Séminaires doctorants

Exposés des doctorants en deuxième année de thèse.


21/09/2018 site Sophia
Publication : 21/09/2018
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10:00

Bonnefond Sylvain

Amplification de la lumière par diffusions multiples dans des systèmes vivants

Notre objectif est de valider une nouvelle technique pour améliorer la détection des faibles signaux émis par quelques fluorophores dans un échantillon biologique. Cette technique est basée sur des travaux récents portant sur l’amplification stimulée de la lumière via la diffusion multiple. L’idée principale est d’introduire des nanoparticules dans un milieu biologique fluorescent où celles-ci diffusent et renforcent l’émission stimulée permettant de produire une quantité suffisante de fluorescence à la sortie de l’échantillon biologique.

Une longue phase de tests préliminaires, encourageants et reproductibles, a été menée sur la stabilisation et la dispersion des nanoparticules dans un milieu physiologique [2], milieu défavorable à celles-ci causant leur agrégation, condition désavantageuse pour obtenir l’amplification de la fluorescence.

Actuellement, nos efforts sont portés sur la réduction progressive de la quantité de nanoparticules en recherchant un compromis entre une amplification suffisante et une biocompatibilité tolérable pour les cellules.

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10:17

Boughdad Omar

Fluids of light in complex media

Quantum fluids of light merge many-body and nonlinear optics, through the study of light propagation in a nonlinear medium under the shine of quantum hydrodynamics. One of the most outstanding evidence of light behaving as an interacting fluid is its ability to carry itself as a superfluid. Here, we report a direct experimental detection of the transition to super- fluidity in the flow of a fluid of light past an obstacle in a bulk nonlinear crystal. In this cavityless all-optical system, we extract a direct optical ana- log of the drag force exerted by the fluid of light and measure the associated displacement of the obstacle. Both quantities drop to zero in the super- fluid regime characterized by a suppression of long-range radiation from the obstacle. The experimental capability to shape both the flow and the poten- tial landscape paves the way for simulation of quantum transport in complex systems.

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10:34

Cipris Ana

Cooperative scattering of light in cold atomic clouds

Cooperative effects arise from collective interaction of ensemble of atoms with light. Such an interaction is different from interaction of light with individual atoms. Thus, understanding and exploiting these differences is of main interest.
One of the objectives of this research is study of subradiance, cooperative phenomena in spontaneous emission that exhibits decreased emission rate in comparison to spontaneous emission of light from single atom. Furthermore, of great interest is Anderson localization, absence of diffusive wave transport in media. Anderson localization of light in cold atomic clouds and its relation to subradiance are to be studied in this research.
I will present aim and objectives of my research, as well as research methodology.

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10:51

Gouzien Elie

Description quantique de la gigue temporelle pour les détecteurs ON/OFF de photons uniques

Un type de détecteurs très utilisé en optique quantique est le type “ON/OFF”, suffisamment sensible pour détecter un photon mais incapable d'en préciser le nombre quand il y en a plusieurs. Ces détecteurs de photons uniques indiquent également le temps de détection. Néanmoins, cette mesure souffre de fluctuations aléatoires : la gigue temporelle, qui est actuellement un facteur limitant pour de nombreuses applications de l'information quantique, en imposant, par exemple une limite au débit et à la précision de protocoles exploitant des mesures de coïncidences.
Afin de pallier à ces problèmes et pouvoir évaluer quantitativement les effets de la gigue dans des situations expérimentales communes, nous avons mis au point une description quantique de la mesure effectuée par un détecteur ON/OFF en modélisant les effets de la gigue et en prenant en compte ceux du temps mort et de l'efficacité finie. Ce travail qui relève de l'optique quantique multimode nous a permis de décrire les détecteurs de photons non idéaux par des opérateurs positifs de mesure (POVM).
Nous avons appliqué ensuite ce résultat à l'étude des effets de la gigue temporelle sur des expériences habituelles de l'optique quantique. En particulier, comme je le détaillerai dans mon exposé, nous avons étudié le cas d'une source de photons annoncés, pour laquelle une post-sélection sur le temps d'annonce permet d'augmenter la qualité de l'état généré.
Dans ma présentation je vous exposerai ces résultats ainsi que le travail sur l'optique multimode que je prévois pour ma dernière année.

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11:08

Kukhaleishvili Nino

Physics of invasive fungal growth

The fungus Candida albicans is a commensal yeast that is found on mucosal surfaces of the gastrointestinal and urogenital tract in most healthy individuals. However, this organism can cause superficial as well as life-threatening systemic infections in response to alterations of its environment, and is particularly aggressive in immuno-compromised individuals. A switch from budding to filamentous growth is critical to invade host tissues [1], as well as to burst out of host macrophages.

