A novel and versatile way to prepare thin, transparent, flexible and homogeneous films of advanced and multi-component materials has been developed by our research group. The so-called liquid/liquid interfacial route (LLIR) is a new pathway to design materials combining synthesis and processing in one single-pot and single-step, allowing the production of multi-components and multi-functional thin films for application in different fields. This talk will demonstrate the huge potentiality of LLIR to prepare novel and exclusive multicomponent films of different mater, highlighting conducting polymers- and 2D-based nanocomposites. Application of the resulting materials in different fields as electrodes in aqueous and transparent Na- or K-ion batteries, transparent electrodes, electrochromic displays, catalysts and sensors will also be shown.

Gaugino condensation on D-branes wrapping internal cycles gives a mechanism to stabilize the associated moduli. According to the effective field theory, this gives rise, when combined with fluxes, to supersymmetric AdS4 solutions. In this paper we provide a ten-dimensional description of these vacua. We first find the supersymmetry equations for type II AdS4 vacua with gaugino condensates on D-branes, in the framework of generalized complex geometry. We then solve them for type IIB compactifications with gaugino condensates on smeared D7-branes. We show that supersymmetry requires a (conformal) Calabi-Yau manifold and imaginary self-dual three-form fluxes with an additional (0,3) component. The latter is proportional to the cosmological constant, whose magnitude is determined by the expectation value of the gaugino condensate and the stabilized volume of the cycle wrapped by the branes. This confirms, qualitatively and quantitatively, the results obtained using effective field theory. We find that exponential separation between the AdS and the KK scales seems possible as long as the three-form fluxes are such that their (0,3) component is exponentially suppressed. As for the localized solution, it requires going beyond SU(3)-structure internal manifolds. Nevertheless, we show that the action can be evaluated on-shell without relying on the details of such complicated configuration. We find that no “perfect square” structure occurs, and the result is divergent. We compute the four-fermion contributions, including a counterterm, needed to cancel these divergences.

Despite its great triumph, nowadays it is well-know that the Standard Model (SM) of particle physics remains an incomplete theory, as a range of unsolved questions persist. In this context, the search for phenomena that lie beyond the SM gains even greater significance. Although originally such searches focused on the evidence of new heavy particles, more recently several experiments have become capable of probing dark sectors with feebly interacting light particles, pushing particle physics to the 'intensity frontier' era. In this talk, I will discuss the theory and phenomenology of different minimal BSM extensions related to the three possible renormalizable interactions (‘portals’) connecting the new dark sector and the SM. In particular, I will focus on models that introduce new light particles such as the dark photon, the dark Higgs, and axion-like-particles.

Nous avons étudié la force de Casimir-Lifshitz (CLF) entre des nanostructures à base de graphène, à l'équilibre et hors équilibre thermique, i.e. entre deux feuilles de graphène posées sur un substrat diélectrique se faisant face dans diverses conditions thermiques. Nous avons également étudié la CLF entre deux réseaux de graphène à l'équilibre thermique. Pour analyser ce problème, nous avons utilisé l'approche de la matrice de diffusion (S-matrix), qui nécessite des méthodes numériques efficaces pour être calculée. Parmi ces méthodes, nous avons adapté la Méthode Modale de Fourier équipée de fonctions de base locales (FMM-LBF : Fourier Modal Method - Local basis Functions) en incidence conique. De plus, nous avons étendu cette méthode pour analyser des structures cylindriques recouvertes de bandes de graphène [1]. En ce qui concerne la CLF entre des réseaux de graphène posés sur des substrats diélectriques, nous avons observé une variation notable de celle-ci en fonction du potentiel chimique. Par la suite, nous avons examiné son comportement non-additif et constaté que, pour de petites séparations (d = 60 nm), la non-additivité est relativement faible. En conséquence, nous pouvons utiliser en toute confiance une méthode additive beaucoup plus directe et rapide pour calculer la force avec une précision de quelques pourcents. Cependant, la situation est tout à fait différente pour de plus grandes séparations (d = 200 nm). À cette distance, il y a un effet non-additif significatif, entraînant des écarts allant jusqu'à 30% par rapport à la prédiction additive. Nous avons aussi découvert que cette influence non-additive peut être modulée in situ en ajustant le potentiel chimique du graphène, sans nécessiter de changements dans la géométrie ou les matériaux du système [2]. Après cela, nous avons exploré la CLF en dehors de l'équilibre thermique entre deux couches de graphène à deux températures différentes dans un bain thermique à une troisième température [3]. Contrairement au cas usuel, où la force est toujours attractive dans des conditions d'équilibre, notre étude montre que la force peut être ajustée pour devenir répulsive si l'environnement est à basse température. Nous montrons également que pour obtenir des variations significatives de la CLF, il est essentiel de maintenir une basse température pour les feuilles de graphène, qu'elles soient en équilibre ou hors équilibre thermique. Enfin, nous constatons que la dépendance de la CLF hors équilibre en fonction du potentiel chimique devient non monotone dans une certaine plage de distances. Les différentes approches théoriques et méthodes numériques développées dans cette thèse nous permettrons, dans un futur très proche, d'explorer d'autres situations intéressantes comme le transfert de chaleur et la CLF hors équilibre thermique entre deux réseaux de graphène, la CLF entre un cylindre diélectrique couvert partiellement de graphène et un plan, ou encore le torque de Casimir dans différentes nano-structures à base de graphène.

