Laboratoire de Physique Statistique, ENS, Paris
"Recent advances on water transport in extreme confinement"
Nanofluidics is the frontier where the continuum picture of fluid mechanics confronts the atomic nature of matter. Recent experiments reported exceptional transport properties of water when confined in carbon nanopores. This has stimulated interest in carbon-based membranes for desalination, nano-filtration, and energy harvesting. But these works raised fundamental questions on the specificity of the water-carbon interface, its structure, reactivity and dynamics. There is however a lack of experimental results because, even though studies have explored transport through individual nanotubes, none has met the considerable technical challenge of unambiguously measuring the permeability of a single nanopores.
In this work, we have tackled the question of transport across individual nanotubes by developing new methods based on the manipulation of nano-scale building blocks. This allows to fabricate original fluidic and mechanical systems involving single nanotubes.
Our experiments reveal a number of unexpected behavior of water and ion transport in nanotubes. In particular we highlight diameter-dependent superlubricity of water in carbon nanotubes, with giant flow enhancements in the smallest tubes. In contrast, their boron-nitride analogues, which have the same crystalinity as CNT, exhibit no slippage. This shows that water-solid friction and interfacial slippage originates in subtle and even sub-atomic details of the solid-liquid interface.
Laboratoire Gulliver, ESPCI, Paris
"Effets Collectifs, Physique Statistique et Matière Molle"
Derrière la dénomination pas très heureuse de « Matière Molle » se cache la physique de nombreux systèmes que l’on rencontre au quotidien. Pâtes, suspensions, gels, mousses, émulsions, etc ont tous cette particularité d’être composés d’entités de tailles grandes devant les échelles atomiques et petites devant les échelles cosmologiques. Il en résulte plusieurs propriétés qui rendent leur étude particulièrement délicate. En effet, le plus souvent, ces systèmes sont hors-équilibre, désordonnés, et répondent non linéairement aux perturbations extérieures.
Au cours de cet exposé, j’essaierai d’illustrer sur deux exemples — la physique des verres et celle des fluides actifs — comment expériences modèles et physique statistique permettent, au travers d’un dialogue fructueux, de mettre à jour des comportements génériques, sinon universels, pour ces systèmes. L’exposé sera nourri d’exemples issus des recherches les plus actuelles du laboratoire EC2M.
Laboratoire de Physique Théorique, ENS, Paris
"Data-driven statistical mechanics model of collective biological behaviour"
Physicists have long hoped that the tools of statistical mechanics could help understand emergent behaviour in complex multi-agent biological systems - neuron networks, animal groups, etc. Until recently, most connections had remained at the stage of a metaphor. With the advent of increasingly accurate experimental measurements, it is now possible to build explicit statistical mechanics model of
collective behaviour directly from high-throughput data. The thermodynamics of these models can then be studied in their own right. I will show how this can be done in two examples : the collective coding of visual stimuli by the retina, in which we find evidence of a second-order phase transition, and the highly coordinated motion of bird flocks, which is described by the ordered phase of a classical interacting spin system.
"Nikita Kavokine : Oscillating Focus microscopy : towards a new tool for brain imaging"
Observing neuronal activity is a long standing challenge in the life sciences. Major progress has recently been achieved in this area, with the development of fluorescent proteins that allow to actually see the spikes of individual neurons, as a replacement for cumbersome electrode techniques. However, in order to obtain biologically relevant information, it is important to be able to image these proteins in real brain tissue, which is where existing optical microscopy techniques reach their sensitivity limit.
I have been working for 6 months in Adam Cohen’s lab at Harvard university on a new fluorescence microscopy technique, especially suited for the imaging of neural activity in brain tissue, which we called Oscillating Focus (OF) microscopy. The technique is based on a confocal microscope, where instead of a pinhole, oscillation of the focal spot and lock-in detection is used to ensure optical sectioning. I will explain how we used Monte Carlo simulations of light transport in the brain to validate the concept OF microscopy, and I will present the practical realisation of an OF microscope, with first results showing superior performance to conventional confocal microscopy.
