Le résumé du projet de thèse est fourni en anglais.
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The formation of molecules from atoms and their interactions are among the fundamental problems of interest in a wide range of fields ranging from atomic physics to chemistry. However, experiments providing a microscopic understanding of these interactions are notoriously difficult [1]. Mimicking the behavior of atoms and molecules by many-body systems in solid-state physics and photonics has therefore become a very promising way to predict the properties of complex materials.

Polaritons, strongly coupled hybrid quasiparticles composed of excitons and photons inside a microcavity, have become a prominent model system for realizing such artificial photonic molecules. They may form a Bose-Einstein condensate-like state at higher temperatures compared to atomic systems [2]. When these condensates are placed in tailored potential landscapes, such as optically induced lattices or micropillar arrays, delocalized condensate wavefunctions arise, which are the photonic equivalent of bonding and antibonding states in molecules or band structures in lattices [3]. Due to the photonic part of the polariton wavefunction, photons leaking from the microcavity also carry the characteristic physical properties of the condensate, so they can be studied easily by means of optical spectroscopy.

The main objective of this thesis will be a joint theoretical and experimental description of the nontrivial collective states forming in polariton triads and tetrads consisting of 3 or 4 coupled micropillars, respectively [4], including the relative intensities, phases and polarizations. Especially for the triangular triads [5] the polariton state may be metastable and show temporal fluctuations. In that case, conventional interferometry is too slow to obtain reliable data, so faster spectroscopic techniques such as ultrafast homodyne detection must be applied to trace the correlations between the polariton fields in the different pillars [6,7]. One of the objectives will be to predict the bifurcation diagrams of the system and switching rates between metastable states by state-of-the-art theory.

The geometry of the micropillars also results in polarization dependent polariton tunneling rates between the individual pillars, which gives rise to an effective spin-orbit coupling [8], which results in complex pseudo-spin textures and non-trivial topological effects [9,10]. The second objective of the thesis will be therefore to study the consequence of the spin-orbit coupling in different pillar geometries.

The thesis is going to be carried out under joint supervision in University Clermont Auvergne and in TU Dortmund. The PhD student will work on the creation of theoretical models, perform numerical simulations and analyze the experimental data measured in TU Dortmund. He will also get acquainted with experimental setups and their properties during the planned secondments to TU Dortmund (approximately one half of the thesis duration).
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Début de la thèse : 01/10/2025

Funding category: Contrat doctoral

Concours pour un contrat doctoral