Accueil > Publications, documents > Séminaires

Séminaires

  • Alexandre Bouzdine (LOMA, Talence), le mercredi 04 Mars dans l'amphithéâtre de l'IOA à 11H45:

" Matière des vortex dans les supraconducteurs"

résumé :

"Le vortex comme objet quantique microscopique, histoire de la découverte et des propriétés essentiels.
Les méthodes d' observation des vortex. Le vortex dans les systèmes quasi-2d, formation des chaines de vortex et des molécules de vortex.
La charge électriques des vortex et leurs manipulations à l'aide de faisceau laser."

  • Francesco Minardi (Instituto Nazionale di Ottica INO-CNR, I-50019 Sesto Fiorentino, Italy) le mercredi 11 février dans l'amphithéâtre de l'IOA à 11H45:

"Quantum magnetism and impurities with mixtures of ultracold atoms in optical lattices "

résumé :

Ultracold atoms in optical lattices form a formidable experimental setting to investigate many-body physics. With two-components gases, Hamiltonian models traditionally used to describe interacting spins on a lattice can be experimentally realized, leading to a cold-atoms route to quantum magnetism. I will describe our efforts and results in the direction of observing the analogue of an antiferromagnetic phase with a two-species Bose-Einstein condensate. In addition, we use the same mixture with strongly imbalanced populations to observe the dynamics of impurities in a many-body quantum reservoir. Although the interpretation of our findings is still incomplete, a mass renormalization of the impurity atoms due to the formation of polarons, i.e. their dressing by the excitations of the bath, seems to occur.

Finally, educated from the limitations encountered with traditional optical lattices, i.e. standing waves, I will introduce a proposal for a novel way to realize periodic potentials with the help of nano-patterned surfaces featuring plasmonic resonances.

  • Adrien Aubourg (LP2N) le mercredi 21 janvier dans l'amphithéâtre de l'IOA à 11H45:

"Diode-pumped laser sources with Er : YAG single cristal fiber as gain medium "

résumé :

Among the several applications of laser sources, some requires kilometers range propagation in the atmosphere : telemetry, guidance system or active imagery. High pulse energy improves the range of the system, but may cause permanent blindness to an observer's eyes. Hence, these applications must use laser beam which wavelength are located in the eye-safe region, ideally at the local minimum of the atmosphere absorption (1550-1650 nm). Such laser sources are already commercially available, but are not suited for the demanding military needs : compacity, electrical consumption, performance and large operating temperature range (-40°C/+60°C).My work aims to develop a laser source filling these specifications. Thanks to the collaboration with the industrial partners Fibercryst and Cilas, it focuses on the design of a compact, efficient, directly diode-pumped Er3+:YAG single cristal fiber laser for military applications.With a homemade numerical simulation of a passively Q-switched Er3+:YAG laser source, many laser emitters are experimentally designed and compared. Further studies around saturable absorbers allowed sensible improvements of the output pulse energy.This work, whose results may already be commercially interesting, may lead to new technics and architectures of erbium doped solid-state laser for better prototypes.

  • Raphael Voituriez (Laboratoire de Physique Théorique de la Matière Condensée, Paris) le lundi17 novembre dans l'amphithéâtre de l'IOA à 11H45:

"First-passage times of random walks and kinetics of search processes : applications to transcription."

résumé:

à venir

  • Matthieu Palayret (University of Cambridge, UK) le lundi 6 Octobre Septembre dans l'amphithéâtre de l'IOA à 11H45:

"A zoom in CD28 super-agonist T cell activation with single-molecule localisation microscopy "

résumé :

CD28 is a transmembrane protein which co-stimulate the T cell receptor (TCR), leading to T cell activation. CD28 can also directly activate T cells in a TCR-independent way: resting T cells incubated with CD28 super-agonist in solution and dropped onto a surface coated with secondary antibodies proliferate and release IL-2. However, conventional antibodies with similar kinetic and binding constants do not activate them. This specificity (when bound to CD28, the super-agonist is 75 Å closer to the T cell surface than the conventional antibody), together with the importance of the coated surface in the experiments and recent discoveries about TCR triggering, points towards a possible role for the kinetic-segregation model.

The kinetic-segregation model assumes an equilibrium between phosphatases with large ectoplasmic domains (such as CD45 or CD48) and small transmembrane kinases (such as Lck) which respectively dephosphorylate and phosphorylate a receptor (such as the TCR). In a resting cell, this equilibrium induces a null net phosphorylation of the receptor, leading to no activation. However, when a close contact forms between the cell and a surface or another cell, the large phosphatases are physically excluded from the contact, allowing net phosphorylation of the receptor if it enters and stays long enough in the contact zone (when binding to its ligand for example).

We here study CD28 super-agonist TCR-independent activation. Both dynamics (to study the kinetics of CD28) and distribution (to study the segregation of CD45) of CD28 and CD45 are observed in live T cells upon activation. Because of the sub-diffraction size of the initial contact zones and the need for single molecule trajectories to study the kinetic-segregation model, we used single molecule localisation microscopy and single particle tracking techniques.

