Another research direction we pursue focuses on trion-polaritons, a bound 4-body complex consisting of a hole, two electrons and a photon. These particles are the optical excitations of a low density 2DES strongly coupled to a cavity mode. Until now, trions have been observed in the optical spectra of 2DES, carbon nanotubes and more recently in transition metal dichalcogenides. Variational calculus suggests that the 2D trion can be approximated by two electrons orbiting a fixed hole, with one of the electrons having a larger Bohr radius. Recent theoretical and experimental investigations suggests that by coupling the trions to a two-dimensional cavity mode, trion-polaritons can be formed. Furthermore, the competition between the Coulomb interaction and light matter coupling determines the spin properties of the trion-polaritons. In a joint work with C. Ciuti, we address is the strength of polariton-polariton interactions and their enhancement by coupling to a 2DES.