrit est requise.

Contexte de travail :

Le candidat retenu travaillera sous la supervision de Dr Maurizio FAGOTTI et bénéficiera de l'environnement de recherche stimulant du Laboratoire de Physique Théorique et Modèles Statistiques (LPTMS).
Le Laboratoire (créé en 1998) est une Unité Mixte de Recherche CNRS - Université Paris-Sud et héberge une cinquantaine de chercheurs. Les thématiques sont centrées autour de la physique statistique à la fois dans ses applications au cœur de la physique mais aussi dans ses ouvertures vers d'autres disciplines.
Etant une unité de recherche commune entre le CNRS et l'Université Paris-Sud, le laboratoire a accès à des installations informatiques telles que le «mésocentre informatique» Paris-Sud et, pour les calculs à grande échelle, aux installations nationales telles que IDRIS.

Informations complémentaires :

Le salaire suivra les règles standard du CNRS et dépendra de l'expérience. En plus du salaire, un généreux fond pour les voyages est prévu. Le candidat retenu devrait prendre ses fonctions au cours de 2019; la date précise sera fixée d'un commun accord.
Les candidatures devront obligatoirement comporter:
- un curriculum vitae et les coordonnées d'au moins deux personnes susceptibles de donner un avis motivé sur le candidat; dans le même document, fournir une liste des publications comprenant une sélection de deux ou trois publications pour lesquelles l'importance du travail est discutée et la contribution du candidat est soulignée;
- une lettre concise de motivation décrivant l'intérêt du candidat pour le projet de recherche.
Toute candidature incomplète ne sera pas examinée.

Date limite de réception des candidatures: 14/04/2019.

All applications must transit via the CNRS portal : 

https://emploi.cnrs.fr/Offres/CDD/UMR8626-MAUFAG-003/Default.aspx


LPTMS PhD Proposal: inhomogeneous systems out of equilibrium

Responsable: Maurizio FAGOTTI + 33 (0)1 69 15 32 64

A fundamental concept in statistical physics is that the equilibrium properties of systems with a huge number of degrees of freedom can be described by few parameters, first and foremost the temperature. The latter can be tuned to modify the physical properties, and even the forms in which matter manifests itself, so-called phases of matter (e.g. solid, liquid, etc.). This generally requires a global control of the system, but there are also situations in which a local perturbation is sufficient to induce a phase transition. For example, pure water can be supercooled below its normal freezing point, remaining liquid; it is then sufficient to put the liquid in contact with a small piece of ice to induce global freezing.

When the system is not at equilibrium, its description becomes more complicated; nevertheless, a statistical description was shown to emerge when a quantum many-body system, isolated from the rest, is left to evolve for a long time. Being isolated, the system can not relax to an equilibrium state, but, when scrutinised locally, it appears as if it were prepared at an effective temperature or in some exotic state of matter. Arguably, the best understood situation is a quantum quench of a global parameter in a translationally invariant quantum many-body system.

In this thesis we will go beyond the assumption of translational invariance, studying the effects of inhomogeneities on the nonequilibrium dynamics after quantum quenches.

To apply, please refer to http://lptms.u-psud.fr/maurizio-fagotti/jobs/


LPTMS PhD Proposal: Models and Time Series Analysis for Human Sports Performance

Responsable: Thorsten Emig + 33 (0)1 69 15 31 80

This project is directed to students with a strong background in quantitative methods from statistical physics, and ideally some knowledge of machine learning, computational physiology and statistical analysis of large data. Interest in sports performance would be useful. Expected are both analytical and computer programming
skills.

Models for human sports performances of various complexities and underlying principles have been proposed, often combining data from world record performances and bio-energetic facts of human physiology. For running, we were the first to derive an observed logarithmic scaling between world record running speeds and times from basic principles of metabolic power supply. We showed that various female and male record performances (world, national) and also personal best performances of individual runners for distances from 800m to the marathon are excellently described by our approach, with mean errors of (often much) less than 1%.

Main goal of this thesis project is the data-driven modeling of physiological and biomechanical processes in endurance sports, in particular running. The physiological and mechanical response of humans to exercise constitutes a complex system that involves many dynamical variables. Examples are the beat-to-beat intervals between heart beats, oxygen uptake, and stride frequency to name a few. These variables show inherent fluctuations that can be correlated.

Time series analysis can be used to detect these correlations which can show fractal scaling. This has been demonstrated for patients with cardiac diseases by Goldberger (see references below). Methods include detrended fluctuation analysis (DFA), multifractal DFA, EMD, multiscale entropy, and transfer entropy.

Models for complex physiological systems shall be constructed by learning from data. For example, running performance has been studied using recent advances in machine learning (see reference by Blythe and Kiraly). One aspect of this project is to apply machine learning to complex physiological data for endurance exercise and compare the so obtained results to findings from other methods.

This project potentially involves collaborations with Prof. A. Goldberger (Harvard Medical School) and Prof. E. Räsänen (TUT, Finland).

The official application can be found on the web site of Ecole Doctorale at https://www.edpif.org/fr/recrutement/prop.php

You can also contact me directly at thorsten.emig@u-psud.fr or at 01.69.15.31.80.

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LPTMS PhD Proposal: Mean field games

Responsable: Denis ULLMO + 33 (0)1 69 15 74 76

Mean field games present a new area of research at the boundary between applied mathematics,‭ ‬social sciences,‭ ‬engineering sciences and physics.‭ ‬It has been initiated a decade ago by Pierre-Louis Lions‭ (‬recipient of the‭ ‬94‭ ‬Fields medal‭) ‬and Jean-Michel Lasry as a new and promising tool to study many problem of social sciences,‭ ‬and with an explicit mention of the influence of concepts coming from physics‭ (‬the notion of‭ “‬mean field approximation‭”)‬.‭ ‬This field has since then grown significantly,‭ ‬and after a period where mainly stylized models where introduced,‭ ‬we witness now the appearance of‭ (‬necessarily more involved‭) ‬mean field game models closer to practical applications in finance,‭ ‬vaccination policies,‭ ‬or energy management through smart electronics.