  • Rafal Mantiuk (Bangor University, (UK)) le lundi 30 juin dans l'amphithéâtre de l'IOA à 14H00:

"Towards a hyper-realistic display"

résumé :


"Today's computer graphics techniques make it possible to create imagery that is hardly distinguishable from photographs. However, a photograph is clearly no match to an actual real-world scene. I argue that the next big challenge in graphics is to achieve perceptual realism by creating artificial imagery that would be hard to distinguish from reality. This requires profound changes in the entire imaging pipeline, from acquisition and rendering to display, with the strong focus on visual perception. In this talk I will present two projects on computational displays, which adapt to the limitations and abilities of our visual perception. In the first project we modelled changes in image appearance between day- and night-vision (mesopic and scotopic) in order to simulate the appearance of night scenes on regular displays, or generate compensated images that reverse the changes in vision due to low luminance levels. The method can be used in games, driving simulators, or as a compensation for displays used under varying ambient light levels. In the second part I will talk about a work-in-progress on a hyper-realistic display system that delivers high dynamic range, high spatial resolution, binocular disparity and focal depth cues. I will discuss design and construction challenges and future direction of the research."

BIO:
----
Rafal Mantiuk is a senior lecturer (associate professor) at Bangor University (UK) and a member of a Reasearch Institute of Visual Computing. Before comming to Bangor he received his PhD from the Max-Planck-Institute for Computer Science (2006, Germany) and was a postdoctoral researcher at the University of British Columbia (Canada). He has published numerous journal and conference papers presented at ACM SIGGRAPH, Eurographics, CVPR and SPIE HVEI conferences, applied for several patents and was recognized by the Heinz Billing Award (2006). Rafal Mantiuk investigates how the knowledge of the human visual system and perception can be incorporated within computer graphics and imaging algorithms. His recent interests focus on designing imaging algorithms that adapt to human visual performance and viewing conditions in order to deliver the best images given limited resources, such as computation time or display contrast.

  • Ramon Hegedus (INRIA) le lundi 24 Février dans l'amphithéâtre de l'IOA à 14H00:

"Narrow Spectral Color Imaging - How to translate images for human color vision from outside of its domain?"

résumé :


" Narrow band imaging techniques generate images by selecting discrete bands over the full visible or even a wider spectral range. Contrary to this approach, the sampling can be also done with filters that altogether only cover a tight spectral window. Such an image acquisition method can be particularly useful when optical information is only available or of special interest within a narrow spectral range. Since the differences among images captured in such a spectral window can be extremely small, in order to get meaningful color images, visualization of the acquired data requires a novel approach. To this end a color mapping method is introduced, using which the input data can be transformed onto the entire display color gamut with a continuous and perceptually nearly uniform mapping, while ensuring an optimally high information content for human perception. In a broader context this work also points to the problems concerning how to render images for the human vision system that are produced by computational photographic approaches."

  • Séminaire Laphia: Thomas Udem (Max-Planck Institute for Quantum Optics, Garching, Allemagne), le jeudi 13 Février 2014 dans l'amphithéâtre de l'Institut d'Optique d'Aquitaine à 14h30 ::

"Ultrahigh-Resolution Spectroscopy of the Hydrogen Atom"

Affiche_udem (DOCX / 1,29 MB)
Udem_publication (PDF / 135,62 kB)
  • Alexandre Cazé (Institut Langevin ESPIC), le lundi 16 Décembre dans la salle E200 de l'Institut d'Optique à 14H00:

"Probing strongly scattering media with speckle correlations"

résumé :


"When a disordered medium is illuminated with coherent light, a complex intensity pattern arises, called speckle. Due to fundamental constraints on light propagation (energy conservation, reciprocity, ...), correlations appear in these patterns. In this presentation, we will give a brief introduction on speckle correlations, and address the two following questions:

- What is the correlation between the transmitted and the reflected speckle obtained by illuminating a slab of disordered medium with a laser?

- How is the intensity correlation function affected by the interaction between the source and the scattering medium?"

  • Eric Burt (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA) le vendredi 13 Décembre dans la salle E200 de l'institut d'optique à 14H00:

"Next Generation JPL Ultra-Stable Trapped Ion Atomic Clocks"

résumé :


"Over the past decade, trapped ion atomic clock development at the Jet Propulsion Laboratory (JPL) has proceeded in two parallel directions: 1) new atomic clock technology for space flight applications that require strict adherence to size, weight, and power requirements, and 2) ultra-stable atomic clocks, usually for terrestrial applications focusing on ultimate performance. In this talk I will present first results from two new ultra-stable trapped ion clocks in the second category currently under development. The new identical clocks, designated L10 and L11, build on the successful demonstration of exceptionally low drift at the 3x10-17/day level by their predecessor, LITS-9, with changes in design intended to further improve ultimate long-term performance. I will discuss how this level of performance is achieved in a room temperature frequency standard as well as the motivation for doing so. This includes both practical and scientific applications such as tests of the equivalence principle and studies of isotopic properties such as the hyperfine anomaly. Finally, I will describe how one of the new standards will be used as a ground terminal reference for the Atomic Clock Ensemble in Space (ACES) project."

