Dark excitons and dark polaritons in hybrid perovskites.*

 Dark optical processes are often elusive and difficult to quantify. In my talk, I will discuss how exciton/exciton scattering within the manifold of dark (i.e., non-optical) states leads to tell-tale signatures in the non-linear optical response of low-dimensional semiconductors and polariton forming microcavity systems. Our theoretical approach is based on a non-equilibrium/non-stationary stochastic model derived from a composite-boson treatment of electron/hole excitations, allowing us to compute their non-linear coherent optical responses.  We shall also discuss how correlated noise can affect the decoherence and fidelity of a quantum state. While the talk will focus on 2D lead-halide perovskite semiconductors, I will make contact with recent experiments of the Silva group in which these materials are embedded in a polaritonic microcavity.