The aim of this interdisciplinary project is to examine the biophysics of filamentous growth of this human fungal pathogen. The project uses a combination of micro-fabrication, live cell microscopy, physical measurements and modeling in order to understand how C. albicansadapts itself while invading. 

To determine quantitative relationships between physical forces (due to turgor pressure) and cell growth, we are growing C. albicansin micro-chambers, composed of polydimethylsiloxane(PDMS), of different stiffness [2]. We are following C. albicansinvasion as a function of substrate resistance, in order to study growth speed and tip shape. We are also mimicking C. albicansinvasion by indentation of a macroscopic probe into the substrate [3], in order to understand rupture behavior (crack, friction, adhesion) of the PDMS. I have generated PDMS microchambers of different stiffness and measured their viscoelastic properties. By combining microscopic observations with rupture behavior, we will be able to quantify the internal pressure for wild type and several cell wall mutants.

References

[1] SheppardDC, FillerSG. Cold Spring Harb Perspect Med. 2014 Nov 3;5(1):a019687.

[2] Minc et al.  Current Opinion in Microbiology 2015

[3] Fakhouri et al. Soft Matter 2015

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11:25

Mondain François

Generation and detection of squeezing on chip

Squeezed light exhibits reduced noise properties with respect to « classical light » such as that emitted by standard laser sources. Its characteristics make it a good candidate for a wide variety of applications from quantum communication to quantum metrology and quantum computation. In order to comply with future out-of-the-lab implementations, squeezing experiments must rely on compact and miniaturized set ups : in particular the miniaturisation concerns the squeezing generation stage, typically relying on bulk optical parametric oscillators, as well as the detection, based on homodyne-like optical interferometers.
In this context, we developed a compact squeezing experiment based on a home made-lithium niobate chip. The chip includes the generation stage, based on a non-linear optical waveguide and an optical coupler, which is the main
component of the homodyne interferometer. With such a device, we recently measured a squeezing level corresponding to a noise reduction of - 2 dB with respect to the classical limit.
During this seminar, I will present these results and the work I will conduct during my last PhD year on the manipulation of squeezed states.

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11:42

Neradovskaia Elizaveta

Periodical poling in Congruent Lithium Niobate crystals with slanted polar axis

The mid-IR is defined as 2-20 μm spectral range with a number of so-called “water windows”, representing wavelength of light which can propagate through Earth’s atmosphere without absorption by water vapor [1]. Moreover, most molecules have distinct absorption lines in the mid-IR, providing a fingerprint that makes it possible to identify them by optical spectroscopy [2].
To realize the optical frequency mixers adapted to the ultra-short pulses sources (<100 fs) and high average power (above 10 W) in mid-IR it is necessary to have non-linear components offering large aperture (about 1 cm2). The periodically poled non-linear optical crystals lithium niobate (LN) and lithium tantalate are well suited to the optical parametric amplification in the mid-IR due to wide transparency range and high non-linearity, but the usual poling technique is not suitable for producing the components with required large aperture.
In order to overcome this technological barrier, the “slanted poling” (or axis-slant QPM) have been demonstrated [3]. The essence of the method is to produce periodical grating in plate with slanted polar axis, specifically in 25o X-cut MgO-doped LN (MgO: LN). In our work we investigated 36o Y-cut congruent LN (CLN) crystals, which are used for surface acoustic wave devices. The main advantages of these crystals are low price and great offer on the market.

1. D. Lubin, J. Clim. 7, 121 (1994).
2. J.E. Bertie, Z. Lan, Appl. Spectrosc. 50, 1047 (1996).
3. H. Ishizuki, T. Taira, Opt. Mater. Express 1, 1376 (2011).

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11:59

Mejia Morales Julian

Detection and implementation of cells deformation

The study of the Young's modulus of the cells is a tool to determine its state of health. To analyze the elasticity of the cells is necessary apply a force stimulus to deform them and a detection method to measure the response. For the deformation, acoustic radiation pressure it is being implemented to apply force on the particles and thus deform them. Two methods of detection are sought, one of rapid measurement and one of detailed measurement. For the rapid measurement a low Finesse Fabry-Pérot interferometer has been implemented. While for the detailed analysis, the reconstruction of the cellular volumetric profile by means of the transport of intensity equation has been chosen. The advances and preliminary results of the deformation and detection methods are presented, as well as the possible scope.