"Jean Douçot : Tidal deformation of a rotating neutron star"
The study of the tidal deformations of compact objects has been recently pursued actively because of the implications for the gravitational waves emitted by binary systems. For nonrotating stars, the response to an external tidal field is characterized by the so-called Love numbers. The case of rotating stars is more complex because of couplings between the spin and the tidal perturbation. A perturbative analysis in general relativity reveals dynamical fluid motions in the star’s interior, but cannot distinguish between a response that is bounded or linearly growing in time. Further insight into the problem is given by a post-Newtonian analysis. In this framework, considering a gravitomagnetic tidal field, more explicit expressions for the fluid’s velocity perturbation can be obtained at first post-Newtonian order, which give the fully dynamical evolution of the fluid. The approach remains valid for non-stationary tidal fields, which is relevant for the orbital evolution of a binary system.
Santa Fe Institute, USA
"What physics can tell us about inference ?"
There is a deep analogy between statistical inference and statistical physics ; I will give a friendly introduction to both of these fields. I will then discuss phase transitions in two problems of interest to a broad range of data sciences : community detection in social and biological networks, and clustering of sparse high-dimensional data. In both cases, if our data becomes too sparse or too noisy, it suddenly becomes impossible to find the underlying pattern, or even tell if there is one. Physics both helps us locate these phase transiitons, and design optimal algorithms that succeed all the way up to this point. Along the way, I will visit ideas from computational complexity, random graphs, random matrices, and spin glass theory.
Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC)
"Condensed Matter between Knowledge and Innovation : More is different (and fun !)"
Condensed Matter Physics (CMP) explores the fundamental properties of matter and their origins resulting from the interactions of a large number of atoms and electrons. The intricate nature of these interactions results in properties and associated phenomena that often hint at a rich vein of underlying physics. Although the perspective is changing constantly with new discoveries, the basic challenges in CMP are to predict and observe new phenomena and elucidate novel properties of materials often pushing at the frontiers of quantum mechanics, as marvelously shown by the 2016 Nobel Prize in Physics, awarded to studies on quantum topological properties.
CMP is also a field which stimulates technological innovation that revolutionizes modern society. For more than five decades, the engine of CMP has largely been driven by semiconductor industry. Probably the most notable example is the invention of the transistor which was recognized by the 1956 Nobel Prize in Physics given to William Shockley, John Bardeen, and Walter Brattain.
There is a persistent interplay between the fundamental science and technological applications which provides breadth to CMP. One cannot possibly give full justice to the entire range of CMP problems that now command the attention of the condensed matter and materials physics community. Therefore, rather than even try, in this short essay we point out a few fundamental problems of major importance whose solution would further expand our understanding and Knowledge, while also mentioning some emerging functional properties of materials where the associated potential applications could foster the technological Innovation.
In the second part of the seminar I will present in all detail the Condensed Matter program of the ICFP Master 2nd year.
Institut de Physique Théorique, CEA Saclay
"Theoretical Physics"
What is theoretical physics ? What are the challenges, the methods and the current status of this field ? We will address these questions and then present the ICFP Master in theoretical physics. The aim is to show how the M2 cursus trains students to become leading theorists in physics and also in interdisciplinary fields.
Laboratoire de physique du solide, Univ. Paris Sud, Orsay
"Soft matter"
Institut Langevin, ESPCI, Collège de France, Paris
"From Time-Reversal Physics to Innovation"
Time-reversal invariance is a very fundamental concept in physics. The objective of this talk is to show how this concept can be turned into a huge source of innovations and successful start-up companies.
It was first in the field of acoustics and later for microwaves, where antenna array technology was available, that “time-reversal mirrors” have been built. Such mirrors allow to refocuses in space and time an incident wave field at the original source location regardless of the complexity of the propagation medium. Contrary to intuition, a remarkable property was shown : the more complex the propagation medium, the sharper the focus. Such results have plenty applications including medical imaging, therapy, telecommunications, human-machine interface and defense. An overview of these applications will be presented.
Laboratoire Kastler Brossel, ENS, Paris
"Topological quantum states of matter with atomic gases"
The Nobel prize in physics was awarded in 2016 to D. J. Thouless, D. M. Haldane and J. M. Kosterlitz for their discovery of topological phase transitions and phases of matter. We will discuss these notions on several examples related to superfluidity, such as supercurrents in a superfluid ring and the superfluid transition of two-dimensional Bose gases. These phenomena will be illustrated by recent experiments on ultracold atomic gases.