[1] Youssef Jeyar, Mauro Antezza, and Brahim Guizal. Physical Review E, 107(2):025306, 2023.

[2] Youssef Jeyar,  Minggang Luo, Kevin Austry, Brahim Guizal, Yi Zheng, H. B. Chan, and Mauro Antezza. arXiv:2306.17640, 2023

[3] Youssef Jeyar, Kevin Austry, Minggang Luo, Brahim Guizal, H. B. Chan, and Mauro Antezza. Physical Review B, 108,115412, 2023.

Active matter is a broad class of materials within which individual entities, the active particles, consume energy in order to perform movement. These materials are at the intersection of many distinct fields of research, such as biology, engineering, and physics, and have thus attracted considerable attention. Because of their perpetual consumption of energy, these systems are out of thermodynamic equilibrium. As a consequence they display a wealth of surprising phenomena which challenge our conception of equilibrium phases and dynamics. Among them, collective motion is particularly intriguing and exciting on multiple grounds. First because it emerges in systems with distinct length and time scales, from collections of cells to large crowds, flocks, and swarms, yet with some common characteristics. This thus suggests some sense of universality in the mechanisms leading to different collective behaviours. Second because parts of these motions display signatures shared with other equilibrium phenomena. While the latter are very diverse, ranging from the glass transition to inertial turbulence, these connections mean that a number of concepts and tools are readily available to describe out-of-equilibrium behaviours. Third because the possible applications of the understanding and control of these phenomena are far-reaching: treatment of specific pathologies, design of intelligent materials, crowd management, etc. In this Thesis, we focus on dense active matter, where the movement of individual particles is hindered by crowding effects, and aim to characterise how this competition leads to emerging collective motion. To this effect we use a simple model of two-dimensional isotropic self-propelled particles, namely active Ornstein-Uhlenbeck particles, where the departure from the equilibrium limit is controlled via the persistence time of propulsion forces. Owing to its simplicity, the phenomena described within this model have the potential to apply to a broad range of materials. We broadly map the phase behaviour of this model, from the equilibrium-like regime at small persistence to the to far-from-equilibrium regime at large persistence. We focus our efforts on the latter regime, where velocity correlations were recently shown to emerge. We demonstrate that a disordered liquid phase exists up to very large persistence, if polydispersity frustrates the ordering of the system, and that this persistent liquid displays various manifestations of disordered collective motion. First, we show that persistent systems are dynamically arrested at large packing fraction. Close to dynamical arrest, we find that the liquid displays dynamical heterogeneity similar to equilibrium dense systems. We investigate, in the idealised limit of infinite persistence, the microscopic processes leading to these heterogeneities. Then, away from dynamical arrest, we show that our model displays chaotic advection flows, as typically shown by turbulent systems. We highlight how this specific behaviour may be universal to a broader class of active systems relying on the competition of crowding and persistent forcing. Finally, in monodisperse systems which display long-range order at large packing fraction, we describe the far-from-equilibrium mechanisms leading to structural relaxation.

Individual bacteria transported in viscous flows, show complex interactions with flows and bounding surfaces resulting from their complex shape as well as their activity. Understanding these transport dynamics is crucial, as they impact soil contamination, transport in biological conducts or catheters, and constitute thus a serious health thread.

Here we investigate the trajectories of individual E-coli bacteria in confined geometries under flow, using microfluidic model systems in bulk flows as well as close to surfaces using a novel Langrangian 3D tracking method. Combining experimental observations and modeling we elucidate the origin of upstream swimming, lateral drift or persistent transport along corners.

The quest for efficient spin-photon interfaces is at the core of many proposals in quantum optics. On the one hand, it would allow developing deterministic spin-photon and photon-photon gates for quantum computing, as well as multi-entangled states with N photons, for quantum communications. On the other hand, it would allow implementing interesting fundamental studies on quantum measurement, whereby each photon can be used to « observe » the spin system.

In this seminar, I will briefly review some systems used for spin-photon coupling, and then focus on the recent progress made in C2N, using charged quantum dots in pillar-based cavities. I will show how we can use the same device as a quantum emitter – to emit several photons all entangled with the same spin, or as a quantum receiver – to allow exchanging the quantum information between a confined spin and the incoming photons.


Along the way, I will show how one can play with the polarization degree of freedom in various ways, to encode multi-photon entanglement as well as to extract information on the various processes occurring in our solid-state structures.

Finally, I will discuss some perspectives of our work, for the realization of optimized spin-photon interfaces and their use in various applications.