Complex and nonlinear fluids of light – CONFOCAL

Our analytical methods include diagrammatic theories for light in disordered environments, non-equilibrium Bogoliubov methods and kinetic theories to treat the interactions. These techniques are complemented by extensive numerical simulations of nonlinear Schrödinger equations. The project also involves collaborations with experimental research groups currently working on fluids of light.

Our work has recently shown evidence for a number of very interesting effects occurring during the propagation of a fluid of light in a cavityless nonlinear medium. By moving away from the paraxial limit, for instance, a fluid of light tends to exhibit optical spin-orbit interactions [1]. This discovery motivates, in particular, the use of fluids of light as quantum simulators of condensed-matter phenomena. In another example, we have explored the non-equilibrium dynamics of a two-dimensional, isolated, disordered fluid of light until its complete thermalization. When the latter is effective, the fluid can either be in a «normal« or in a superfluid state depending on the relative strength of disorder and interactions. In between these two states, a Kosterlitz-Thouless phase transition shows up, to our knowledge yet never observed for light.

A long-term perspective of the project is the systematic description of the interplay between disorder, spin-orbit coupling and photon interactions in a fluid of light. In particular, because of the different nature of the spin-orbit interaction of light as compared to massive particles, we may expect a different physics from the one of cold atomic gases, for instance. On the experimental side, an observation and fine characterization of a Kosterlitz-Thouless transition for light, or of more complex phenomena like the emergence of an insulating phase due to the disorder (many-body localization) constitute major challenges.

[1] G. I. Martone, T. Bienaimé, N. Cherroret,  Spin-orbit-coupled fluids of light in bulk nonlinear media, Phys. Rev. A 104, 013510 (2021)
[2] L. Tessieri, Z. Akdeniz, N. Cherroret, D. Delande, P. Vignolo,  Quantum boomerang effect: beyond the standard Anderson model, Phys. Rev. A 103, 063316 (2021)
[3] N. Cherroret, T. Scoquart, D. Delande,  Coherent multiple scattering of out-of-equilibrium interacting Bose gases, Annals of Physics (2021) 168543
[4] T. Scoquart, P.-E. Larré, D. Delande, N. Cherroret,  Weakly interacting disordered Bose gases out of equilibrium: from multiple scattering to superfluidity,  EPL 132 (2020) 66001
[5] T. Scoquart, T. Wellens, D. Delande, N. Cherroret,  Quench dynamics of a weakly interacting disordered Bose gas in momentum space, PRResearch 2, 033349  (2020)
[6] J. Janarek, D. Delande, N. Cherroret, J. Zakrzewki,  Quantum boomerang effect for interacting particles, Phys. Rev. A 102, 013303 (2020)
T. Bardon-Brun, S. Pigeon, N. Cherroret, Classical Casimir force from a quasi-condensate of light, PRResearch 2, 013297 (2020)
[7] N. Cherroret, V. Josse, Ondes et désordre, «Atomes, ions, molécules ultra-froids. Applications aux technologies quantiques«, Editions EDP Sciences

CONFOcaL is a theoretical physics project aiming to explore the properties of disordered fluids of light. Fluids of light constitute novel and flexible systems of effectively interacting photons that exhibit many fascinating properties of quantum gases. This topic falls in line with a strong scientific activity in the field of cold atomic gases, but it addresses these questions from the original perspective of optics.

The project relies on three core objectives. First, we propose to study how effective photon interactions – which may give rise to light superfluidity – in an optical beam compete with "mesoscopic" phenomena due to coherent multiple scattering of light in disorder, like Anderson localization or coherent backscattering. Second, we aim to describe the mechanisms allowing or preventing a disordered fluid of light to thermalize or even to "condense" due to photon interactions. In particular, the possibility of a photonic Kosterlitz-Thouless transition will be explored. Last, we propose an investigation of localization phenomena in disordered optical beams subjected to gauge fields realizing either a spin-orbit coupling or a magnetic field for the photons. So far, all these questions have been little, if not at all addressed.

The project has a strong interdisciplinary character, at the crossroads of the physics of quantum gases, disordered systems and nonlinear optics. We believe that this interdisciplinarity is the promise of a rich physics, with potentially a significant impact on the research in these fields. CONFOcaL primarily aims to boost the fundamental understanding of disordered fluids of light, but also to accompany the rapidly growing experimental activity in this recent field. In this context, the project will involve strong collaborations with French experimental groups at Institut de Physique de Nice and at Laboratoire Kastler Brossel in Paris.

CONFOcaL will be competitive on international stage, as it will benefit from the expertise of the coordinator and his research team in the fields of interacting quantum gases and disordered systems. It will also involve the organization of scientific events supported by the CNRS groupement de recherche "Contrôle des Ondes en Milieu comPLEXE" directed by the coordinator since 2018.