  • Etienne Gaufrès (Université de Montréal, CANADA), le vendredi 15 Novembre dans la salle E200 de l'Institut d'Optique d'Aquitaine à 9H30:

"Etude des phénomènes physiques opto-électroniques de molécules encapsulées dans les nanotubes de carbone"

résumé :

Raman spectroscopy uses visible light to acquire vibrational fingerprints of molecules, thus making it a powerful tool for chemical analysis in a wide range of media. Its potential for detecting compounds at the single molecule level is, however, severely limited by the fact that the Raman effect is weak. Recently, we reported the discovery of a giant Raman scattering effect from dye molecules encapsulated and aggregated inside single-walled carbon nanotubes (SWNTs). [1] Measurements performed on rod-like dyes, such as -sexithiophene and -carotene, assembled inside SWNTs as highly polarizable J-aggregates indicate a resonant Raman cross-section (CS) of (3±2)×10-21 cm2/sr, which is well above the CS required for detecting individual aggregates at the highest optical resolution. This scattering cross section enables the determination of different regimes in the encapsulation isotherms of the 6T inside carbon nanotubes with sensitivity down to 10 molecules [2]. These encapsulated dyes have other properties such as quenched fluorescence background, no photobleaching and simple functionalization process. These features make them ideal to used as nanoprobe labels for Raman bio-imaging and multispectral analysis.[1]

[1] Giant Raman Scattering from J-Aggregated Dyes inside Carbon Nanotubes for Multispectral Imaging,
Gaufrès et al, Nature Phot. (Just accepted)
[2] Encapsulation Isotherms of α-sexithiophene inside Single-Walled Carbon Nanotubes
Gaufrès et al, (submitted)

  • S. Lepoutre (LCAR, Toulouse), le mardi 15 octobre dans la salle E201 de l'Institut d'Optique d'Aquitaine à 14H00:

"Mesures de précision par interférométrie atomique à bras séparés"

résumé :


"Dans ce séminaire, je présenterai les travaux réalisés pendant mon doctorat au Laboratoire Collisions Agrégats Réactivité (LCAR, Toulouse) sous la direction de Jacques Vigué. J'ai utilisé un interféromètre atomique de Mach-Zehnder pour mesurer une interaction de Van der Waals atome-surface, et pour détecter une phase topologique découverte théoriquement par He, McKellar et Wilkens. La source atomique est un jet supersonique de lithium. Trois ondes stationnaires laser quasi-résonantes réalisent successivement la séparation, ré exion puis recombination de l'onde atomique par di raction dans le régime de Bragg. Les bras de l'interféromètre sont séparés dans l'espace, autorisant une perturbation sélective de leur propagation pour observer la modi cation des franges d'interférences atomiques. Des signaux intenses et de fortes visibilités permettent d'obtenir une sensibilité en phase e ective de 30 mrad/sqrt(Hz).
La mesure de l'interaction de Van der Waals a été réalisée en collaboration avec l'équipe d'A. Cronin (University of Arizona, Tucson). Un des bras de l'interféromètre interagit avec un réseau matériel de dimensions nanométriques, ce qui donne accès à l'amplitude complexe de di raction dans l'ordre 0 par le réseau. Des mesures de faible incertitude ont été réalisées pour une gamme étendue de vitesses atomiques, et ont mis en évidence une dépendance à la vitesse inhabituelle mais bien expliquée par un modèle théorique. Ces mesures se sont aussi avérées sensibles à une éventuelle interaction gravitationnelle non-Newtonienne de très courte portée (1-10 nm), fournissant des contraintes comparables à celles d'autres expériences de physique atomique.
L'e et Aharonov-Bohm (AB), découvert en 1959, est induit lorsqu'une particule chargée se propage dans un potentiel vecteur : c'est le premier exemple de phase topologique en interférométrie d'ondes de matière, un sous-groupe des phases géométriques découvertes par Berry. En 1984, Aharonov et Casher
ont prouvé qu'une phase similaire existe (la phase AC) lorsqu'un dipole magnétique se propage dans un champ électrique. En 1993-1994, He, McKellar et Wilkens ont montré l'existence d'une troisième phase topologique, duale électromagnétique de l'e et AC : la phase HMW, induite lors de la propagation d'un
dipole électrique dans un champ magnétique. Bien que l'existence des phases AB et AC est établie par diverses expériences, la phase HMW n'avait pas été détectée avant ces travaux. Pour la mesurer, nous avons appliqué des champs électriques opposés sur les deux bras de l'interféromètre a n d'induire des
dipoles opposés, qui se propagent dans un champ magnétique uniforme. Avec ce dispositif, la phase HMW a une valeur de l'ordre de 10 mrad, comparable ou inférieure à diverses phases parasites induites par les défauts inhérents au montage. Une importante étude expérimentale et théorique a interprété
ces e ets systématiques pour extraire une première mesure de la phase HMW, néanmoins relativement imprécise. A sa suite et après mon départ de l'équipe, des expériences complémentaires réalisées avec un dispositif amélioré ont con rmé sa valeur théorique avec une précision de quelques pourcents, ainsi
que son caractère topologique."

