Soft and wet contact arises in a range of phenomena that spans many length and time scales, and includes : landslides, aquaplaning of tires, wear of industrial bearings, ageing of synovial and cartilaginous joints, cell motion in blood vessels or microfluidic devices, and atomic-force or surface-force rheology. Therein, the coupling between boundary elasticity and confined viscous flow leads to a striking zoology of counterintuitive emergent effects. From the canonical situation of a free particle that can simultaneously sediment, slide, and roll in a viscous fluid, and near a soft wall, we study a range of novel inertial-like (despite the low-Reynolds-number flow) features, such as : enhanced sedimentation, elastohydrodynamic bouncing, roll reversal, emergent lift and torque...

In this talk, I will discuss various possibilities of producing dark matter in the early universe. By describing the transition between an inflationary epoch to a late time cosmology, I will emphasize how the dynamics of the universe can affect dark matter production and leave a cosmological imprint, allowing some of these scenarios to be constrained.

In this talk, I will describe the connection of two geometric objects: Apollonian (sphere) packings and knots. Both objects have several applications in mathematics, physics, chemistry and computer science. Indeed, recent models in soft and condensed matter use Apollonian packings as a simple discrete method to describe foam structures, polydisperse emulsions or granular crushing. On the other hand, knotted and linked molecules appear naturally in biopolymers like proteins, DNA or RNA. In biochemical synthesis, there is a great interest on developing methods for the construction of knotted and linked synthetic molecules, since they reveal greater elasticity than simple molecules. I will give a brief survey on the geometry behind Apollonian packings, and I will present new methods for the construction of optimal knotted and linked structures based on a 3D generalization of Apollonian packings.

Joint work with Jorge L. Ramírez Alfonsín.

Engineering robust solid-state quantum systems is amongst the most pressing challenges to realize scalable quantum photonic circuitry. While several 3D systems (such as diamond or silicon carbide) have been thoroughly studied, solid state emitters in two dimensional (2D) materials are still in their infancy.
In this presentation I will discuss the appeal of an emerging van der Waals crystal – hexagonal boron nitride (hBN). This unique system possesses a large bandgap of ~ 6 eV and can host single defects that can act as ultra-bright quantum light sources. In addition, some of these defects exhibit spin dependent fluorescence that can be initialised and coherently manipulated. On top of that, the hBN crystals can be carefully sculpted into nanoscale photonic resonators to confine and guide light at the nanoscale. It hence has all the vital constituents to become the leading platform for integrated quantum photonics. To this extent, I will highlight the challenges and opportunities in engineering hBN devices and will frame it more broadly in the growing interest with 2D materials nanophotonics.

We study N=1 superconformal theory in the context of AdS/CFT correspondence in the large central charge limit using Chern-Simons formulation of 3d gravity. In this limit conformal dimensions of a subclass of so-called light primary superfields remain finite and are governed by osp(1|2) subalgebra of N=1 super-Virasoro algebra. We describe the construction of osp(1|2) conformal blocks in terms of Wilson lines of the Chern-Simons 3d gravity. We consider examples of two and three-point blocks on the sphere and one-point torus blocks of light superprimary fields, which belong to finite-dimensional representations of osp(1|2). We study the correlation function for lower and upper components of the primary osp(1|2) doublets and show that the associated conformal blocks are obtained via Wilson line construction in Chern-Simons theory.

