À : Campus Jussieu, 4 pl. Jussieu, Paris 5é, Amphi 55A , à 10:00

Animal behavior unfolds across multiple temporal and spatial scales, emerging from the integration of morphological, biomechanical, and physiological constraints with ecological demands. Traditionally, neuroscientists have approached this complexity by simplifying behavior—reducing its dimensionality and studying it primarily as a direct, easily measurable readout of neural activity. However, recent advances in computer vision and data acquisition are enabling more naturalistic approaches to behavioral neuroscience, giving behavior itself a more central role: first to understand its ecological relevance, and then to investigate its neural underpinnings. This work contributes to this shift. We developed a customized freely swimming assay to generate a comprehensive dataset of exploratory behavior in Danionella cerebrum across early development. This animal model was chosen for its small size and stereotyped behaviors, which facilitate detailed behavioral analysis, and its miniature, transparent brain, which enables future longitudinal whole-brain calcium imaging at cellular resolution. We analyzed the dataset from a dual perspective: first, we identified a developmental transition from continuous to intermittent locomotion, which we interpret as an emergent property of phenotypic maturation and adaptive motor control; second, we examined how internal drives structure large-scale navigation in an open environment. Together, our findings reveal how multiscale locomotor dynamics emerge from the interplay between body, brain, and environment during development.

À : Institut de la Vision, 17 Rue Moreau, 75012 Paris, salle Lusseyran , à 14:00

Optical wavefront engineering has become essential in imaging—whether for dynamic focusing, point-spread-function engineering, or aberration correction. The miniaturization of optical systems has recently created a strong need for devices capable of precisely manipulating wavefronts within micrometric pupils. In this thesis, we investigate a micrometer-scale wavefront-shaping method called “SmartLens”. An engineered micro-resistor locally modifies the temperature and, through the thermo-optical effect, the refractive-index distribution within a transparent polymer slab to precisely shape the transmitted wavefront. We first analyze the response time of these systems using numerical simulations and experimental measurements based on advanced wavefront-imaging techniques. We then exploit the tunability, transparency, and compactness of SmartLenses to demonstrate refocusing at the distal end of a sub-millimeter-pupil micro-endoscope. To enable aberration correction, we propose and demonstrate a strategy that reconfigures the generated wavefront through a dynamic shaping of the temperature distribution, based on the independent control of concentric resistors. We thus demonstrate a bimodal micro-optical element which can be tuned as a converging/diverging lens and a positive/negative spherical-aberration corrector.

À : Amphitéatre Jules Horowitz Centre CEA Saclay D306 / Porte Est, 91190 Saclay , à 13:30

Cette thèse étudie l’influence de l’hydrogène sur la plasticité des métaux cubiques centrés (CC), en particulier le tungstène. À basse température, la déformation de ces métaux repose sur le mouvement des dislocations vis $\frac{1}{2}\langle 111 \rangle$. Des calculs DFT montrent que l’hydrogène se ségrège fortement dans les deux configurations de cœur (facile et difficile) avec des énergies similaires. Des modèles d’Ising et des simulations de dynamique moléculaire avec un potentiel Machine Learning confirment cette ségrégation. De nouveaux calculs DFT révèlent aussi une forte affinité de l’hydrogène pour les lacunes, limitant sa disponibilité sur les dislocations. La mobilité des dislocations présente deux régimes : un blocage ou une accélération par rapport au tungstène pur selon la température-contrainte-concentration nominale en H. Étendue à d’autres métaux CC, l’étude montre que les interactions H-défauts sont faibles dans le groupe 5, fortes dans le groupe 6 et dans le fer.

À : Ecole Polytechnique, Route de Saclay 91128 PALAISEAU Cedex, Amphi Becquerel , à 15:00

À : Campus Jussieu, 4 Place Jussieu, Paris 5ème, Salle à déterminer

This thesis focuses on the creation and manipulation of Non-Gaussian states to test emerging heterogeneous quantum networks. These networks connect multiple physical platforms via optical communication, requiring various optical encoding strategies. We develop criteria to evaluate the quality of different encodings and benchmark tools for reliable information transfer. Using high-quality optical parametric oscillators and heralding via superconducting nanowire single-photon detectors, we create two optical encodings: one representing a two-level system and the other a harmonic oscillator. The two-level system involves photon-number superpositions, while the harmonic oscillator encoding is based on optical Schrödinger cat states. We demonstrate that these encodings can be entangled, making them suitable for use in network protocols. We improve the fidelity and projectivity of all-optical linear Bell-state measurements by combining single-photon detection with field quadrature selection. Additionally, we propose a criterion to evaluate the Non-Gaussianity of quantum coherences and apply it to two experimental two-level systems. Lastly, we explore the potential for generating error-correctable Non-Gaussian states. This work supports the use of multiple encodings in quantum networks and enhances methods for state creation and measurement in optical quantum communication systems.