  • Rémi Galland (Interdisciplinary Institute for Neuroscience, Bordeaux) ,le lundi 16 septembre dans l'amphitheatre du Labri à 14H00:

"Optical tools for biology: From single molecules based approaches to directed proteins self organization"

Light provides very efficient tools to observe and study biological processes but also to direct, modify or quantify biological mechanisms and functions. Through fluorescence, light enables to observe biological mechanisms with resolution up to tens of nanometers and 3D capabilities. Higher energy enables to excite non linear processes and confine the light effect in 3D giving additional resolution and a way to directly act within a living cell. In my talk, I will introduce several optical tools I developed to study biological processes such as self-organization mechanisms in cells and also to control those processes for the emerging field of the bio-inspired technologies.

First, I will present a multi-FCS system that enables to simultaneously record at various locations the dynamical properties of fluorescent species. It has been used to study the aggregation behaviours of proteins in vivo depending of external stimuli. Next, I will show different laser-based patterning systems that allow to dynamically control the cell shape and/or cytoskeleton assembl and thus create reproducible actin networks within cells and/or in vitro. I then used the geometrical constraints given by those laser-based patterning systems combined with an accurate control of the biomechemical environment to control both the shape and the orientation of 3D actin-based structures. This control and the development of an electroless metallization process have led to the realization of actin-based 3D conductive connections. This work provides an alternative way to generate connections in 3D microelectronic circuits based on an innovative bioinspired self-assembly approach. Finally, I will present different way to improve the 3D capabilities of the Single Melcule Localisation Microscopy both in term of axial resolution and in term of depth of field that can be imaged. Such capabilities would enable to image with high resolution whole cells or even cellular aggregates, which could lead to a better understanding of the complex interactions and organizations of proteins in vivo.

  • David Pabœuf (Institute of Photonics - University of Strathclyde, Glasgow), le jeudi 4 Juillet dans l'amphitheatre du Labri à 14H00:

"Laser à semi-conducteur pompé optiquement émettant dans l¹UV et stabilisé en fréquence"

résumé :

"Les lasers en cavité externe émettant par la surface (ou VECSELs) sont devenus, depuis une quinzaine d¹années, un moyen attractif pour réaliser une source laser accordable, de puissance élevée et avec une excellente qualité de faisceau. Grace à la disponibilité de milieux à gain semi-conducteur différents éventuellement combinée à de la conversion non linéaire, ces lasers couvrent actuellement une large partie du spectre lumineux allant de l¹ultraviolet au proche infrarouge [1,2]. Un aspect particulièrement intéressant de ces lasers est leur dynamique interne; le temps de vie des photons dans la cavité étant bien plus grand que celui des porteurs cela réduit très fortement la limite de Schawlow-Townes, ce qui laisse espérer l’obtention d’un faisceau laser de très grande pureté spectrale avec un faible bruit d’intensité à partir d’un VECSEL.

Je présenterai nos récents travaux, effectués à l¹Université de Strathclyde, allant dans ce sens et concernant une source laser émettant dans l¹ultraviolet basée sur un VECSEL émettant dans le rouge et doublé en fréquence. La fréquence de ce laser est asservie sur le flanc de frange d¹une cavité Fabry-Perot de référence [3].

1. S. Calvez, J. E. Hastie, M. Guina, O. G. Okhotnikov, and M. D. Dawson, "Semiconductor disk lasers for the generation of visible and ultraviolet radiation," Laser & Photonics Reviews 3, 407­434 (2009).

2. N. Schulz, J.-M. Hopkins, M. Rattunde, F. Bussières, and J. Wagner, "High-brightness long-wavelength semiconductor disk lasers," Laser & Photonics Review 2, 160­181 (2008).

3. D. Pabœuf, P. J. Schlosser, and J. E. Hastie, "Frequency stabilization of an ultraviolet semiconductor disk laser," Optics Letters 38, 1736 (2013)."

  • Philippe Ben-Abdallah (LFC, IOGS Palaiseau), le lundi 17 Juin dans l'amphithéatre du LABRI à 14H00:

"Transfert de chaleur en champ proche et contrôle de l’émission thermique à l’aide de systèmes plasmoniques complexes"

résumé :

"Tout corps chaud émet dans son environnement des photons du fait de la présence des fluctuations thermiques. Ces photons transportent à la fois de l’énergie et de la quantité de mouvement. Lorsqu’un second corps est placé dans le voisinage de cet objet les photons émis par ces objets induisent une force d’interaction et un transfert net de chaleur du corps le plus chaud vers le corps le plus froid.

Dans ce séminaire je montrerai comment il est possible de modifier les propriétés d’émission en champ lointain et en champ proche de systèmes plasmoniques en interaction. J’aborderai ensuite le problème du transport de la chaleur dans les systèmes à N-corps . Enfin je discuterai de quelques applications potentielles de cette physique dans le domaine de la conversion d’énergie de champ proche."

  • F. Wetzel et J. Kaes ( Universität Leipzig, Faculty of Physics and Earth Sciences, Institute for Experimental Physics I, Linnéstr. 5, 04103 Leipzig, Germany), le lundi 3 juin dans l'amphithéâtre du LABRI à 14H00:

"Biomechanical Phenotyping of Primary Breast Cancer Cells and Determination of Impact Factors "

résumé :

"Malignant tumors are not aggregations of homogeneous cells but rather complex formations of diverse cell types and pathological cells in different stages of aggressiveness. Recent investigations show that the biomechanical properties of benign cells differ from those of cancerous and metastatic cells.