An analog simulator is a synthetic physical system, which emulates in a controlled way a physical problem. You can get answers about the physical problem by directly performing experiments on the simulator. In the present seminar, I will present the polariton platform and explain how it is relevant for analog simulation of many interesting complex problems.
Cavity polaritons are hybrid exciton-photon quasi-particle emerging from the strong coupling regime between photons confined in an optical cavity and excitons confined in quantum wells. They present physical properties reflecting their mixed nature. From the photon part, they inherit a small effective mass and can be confined in lattices with typical dimensions of the order of a few microns. Their excitonic part endows them with inter-particle interactions resulting in a giant Kerr non linearity. Moreover the system is intrinsically open and out of equilibrium because photons constantly leak out from the cavity. Cavity polaritons have been shown to present fascinating properties such as Bose Einstein condensation at elevated temperature, superfluidity, multistability etc [1].
In the present talk, I will explain how the polariton plateform is particularly suitable to realize analog simulation of open complex systems and explore fundamental physical phenomena.
I will describe a few recent results of our group:
1) How do wave localize in exotic quasi-crystals and how fractality does develop? This physics can be emulated with polariton lattices [2]
2) Polariton condensates are out of equilibrium and their phase dynamics has been predicted to obey the celebrated Kardar Parisi Zhang (KPZ) equation. We have been able to reveal experimentally universal KPZ scaling laws in the first order coherence of a 1D polariton condensate.[3]
3) Polariton lattices are also very interesting for the investigation of topological photonics. In particular, the ability to drive the system with controlled phases opens a new paradigm for non-linear topological photonics. [4]

References :

[1] C. Ciuti & I. Carusotto, Quantum fluids of light, Rev. Mod. Phys. 85, 299 (2013)
[2] V. Goblot et al. Emergence of criticality through a cascade of delocalization transitions in quasiperiodic chains, Nature Physics 16, 832 (2020)
[3] Q. Fontaine et al., Observation of KPZ universal scaling in a one-dimensional polariton condensate, arXiv:2112.09550 (2021)
[4] N. Pernet et al., Topological gap solitons in a 1D non-Hermitian lattice, arXiv:2101.01038 (to appear 2022)

Liquids are usually described within classical physics, whereas solids require the tools of quantum mechanics. I will show how in nanoscale systems this distinction no longer holds. At these scales, liquid flows may in fact exhibit quantum effects as they interact with electrons in the solid walls. I will first discuss the quantum friction phenomenon, where charge fluctuations in the liquid interact with electronic excitations in the solid to produce a hydrodynamic friction force [1]. Using many-body quantum theory, we predict that this effect is particularly important for water flowing on carbon-based materials, and we obtain experimental evidence of the underlying mechanism from pump-probe terahertz spectroscopy [2]. I will then show how the theory can be pushed one step further to describe hydrodynamic Coulomb drag – the generation of electric current by a liquid in the solid along which it flows. This phenomenon involves a subtle interplay of electrostatic and electron-phonon interactions, and suggests strategies for designing materials with low hydrodynamic friction [3].

[1] N. Kavokine, M.-L. Bocquet and L. Bocquet. Fluctuation-induced quantum friction in nanoscale water flows. Nature 602, 84-90 (2022).
[2] X. Yu, …, M. Bonn and N. Kavokine. Water-mediated electron cooling in graphene. In preparation.
[3] B. Coquinot, L. Bocquet and N. Kavokine. Quantum feedback at the solid-liquid interface: flow-induced electronic current and negative friction. ArXiV 2205.03250.

Zoom link: contact J. Palmeri, L2C

Scaling black holes are solutions of supergravity with multiple black hole singularities, which can be adiabatically connected to a single center black hole solution. We develop techniques to determine partition functions for such scaling black holes, if each constituent carries a non-vanishing magnetic charge corresponding to a D4-brane in string theory, or equivalently M5-brane in M-theory. For three constituents, we demonstrate that the partition function is a mock modular form of depth two, and we determine the appropriate non-holomorphic completion using generalized error functions. From the four-dimensional perspective, the modular parameter is the axion-dilaton, and our results show that S-duality leaves this subset of the spectrum invariant. From the five-dimensional perspective, the modular parameter is the complex structure of a torus $T^2$, and the scaling black holes are dual to states in the dimensional reduction of the M5-brane worldvolume theory to $T^2$. As a case study, we specialize the compactification manifold to a K3 fibration, and explicitly evaluate holomorphic parts of partition functions.