À : Amphithéâtre Jules Horowitz - INSTN, Centre CEA Saclay D306 / Porte Est, 91190 Saclay , à 13:30

À : Jussieu Amphi 45A , à 13:45

Turbulence is a phenomenon that appears everywhere in nature, from oceans to galaxies. In quantum fluids, it takes the form of tiny vortices that interact with each other. These vortices can annihilate, rotate together, or give rise to new structures. Our experiment allows us to observe these dynamics using fluids of light, created by sending a laser through an atomic vapor. This produces a two-dimensional quantum fluid that is fully controllable and observable. With this platform, we explore how vortices behave, from highly turbulent situations with many vortices down to simpler cases with only a few. This lets us observe rare phenomena such as localized solitons, leapfrogging vortex pairs, or defects that move on their own. This work opens a new path toward understanding turbulence and out-of-equilibrium behavior in quantum systems.

À : Librairie LUMEN, 8 Av. des Sciences, 91190 Gif-sur-Yvette , à 14:00

La compréhension usuelle de l’interaction solide-liquide est que ce sont des effets de proche surface qui prédominent, plus loin, les deux media sont indépendants. Au cours des dernières décennies, il fut prouvé expérimentalement que les liquides proches de surfaces adhérentes, dites hydrophiles, se comportent comme des solides, indiquant un caractère vibrationnel à long portée. Est-ce que ces vibrations interagissent avec celles du solide? Cette thèse examine cette interaction là par le biais de méthodes expérimentales précises (rayons-X et diffusion neutronique dans de grands instruments). Nous montrons l’impact sur les vibrations à longue portée dans le solide lorsque le liquide est en écoulement sur la surface. Nous avons donc mis en évidence un nouveau type d’interaction, que nous interprétons comme indicative de l’état vibrationnel du liquide de type solide et de son couplage avec le solide alimenté par l’écoulement.

À : Campus Jussieu, 4 Place Jussieu, 57005, Amphi 25 , à 10:00

Quantum fluids of light are based on the mathematical mapping between the Gross- Pitaevskii equation, which describes weakly interacting Bose-Einstein condensates, and the propaga- tion of a laser through a nonlinear Kerr medium. In our case, the medium inducing the effective photon-photon interactions is a hot rubidium vapor. We can then study superfluidity, and more generally Bose gas physics, in a photonic system. This thesis pushes this platform to the realization of a two-component quantum fluid of light. We show that the two circular polarizations of light follow coupled Gross-Pitaevskii equations, and can therefore be considered as the two components of a binary Bose gas. We characterize the intra- and inter-component interactions and demonstrate the realization of a two-component fluid of light in the miscible and in the non-miscible regime. In the miscible regime, we proceed to the measurement of the elementary density and spin excitations, and reconstruct the characteristic two-branch dispersion of a superfluid mixture. In the non-miscible regime, we initiate the fluid into an homogeneous mixture to study the spontaneous separation of the two components into domains, also called coarsening dynamics. We numerically and theoretically model this phenomenon, which exhibits universal scaling dynamics, and obtain experimental results at short evolution time. To finish, we also experimentally show that the non-miscible binary fluid is a promising platform to study hydrodynamic instabilities at the interface of the two components, like the Rayleigh-Taylor and Kelvin-Helmholtz instabilities.

À : C2N Amphitheatre, 10 Boulevard Thomas Gobert, 91120 Palaiseau, France , à 14:00

This thesis explores two topics at the intersection of nanophotonics, nonlinear dynamics, and neuromorphic engineering using integrated photonic and optomechanical crystal cavities. In the first part, we investigate the synchronization of two self-pulsing photonic crystal nanocavities. Starting from the design, fabrication, and full characterization of a single self-pulsing cavity, we then study both unidirectional and bidirectional synchronization regimes. Rich dynamical phenomena are revealed, including multi-frequency locking, phase slips, and asynchronous states, all backed by detailed experiments and simulations. In the second part, we turn to the spiking (all-or-none) dynamics of an electro-optomechanical crystal cavity. By combining optical and electrical control of the mechanical resonance, we achieve the spiking behavior, the manipulation of the spiking threshold, temporal summation, and refractory period—key ingredients of biological neuron-like behavior. Experimental results are in good agreement with our theoretical and numerical predictions.