In order to characterize these biomechanical properties, primary mamma carcinoma cells are used for measurements and compared to cells obtained from breast reduction. In the course of this clinical trial, samples from 13 breast cancer patients were analyzed. Single cells obtained by enzymatic dissociation of the homogeneous sample are measured using the Optical Stretcher, a two beam laser trap enabling contact-free, whole cell elasticity measurements. Various impact factors such as culture conditions, age and drug treatment were identified. Considering this, we found that cells from tumor samples have a broader distribution in deformability than benign cells, the whole distribution being shifted to higher deformability. These distribution are non-Gaussian, they have a positive skew which means a “long tail” towards higher deformations. After deformation, tumor cells retract towards their original shape. This relaxation behavior is stronger for malignant cells, single cells even contract against the applied stress.

These findings will help to improve our picture of the heterogeneous nature of tumor samples, detailed analysis of the “long tail” and contractile cells might lead to new knowledge about metastatic competent, disseminated and cancer stem cells."

  • Florian Fahrbach ( Laboratory for Bio- and Nano-Photonics, Department of Microsystems Engineering, University of Freiburg, Germany), le Mercredi 22 Mai dans l'amphithéâtre du Labri à 14H00:

"Light-sheet microscopy with holographically shaped self-reconstructing beams"

  • Adam Rancon (Université de Chicago), le mardi 21 Mai dans l’amphithéâtre du Labri à 14H00:

"Quantum Phase Transition and universal thermodynamics of a Bose gas"

résumé :


"Basing myself on recent experiments on cold atoms, I will discuss the universality of the thermodynamics of the two-dimensional dilute Bose gas, shown for instance by the fact that the pressure depends only on the ratio of the chemical potential over the temperature and on the interaction strength through a universal (scaling) function. I will show that this universality is due to a quantum phase transition between the vacuum (no particles) and the superfluid phase. I will then discuss the thermodynamics near the phase transition between a Mott insulator and a superfluid which happens in cold atoms loaded in an optical lattice (described by the Bose-Hubbard model). In particular, I will show that the thermodynamics of this strongly interacting system is described by the same universal functions that apply for the dilute gas. "

  • Rémi Carminati (ESPCI), le lundi 29 Avril dans l’amphithéâtre du Labri à 14H00:

"Nanosources, photons et désordre : nano-optique en milieux complexes"

résumé :

"L’interaction entre des sources fluorescentes et des milieux diffusants, éventuellement nanostructurés, est au cœur de questions d’actualité en photonique :

Peut-on détecter et localiser des molécules fluorescentes dans un milieu diffusant et désordonné (comme un tissus biologique) ? Peut-on concevoir des matériaux amorphes pour amplifier l’interaction lumière-matière ? Peut-on utiliser des modes localisés par le désordre pour des études fondamentales en photonique ?

Nous illustrons la richesse du mariage de l’émission spontanée et de la diffusion multiple sur des exemples couvrant la plasmonique sur des films désordonnés, les fluctuations de fluorescence dans des matériaux diélectriques diffusants, ou la transition vers le couplage fort avec des modes localisés d’Anderson. "

  • Ivo Ihrke (INRIA) le lundi 8 Avril dans l'amphithéâtre du Labri à 14H00:

"Computational Optical Measurement and Display"

résumé :


"Advances in imaging technology have to a large extent shaped scientific progress in the last 200 years. While progress in imaging technology originated in, and forced the development of, the field of optics, the design paradigm for optical instruments has always placed the human observer at the center of its efforts. With the advent of electronic computation in the second half of the 20th century, optical design could be elevated to a new level by exploiting computer-aided design and automated optimization procedures. However, only in recent years have computers become so powerful, and at the same time so small and inexpensive, that imaging technology, storage and transmission have become completely digitized. This move has not yet reached its full potential since the human observer is still considered the target of optimization, whereas in fact, today's primary observers are computers. It is this insight that enables a new approach to optics and measurement instrumentation. Images no longer have to mimic what the human brain is accustomed to interpret as an image of the world, i.e. integrals over ray bundles of a restricted subset of the electro-magnetic spectrum. Instead, sensing mechanisms can be designed that re-distribute directional, spatial, temporal and wavelength information to essentially agnostic sensor elements serving as simple photon collectors. The questions of how such redistribution can be arranged for, which performance characteristics are to be expected of such devices, and how these novel sensing means can be used for measurement purposes form the basis of my research. I will discuss several example applications and outline future developments that I think will be necessary for further progress. "

  • Philippe Lalanne (LP2N) le lundi 18 Mars dans l’amphithéâtre du Labri à 14H00:

"lumière lente, nanoparticules complexes pour l'optique, absorption des plasmons de surface "

résumé :

"Le séminaire a pour objectif de présenter mes projets de recherche actuels à Bordeaux et l'état de "mes réflexions" pour monter une équipe de recherche au LP2N qui prend en compte au mieux les compétences que j'ai identifiées à l'Université.
Mon projet sur la lumière lente est déjà lancé, mais d'autres projets sont encore en cours de maturation, comme celui sur les nanoparticules complexes pour la photonique, et enfin d'autres encore autour du transfert radiatif assisté par les plasmons, en particulier, restent plus prospectifs, au stade de la réflexion.
Je vais essayer de présenter le tout de manière informelle. "

