47th Vietnam Conference on Theoretical Physics (VCTP47)
Hội nghị Vật lý lý thuyết Việt Nam lần thứ 47
Tuy Hòa, 14 August 2022

ProgrammeI.6  Invited, VCTP47 Date: Monday, 1 August 2022 Time: 16:30  17:00 Online presentation Strong coupling regime between a nonHermitian topological charge and excitons in semiconductorHai Son Nguyen (1,2) (1) Univ Lyon, Ecole Centrale de Lyon, CNRS, INSA Lyon, Université Claude Bernard Lyon 1, CPE Lyon, CNRS, INL, UMR5270, Ecully 69130, France (2) Institut Universitaire de France (IUF), Paris, France Nonperturbative radiationmatter coupling between dipoleactive material excitations and
confined modes of the electromagnetic field leads to the concept of polaritons, i.e., hybrid excitations of
mixed nature involving at least two fields with different characteristics [1]. Excitonpolaritons, in
particular, are mixed lightmatter excitations resulting from the strong coupling regime between exciton
in semiconductors and confined photons. Harnessing these hybrid excitations provides a rich playground
to explore fascinating fundamental features, as outofequilibrium BoseEinstein condensation and
quantum fluids of light, plus novel mechanisms to be exploited in optoelectronic devices.
In this talk, I will present the theory and experimental realizations of the strong coupling regime
between excitons in quantum wells and a peculiar confined photon state called Bound state In a
Continuum (BIC). BICs are peculiar localized states that are forbidden to radiate despite lying in a
continuum of propagating waves [2]. These states were first predicted by Von Neumann and Wigner in
1929, and were once regarded as an “exotic” quantum mechanical effect. The origin of BICs is nowadays
fully unraveled as a particular solution of wave equations, which has led to their exploitation in other
fields where it is straightforwardly attributed to destructive interference mechanisms or symmetry
mismatches. Interestingly, each photonic BIC in an optical lattice is attributed to a topological charge
pinned at a polarization singularity in the momentum space [2]. This topological nature will be perfectly
transferred to the polaritonic states once the strong coupling regime is established.
As proofs of concept, I will show the experimental demonstration of a Bose Einstein
condensation in a polariton bound state in the continuum [3]. This macroscopic states has been achieved
with traditional inorganic quantum wells at cryogenic temperature. Finally, I will present the first
demonstration demonstration of polariton BIC at room temperature using hybrid organicinorganic
quantum wells [4].
Presenter: Nguyễn Hải Sơn 
Institute of Physics, VAST

Center for Theoretical Physics 
Center for Computational Physics
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