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Reference : UMR5221-THIGUI0-001
Workplace : MONTPELLIER
Date of publication : Monday, June 29, 2020
Scientific Responsible name : Thierry Guillet
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
The interaction between electronic excitations (excitons) and photons is strongly enhanced in optical microcavities, compared to a bulk medium. When the interaction is large enough, it can reach the strong coupling regime, where the perturbation theory isn't suitable anymore to understand the light-matter interaction. In this regime, the new eigenstates are the so-called polaritons, half exciton/half photon quasi-particles. They can be generated, transported, accumulated in dense quantum phases and brought into strong interactions. The discovery of the Bose condensation of polaritons in 2006  (at low temperature in a GaAs microcavity) has triggered many interesting research projects and led to the discovery of the superfluidity of polariton condensates, the observation of unique kinds of vortices in these “quantum fluids of light”, and the development of polaritonic devices.
GaN and ZnO-based microcavities have raised a large interest in the community thanks to their robust excitons and large oscillator strength. Indeed polariton condensates can be demonstrated at room temperature, which is a striking advantage with respect to GaAs devices operated at cryogenic temperatures. Together with our colleagues from the laboratories CRHEA, C2N and IP, our group has demonstrated in 2013 the condensation of polaritons in a ZnO microcavity at 300K  and investigated the spatial propagation of the condensates in a standard 2D cavity .
The present PhD proposal is focused on a new kind of polaritonic device: the polaritonic waveguide, i.e. an optical waveguide in which propagating photons and excitons are in the strong coupling regime. The waveguide polaritons have much longer lifetimes than cavity polaritons due to the low waveguide losses, and their investigation in GaAs is quite recent [4, 5]. Dedicated samples from CRHEA and C2N based on ZnO and GaN show that polariton lasing can be achieved in this new geometry, with the formation of new polariton condensates. We plan to control the non-linear formation of polariton condensates and associated solitonic phases in polaritonic waveguides, inspired from the atomic physics community, at the frontier between non-linear optics, quantum optics and condensate physics.
The candidate should have a strong background (master degree) in semiconductor physics and/or quantum optics, optical spectroscopy, non-linear optics.
 Kasprzak, J. et al. Bose-Einstein condensation of exciton polaritons. Nature 443, 409–414 (2006).
 Li, F. et al. From Excitonic to Photonic Polariton Condensate in a ZnO-Based Microcavity. Phys Rev Lett 110, 196406– (2013).
 Hahe, R. et al. Interplay between tightly focused excitation and ballistic propagation of polariton condensates in a ZnO microcavity. Phys. Rev. B 92, 235308 (2015).
 Walker, P. M. et al. Ultra-low-power hybrid light–matter solitons. Nat. Commun. 6, 8317 (2015).
 Brimont et al., Strong coupling of exciton-polaritons in a bulk GaN planar waveguide: quantifiying the Rabi splitting, arXiv:2002.05066, and submitted (2020)
The thesis will take place in the team OECS (Optics of collective states and spins), axis PEPS, of the Laboratory Charles Coulomb (L2C). We have developed a broad expertise in the field of light-matter coupling in wide bandgap semiconductors, from polariton physics in GaN and ZnO microcavities to photonic crystals, microdisks, and microlasers from the blue to the UV spectral range. Three experimental platforms are dedicated to wide bandgap nanostructures, including a micro-spectroscopy setup specifically designed for the nonlinear spectroscopy and imaging of nitride optical resonators.
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