  Strong light matter coupling between excitons and microcavity photons, as
described in the framework of cavity quantum electrodynamics, leads to the
hybridization of light and matter excitations. The regime of collective strong
coupling arises, when various excitations from different host media are
strongly coupled to the same optical resonance. This leads to a
well-controllable admixture of various matter components in three hybrid
polariton modes. Here, we study a cavity device with four embedded GaAs quantum
wells hosting excitons that are spectrally matched to the A-valley exciton
resonance of a MoSe2 monolayer. The formation of hybrid polariton modes is
evidenced in momentum resolved photoluminescence and reflectivity studies. We
describe the energy and k-vector distribution of exciton-polaritons along the
hybrid modes by a thermodynamic model, which yields a very good agreement with
the experiment.