Up to now,‭ ‬the development of Mean Field Games has mainly originated from the mathematics and economic communities.‭ ‬Mean Field Games theory is,‭ ‬however,‭ ‬by essence a multi-disciplinary field for which the input of physicists is much needed.‭ ‬Indeed,‭ ‬as important as they are,‭ ‬the studies of internal consistency and the numerical schemes developed by mathematicians cannot replace the deeper
understanding of the behavior of these models,‭ ‬obtained in particular through powerful approximation schemes,‭ ‬that physicists‭ (‬and essentially only them‭) ‬know how to provide.

For physicists a good‭ “‬entry point‭” ‬to the problematic of Mean Field Games is through the formal,‭ ‬but deep,‭ ‬connection between Mean Field Games and the nonlinear Schroedinger‭ (‬or Gross-Pitaevskii‭) ‬equation.‭ ‬This connection makes it possible to import to the field of Mean Field Games a variety of tools‭ (‬ranging from exact methods and approximation schemes to intuitive qualitative descriptions‭) ‬which have been developed along the year by physicists when studying interacting bosons or gravity waves in inviscid fluids.

The general subject of the proposed thesis is the study of Mean Field Games from a physicist point of view,‭ ‬that is with an objective to provide a true understanding‭ (‬through the identification of the relevant parameters and scale and the development of approximation schemes in the regimes of interest‭) ‬of the solutions of Mean Field Games equations.‭ ‬More specifically,‭ ‬two possible directions the proposed PhD ‬could take would be:

1.‭ ‬The study of phase transition in Mean Filed games.

2.‭ ‬To use the knowledge obtained‭ ‬on simple models to study more complicated Mean Field Games,‭ ‬and in particular address more realistic‭ (‬less stylized‭) ‬Mean Field Games.

These studies should imply a mix between analytical and numerical works,‭ ‬somewhat more shifted on the analytical side.


LPTMS Internship Proposal: Searching for topological physics in dissipative Ytterbium gases

Dissipation is ubiquitous in experiments on quantum matter and it typically reduces the timescales
over which pristine quantum phenomena can be investigated or lowers the quality of the
measurements. It’s an “enemy” that has to be fought harshly and roughly. In this internship we
will change the paradigm and consider dissipation as a resource. Dissipation can induce genuine
and interesting quantum effects (see for instance Ref. 1) and we are interesting in proposing
realistic experiments that can reveal them.

We will focus on the experiments on ultracold ytterbium gases that are currently realized in
several laboratories around the world, among which those at Collège de France in Paris (see
Ref. 2). The goal of this internship is to characterize theoretically the interplay between (i) the
dissipative mechanisms that distinguish these atoms and (ii) the unavoidable presence of atomatom
interactions (Ref. 3 presents some first data obtained in Hamburg, Germany). We will
inspect whether the dissipation-induced topological properties presented in the model of
reference 4, where interactions are neglected, can be observed in Ytterbium gases, where
interactions cannot be neglected. The main investigation tool will be advanced numerical
algorithms based on matrix-product states, that allow for the study of dissipative many-body
systems (see Ref. 5 for an article where such methods have been used to characterize dissipative
topological models).

References:
1. F. Verstraete, M. W. Wolf and J. I. Cirac, Nature Physics 5, 633 (2009).
2. R Bouganne et al., New J. Phys. 19, 113006 (2017).
3. K. Sponselee et al., arXiv:1805.11853 (2018).
4. M. S. Rudner and L. S. Levitov, Phys. Rev. Lett. 102, 065703 (2009).
5. F. Iemini, D. Rossini, R. Fazio, S. Diehl and L. Mazza, Phys. Rev. B 93, 115113 (2016)

Director:
Leonardo MAZZA
leonardo.mazza@u-psud.fr
https://sites.google.com/site/leonardmaz/

pdfDissipativeYtterbium


LPTMS PhD Proposal: Exclusion statistics and lattice random walks

Responsable: OUVRY Stéphane + 33 (0)1 69 15 36 30

Thesis proposal :Recently [1] a formula for the algebraic area enumeration of closed random walks on a square lattice has been obtained from the Kreft coefficients which encode the Schrodinger equation of the quantum Hofstadter model.

The Hofstadter model (a charged particle hopping on a square lattice coupled to a perpendicular magnetic field) has a spectrum which is a rare example of a quantum fractal. It happens to be related to closed random walks on a square lattice via a mapping between the n-th moment of the Hofstadter Hamiltonian and the generating function for the enumeration of close lattice walks making n steps and enclosing a given algebraic area. More recently [2] the algebraic area enumeration was generalized to a wider class of random walks and lattices by recognizing the underlying role of exclusion statistics in the enumeration. Several key observations both in [1] and [2] happen to be still incompletely understood and not yet seated on solid mathematical grounds. The enumeration itself has a complexity which increases exponentially with n making it difficult to be used for walks with a large number of steps. The thesis will focus on a better understanding and improving of [1] and [2], in particular simplifying the formula to make it more tractable for large n. Also the investigation of various lattices and random walks will be pushed forward.

[1] S. Ouvry and S. Wu, «The algebraic area of closed lattice random walks » arXiv:1810.04098
[2] S. Ouvry and A. Polychronakos, «Exclusion statistics and lattice random walks » arXiv:1908.00990