  • Vincent Studer (Interdisciplinary Institute for Neuroscience, Bordeaux 2), le lundi 4 Mars dans l'amphithéâtre du Labri à 14H00:

"Fluorescence microscopy based on compressed sensing "

résumé :


"In fluorescence microscopy, one can distinguish two kinds of imaging approaches, wide- field and raster scan microscopy, differing by their excitation and detection scheme. In both imaging modalities the acquisition is independent of the information content of the image. Rather, the number of acquisitions N, is imposed by the Nyquist-Shannon theorem. However, in practice, many biological images are compressible (or, equivalently here, sparse), meaning that they depend on a number of degrees of freedom K that is smaller that their size N. Recently, the mathematical theory of compressed sensing (CS) has shown how the sensing modality could take advantage of the image sparsity to reconstruct images with no loss of information while largely reducing the number M of acquisition.
Here we present a novel fluorescence microscope designed along the principles of CS. It uses a DMD (Digital Micromirror Device) to create structured wide-field excitation patterns and a sensitive point- detector to measure the emitted fluorescence. On sparse fluorescent samples (beads, and cultured cell), we could achieve compression ratio N/M of up to 64, meaning that an image can be reconstructed with a number of measurements of only 1.5 % of its pixel number.
Furthemore, we demonstrate how CS acquisition schemes can be extended to an hyperspectral imaging system. We could acquire fluorescence images, with 128 different spectral channels, with a compression ratio of up to 128. We finally discuss strategies to further reduce the number of acquisition by taking into account the sample sparsity, not only in the spatial but also in the spectral domain."

  • Jean-Paul Salvetat (CRPP), le lundi 25 février dans l'amphithéâtre du Labri à 14H00:

"Micromanipulation et façonnage d'ultramicroélectrodes en nanotubes de carbone multiparois "

résumé :

"En introduction nous discuterons de l'intérêt des nanotubes de carbone pour l'électrochimie, de la difficulté de fabriquer des ultramicroélectrodes en nanotubes, et du problème toujours ouvert de la réactivité électrochimique des matériaux graphitiques. Des éclairages récents ont été apportés grâce à des expériences réalisées sur du graphène. Nous les résumerons.

Nous présenterons ensuite nos résultats sur la fabrication et la caractérisation d'ultramicroélectrodes en nanotubes de carbone multiparois fabriqués par méthode CVD. L'exposé sera centré sur les aspects techniques du problème. Côté résultats, nous verrons que le courant stationnaire mesuré en voltammétrie cyclique en solutions aqueuses et dans des liquides ioniques est en accord avec les modèles classiques d'électrodes cylindriques ou annulaires. Le problème de l'évaluation de la cinétique de réaction est par contre plus délicat à traiter. Des pistes seront évoquées pour aller plus loin. "

  • Lev Khaykovich (Bar-Ilan University, Israel and Laboratoire Kastler Brossel, France), le lundi 11 Février dans l'amphithéâtre du Labri à 14H00:

"Universal few-body physics in ultracold atoms"

résumé :


" Few-body systems with resonantly enhanced two-body interactions display universal properties in the sense that they are independent of the details of the short-range interaction potential. The central paradigm in the three-body domain, predicted in the early 1970s by V. Efimov, is associated with the infinite ladder of universal bound states with discrete scaling invariance. This curious prediction avoided experimental verification in different systems for decades, and only recently and exclusively surrendered to ultracold atoms. I will describe the remarkable progress in experimental investigation of the Efimov scenario with the emphasize to our studies performed with ultracold bosonic lithium."

  • Valentina Krachmalnicoff (ESPCI), le lundi 28 Janvier dans l'amphithéâtre du Labri à 14H00:

"Sonde nanometrique pour l’imagerie sub-longueur d’onde de la densité locale d’états électromagnétiques"

résumé :


"Cet exposé porte sur l'étude expérimentale et théorique des fluctuations de la densité locale d'états électromagnétiques en champ proche d'une nanoantenne d’or. La densité locale d'états électromagnétiques est une quantité fondamentale qui caractérise la réponse optique dans un environnement structuré. Cette grandeur peut être utilisée pour sonder des environnements complexes ou pour concevoir des matériaux structurés en vue d'un contrôle de l'absorption ou de l'émission de la lumière.

Pour mesurer la densité locale d'états électromagnétiques à l'échelle nanométrique, nous avons utilisé un microscope à force atomique (AFM) à pointe active. Ceci est réalisé en greffant au bout de la pointe d’un AFM un émetteur fluorescent de taille nanométrique. En combinant notre AFM avec un microscope confocal de fluorescence, nous sommes en mesure d'enregistrer simultanément la carte d’intensité de fluorescence, du taux de désexcitation fluorescente (proportionnel à la densité locale d'états électromagnétiques) et de la topographie de l'échantillon avec une résolution sub-longueur d’onde. Les cartes d’intensité de fluorescence et de la densité locale d'états électromagnétiques fournissent des informations complémentaires. Leur acquisition simultanée est cruciale pour obtenir une caractérisation complète des propriétés optiques d’une nanoantenne plasmonique ou, plus en général, d’un échantillon complexe plasmonique ou diélectrique."