We will also present the Quantum Physics parcours of the ICFP Master.
Laboratoire de Physique Statistique, ENS, Paris
"La mécanique de l’origami"
Une fois pliée, une simple feuille mince peut présenter des comportements mécaniques
particuliers. Allant de la réponse mécanique globale de la feuille (étirement, torsion,
flexion, etc.) au phénomène de vieillissement, ils sont dus à un fort couplage entre les singularités plastiques que représentent les plis. D’un simple pli au papier froissé, nous mettrons en lumière la manière dont ces structures se construisent et se complexifient.
LPA, ENS, Paris
"Diamants en lévitation pour des tests en physique quantique avec des objets macroscopiques."
The recent developments in the field of opto-mechanics make it possible to cool mechanical oscillators close to their ground state of motion and to perform pristine quantum optical experiments with macroscopic objects. A difficulty for cooling typical macroscopic oscillators however is the thermalization due to the contact of the object to a structure. Various solutions have been envisionned to circumvent this issue, a prominant escape route being to levitate the object.
Inspired by recent achievements with hybrid opto-mechanical systems, cooling schemes using embedded quantum emitters have then been propounded since they have the potential to enlarge the scope of opto-mechanical studies to seek novel quantum optical paradigms. In this direction, experiments done with optically levitating nanodiamonds containing nitrogen-vacancy (NV) centers are the most advanced, but light scattering from the trapping laser affects the NV center’s photo-response which will in turn hinder the particule motional read-out. In my group, we bypass the optical trap approach by realizing an ion trap based quantum microscope for nanodiamonds containing NV centers.
This novel architecture will enable cooling of the center of mass of a nanodiamond close to the ground state of motion, observing quantum jumps of a mechanical oscillator, and remotely entangling the oscillations of two diamonds. The platform furthermore opens opportunities for studying fundamental phenomena in quantum optics and establish building blocks of future quantum-based technologies.
Schlumberger
"La Loi de Coulomb dans les Milieux Anisotropes"
La loi du Coulomb dans le vide ou dans des milieux diélectriques isotropes est bien connue depuis debut de 19ème siècle. Le potentiel électrostatique pour une charge ponctuelle diminue comme 1/r, menant à un champ électrique et un courant de déplacement polarisé radialement. Dans des milieux anisotropes aussi le potentiel électrostatique a une solution exacte. Cependant, le concept de distance Pythagorëen est généralisé à une "distance anisotrope".
Cette distance anisotrope donne un potentiel électrostatique avec des surfaces équipotentielles ellipsoïdales et un champ électrique qui est déformé de la direction radiale par la permittivité anisotrope tensorielle. En même temps, le courant de déplacement reste purement radialement orienté.
La solution exacte de la loi de Coulomb est généralisée aux ondes acoustiques compressionelles dans des milieux élastiques et dans des milieux poreux à l’écoulement de Darcy des fluides.
Laboratoire Charles Fabry, CNRS et Institut d’Optique, Palaiseau
"Simulation quantique dans des matrices d’atomes de Rydberg individuels"
CNRS & ESPCI, Paris
"Glass Transition at Interfaces"
LESIA-Université Paris Diderot-Observatoire de Paris
"Portrait of a comet : highlights from the ESA Rosetta mission"
Rosetta is the cornerstone mission of the European Space Agency devoted to the study of Solar System minor bodies. Launched on 2 March 2004, Rosetta arrived on August 2014, at the comet 67P/Churyumov-Gerasimenko after 10 years of interplanetary journey. After the successful delivery of the lander Philae on its surface on November 12, 2014, the Rosetta mission orbited around the comet for about two years, providing the unique opportunity to continuously investigate the 67P nucleus composition, activity, and its evolution during the orbit. A large complement of scientific experiments designed to complete the most detailed study of a comet ever attempted are on board Rosetta, including cameras, spectrometers in the UV-NIR range, radio science, dust and plasma analyser and so on. In this talk I will present the main results achieved from the different instruments of the orbiter, in particular from the OSIRIS imaging system, as well as the main results from the adventurous landing of Philae. Finally the implications of the results in the interpretation of the Solar System origin will be discussed.
RECRUTEMENT ACCES DIRECT
Le département de physique
Programme, cours et calendrier 2022 - 2023 