Exciton-polaritons are 2D light-matter excitations in microcavities with embedded quantum wells which have been extensively studied for macroscopic quantum phenomena like Bose-Einstein condensation, superfluidity, vortices, and solitons to name a few. In this Midterm Seminar, I will present the series of experiments on exciton-polaritons that we have done during my PhD candidature and the future directions we are looking into.
Firstly, we will discuss exciton-polariton condensation in an optically induced potential. With fine control over the pumping spatial profile, we were able to create a billiard or resonator on the plane of the quantum wells and demonstrate the existence of the non-Hermitian (exceptional point) and Hermitian (diabolical point) degeneracies by looking at their associated topological Berry phase [1,2].
We will also discuss experiments on loading of exciton-polariton condensates in a 1D periodic potential made of arrays of mesas buried in the microcavity. By changing the power and spatial profile of the optical pump, we were able to load the condensate into different states of the periodic band structure . In cases where the condensate occupy a high energy gap state, we observe a near-field interference pattern called the Talbot effect  away from the 1D array. Its nontrivial pattern leads us to conclude that we were able to create a 1D phase grating for exciton polaritons.
Finally, we will present recent experimental results on single-shot imaging of exciton-polariton condensation in a planar microcavity with Gaussian and ring pump profile. To the best of our knowledge, this is the first time that a single realization of a polariton condensate is imaged in clean inorganic microcavities that may reveal interesting dynamics of nonequilibrium Bose–Einstein condensation and Berezinskii–Kosterlitz–Thouless transition.
 T. Gao et al, Nature 526, 554–558 (2015).
 E. Estrecho et al, arXiv:1607.05805
 K. Winkler et al, Phys. Rev. B 93, 121303(R) (2016)
 T. Gao et al, Phys. Rev. Lett. 117, 097403 (2016)