  • Bruno Laburthe-Tolra (Laboratoire de Physique des Lasers, Université Paris 13), le lundi 21 Janvier dans l'amphithéatre du Labri à 14H00:

"Propriétés magnétiques d’un condensat dipolaire"

résumé :


"Du fait de leur fort moment magnétique (6 magnétons de Bohr), les atomes de Chrome interagissent assez fortement via l’interaction dipôle-dipôle. Cette interaction, anisotrope et de longue portée, modifie les propriétés des condensats obtenus. Ce séminaire portera en particulier sur l’effet des interactions dipolaires sur un condensat spinoriel (c’est-à-dire possédant un degré de liberté de spin) ; les atomes peuvent être considérés comme de petits aimants quantiques qui interagissent à longue distance, ce qui permet d’étudier la physique du magnétisme.
Dans une première série d’expériences, nous avons étudié le diagramme des phases magnétiques d’un nuage ultra-froid de Chrome. A haute température et bas champ magnétique, le nuage, thermique, se dépolarise spontanément du fait des interactions dipolaires. A plus basse température, la condensation de Bose-Einstein induit une polarisation spontanée du nuage, qui traduit la nature ferromagnétique du condensat : le condensat se forme dans un état de spin polarisé. A très bas champ magnétique, cependant, lorsque les interactions dépendant du spin sont plus grandes que l’énergie Zeeman, on observe une transition de phase qui conduit à la dépolarisation spontanée du condensat.
Dans une autre série d’expériences, le magnétisme des atomes de chrome est étudié après avoir chargé un condensat dans un réseau optique tri-dimensionnel. Ce magnétisme en réseau présente de fortes analogies avec le magnétisme quantique (modèle d’Heisenberg). Je présenterai des résultats de dynamique de spin dans ce régime"

  • Philipp Haslinger (Quantum Nanophysics and Molecular Quantum Optics Faculty of Physics, University of Vienna), le lundi
    14 Janvier dans l'amphithéâtre du Labri à 14H00:

"Exploring and exploiting the quantum superposition of macromolecules and molecular clusters"

résumé :


"In the past century quantum physics has developed from an intriguing theory with daring Gedanken experiments to one of the most precisely studied and verified theories of nature.
Recent experimental advances have allowed us to devise new molecular sources, interferometer arrangements and detection methods that open the path to testing quantum mechanics for massive macroscopic particles with highest sensitivity.
I will focus on our latest interferometer which uses pulsed optical gratings. This allows us to conduct experiments in the time-domain where the particles don´t experience velocity-dependent dephasing. The gratings are realized by standing light waves of a nanosecond laser beam at λ = 157 nm. This wavelength is short enough to achieve single photon ionization of a broad range of atoms, molecules and nanoparticles. In combination with an external electric field these pulses act as absorptive gratings in the time-domain. On the applied side this interferometer can be used as a nanoruler for high-precision measurements of internal particle properties."

  • Valery V. Ryazanov (Institute of Solid State Physics, Russian Academy of Sciences), le lundi 17 Décembre dans la salle de conférence de l'IPF (batiment A4 3ème étage) à 14H00:

"Hybrid superconductor/ferromagnet Josephson structures and bottlenecks
of ultrafast superconducting electronics"

résumé :

Superconducting single-flux-quantum (SFQ) digital circuits offer unique features that include not only high-speed operation (> 100 GHz) with low power (< 1 μW/gate at 100 GHz), but also the use of superconductive transmission lines that transmit pico-second SFQ pulses over centimeters at the speed of light with negligible loss, dispersion, and crosstalk. Apart from “cryophobia” the current SFQ digital circuits have two main disadvantages: too large master cell and the lack of dense, fast, energy efficient memory electrically compatible with the traditional SFQ circuits. The main goal of the talk is to show that recent fundamental physics research in superconductor-ferromagnet thin-film structures (SF-structures) created a new opportunity to solve this long-standing problem.

Superconductivity and ferromagnetism, two deeply antagonistic electronic properties, can coexist in form of Josephson SFS junctions (SFS JJ) [1]. The most impressive feature of the SFS JJ is the ability to be in a Josephson state with the phase difference inversion or p-state [2,3]. The physical origin of the superconducting phase inversion is a spatial variation of the superconducting order parameter in the ferromagnet arising as a response of the Cooper pair to an energy difference between the two electron spin directions [4]. The inclusion of a p-junction into a superconducting loop results in superconducting phase inversion [5] and generates spontaneous flux (phase shift) [6]. This feature makes the SFS JJs valuable phase-shifting elements for utilization in superconducting circuits. Recently, a Toggle Flip-Flop (TFF) with the embedded SFS p-junction was successfully demonstrated [7]. The use of SFS p-junctions can lead to a smaller circuit area and larger operation margins. The SFS JJs are also suitable for integration with Josephson qubits. A quantum Josephson circuit, a p-biased phase qubit, has been recently demonstrated too [8].

