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

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)