Mean-Field and Quantum Interactions of Strongly Confined Exciton-Polaritons

In this dissertation, we report on quantum optics experiments in a cavity quantum electrodynamics setting. In particular, we study the interactions of quantum well exciton-polaritons in hybrid dielectric-semiconductor microcavities. A carbon dioxide laser-based fabrication technique is used to create zerodimensional polariton boxes in a highly flexible fiber cavity setup at cryogenic temperatures. We verify that this approach creates strong optical mode confinement with a small confinement area effectively boosting polaritonic interactions. Using frequency- and time-domain measurements, we also report long cavity lifetimes, mainly limited by the semiconductor. The large degree of tunability of the fiber cavity setup as well as the favorable ratio of nonlinearity compared to the polariton decay rate allows us to investigate different scenarios: Upon tuning the experimental parameters, we can go from a regime with vanishing polariton interactions and negligible quantum fluctuations to one where quantum fluctuations are the dominant source of noise. Photon correlation measurements are established as a tool to measure the Liouvillian eigenspectrum dictating the dynamics of the driven-dissipative system over this whole range. Approaching the thermodynamic limit with diverging particle number, we demonstrate the critical slowing down of the system dynamics by more than nine orders of magnitude compared to the intrinsic decay rate as it undergoes a first-order dissipative phase transition (DPT). Exploring the opposite regime, we show photon correlation measurements under weak excitation. An upconversion-based setup is employed to ensure a time resolution sufficient to measure single-particle dynamics. The observed antibunching is a genuinely-quantum manifestation of exciton-polaritons establishing the onset of single-particle properties. We report an unexpected long-lived photon bunching superposing these results which we attribute to a thermal bath of localized excitons feeding back into the cavity.