It was also shown that the critical current of an SFS JJ can be changed significantly by remagnetization of the F-interlayer [1]. A Josephson magnetic memory element proposed in Ref. [9,10] requires ferromagnet layer with an in-plane magnetic anisotropy and small coercive field. Specifically, an application of small external magnetic field changed the magnetization of the ferromagnetic layer that in turn changes the junction critical current Ic, allowing the realization of two distinct states with high and low Ic, corresponding to logical “0” and “1” states, respectively. It was demonstrated too in Ref.[11] that by inserting an additional isolation tunnel layer (I) in the SFS JJ (i.e., fabricating a superconductor-insulator-ferromagnet-superconductor (SIFS) structure), one should be able to increase significantly the junction characteristic voltage Vc to achieve high switching frequency. The superconducting-ferromagnetic Josephson junctions are electrically compatible with traditional superconductor-insulator-superconductor (SIS) Josephson junctions used for digital energy-efficient single flux quantum (eSFQ/ERSFQ) circuits. Both SFS and SIS Josephson junction circuits have similar fabrication process and can be integrated on a single chip. As a result, a combination of SFS and SIS JJs can be used to form addressable memory cells, energy-efficient memory periphery circuits and programmable logic elements.

  1. V.V. Ryazanov, Physics – Uspekhi 42, 825 (1999).
  2. V.V. Ryazanov, V.A. Oboznov, A.Yu. Rusanov, A.V. Veretennikov, A.A. Golubov, and J. Aarts, Phys. Rev. Lett 86, 2427 (2001).
  3. V. A. Oboznov, V.V. Bol'ginov, A. K. Feofanov, V. V. Ryazanov and A.I. Buzdin, Phys. Rev. Lett. 96, 197003 (2006).
  4. A.I. Buzdin, Rev. Mod. Phys. 77, 935 (2005).
  5. S.M. Frolov, D.J. Van Harlingen, V.A. Oboznov, V.V. Bolginov, and V.V.Ryazanov, Phys. Rev B 70, 144505 (2004).
  6. S.M. Frolov, M.J.A. Stoutimore, T.A. Crane, D.J. Van Harlingen, V.A. Oboznov, V.V. Ryazanov, A. Ruosi, C. Granata, and M. Russo. Nature Physics 4, 32 (2008).
  7. M. I. Khabipov, D.V. Balashov, F. Maibaum, A.B. Zorin, V.A. Oboznov, V.V. Bolginov, A.N. Rossolenko and V.V. Ryazanov. Superconductor Science and Technology, 23, 045032 (2010).
  8. A.K. Feofanov, V.A. Oboznov, V.V. Bol’ginov, J. Lisenfeld, S. Poletto, V.V. Ryazanov, A.N. Rossolenko, M. Khabipov, D. Balashov, A.B. Zorin, P.N. Dmitriev, V.P. Koshelets and A. V. Ustinov. Nature Physics 6, 593 (2010).
  9. V.V. Bol’ginov, V.S. Stolyarov, D.S. Sobanin, A.L. Karpovich, and V.V. Ryazanov, JETP Letters 95, 366 (2012).
  10. V.V. Ryazanov, V.V. Bol’ginov, D.S. Sobanin, I.V. Vernik, S.K. Tolpygo, A.M. Kadin, and O.A. Mukhanov, Phys. Procedia 36, 35 (2012).
  11. T.I. Larkin, V.V. Bol’ginov, V.S. Stolyarov, V.V. Ryazanov, I.V. Vernik, S.K. Tolpygo, O.A. Mukhanov, Appl. Phys. Lett. 100, 222601 (2012).
  • Simon Bernon (Physikalisches Institut, Eberhard-Karls-Universitat Tubingen),le lundi 3 Décembre dans l'amphithéâtre du labri à 14H00:

"Interfacing cold atoms and superconducting micro-structures"

résumé:

"Hybrid quantum systems, which combine ultra-cold atoms with superconducting solid-state devices, have been proposed in the aeras of precision sensing and quantum information processing. Such systems will exploit the rapidity of quantum logical operations performed by solid-state devices together with the long coherences time of atomic quantum superposition states.

We report here on the interfacing of ultracold atoms of 87Rb and superconducting Niobium microstructures at 4.2 K. The atomic cloud is magnetically trapped and prepared on a superconducting atomchip. Degenerate ensembles containing 106 to 104 atoms at 100 nK are generated in the hyperfine ground state |F=1,mF=-1>. The creation of such large and cold ensembles is one of the prerequisite to the collectively enhanced interaction that is requested for quantum information protocols. In addition, due to the strong cryo-pumping of our system, very long lifetimes of thermal and BEC clouds are demonstrated.

Preserving the coherence of quantum superposition state in a cryognenic environment is a key issue for the storage of quantum information. In this work, we investigate, by ramsey measurements, the spin coherence obtained on a superconducting atomchip. We demonstrate comparable performance to the state of the art at room temperature, and show the influence of the close proximity of a superconducting microwave coplanar cavity.

As a further step towards the interfacing of these two quantum systems, we implemented an interconnected hybrid trap involving a Ioffe trap and the magnetic field deformation generated by a super-current in a superconducting ring. The trap deformation and the quantization of flux in the ring are inviestigated. In particular, it was shown that the atomic cloud was sensitive to the change of a single flux quanta. This work opens new possibilities in coupling cold atoms and quantum superpositions of flux."

*

Actualités