Manipulation and Control of Coherent States in Exciton-Polariton Systems (MacExP)

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Strong quantum coupling of excitons and photons in semiconductors results in coherent superpositions of the two components, or quasiparticles called exciton-polaritons. The appearance of such mixed modes is interesting from both the point of view of fundamental and applied research. Strong interparticle interactions result from the exciton component, while extremely low effective mass and high mobility are due to the photonic component. The field of condensation of exciton-polaritons opened up in the previous decade shortly after the demonstration of true Bose-Einstein condensates of dilute atomic gases, which opened a new chapter in the field of quantum optics. This major breakthrough on quasiparticles in solids led to a vast exploration of condensation-related phenomena and phase transitions, such as spontaneous coherence built-up, superfluidity and superconductivity. Even the use of qubits based on polariton Rabi oscillations and novel light sources emitting in the visible or terahertz (THz) range such as polariton lasers and THz bosonic lasers have been proposed. Within the last few years, a few independent efforts have been made to combine THz radiation and polariton systems in experiments, with the aim to study interaction of THz radiation and quantum-well microcavity systems. In this project, a better understanding of how THz radiation and polaritonic gases interact with each other both in the linear and nonlinear regime will be gained, which will pave the way for ultrafast manipulation and control oflight-matter coupling and the development of future practical THz-generation schemes involving polariton systems. This motivates a systematic investigation of THz-induced effects in various configurations involving ultrafast spectroscopy experiments and microcavity polaritons, which are outlined in this project. Rabi oscillations will be directly measured using a digital holography technique and the effects of transient THz pulses on the coherent state will be investigated. Time-resolved photoluminescence studies will further give access to the dynamics of polariton condensates influenced by the presence of pulsed THz radiation. Thereby, the effects of transient electric fields on condensates of polaritons, which are a unique testbed for condensation studies in solids, will be probed. In this context, light will be shed on the manipulation and control of coherent states and the ultrafast switching between a condensed and uncondensed polariton gas or a polaritonic and photonic regime will be explored. Thus, this project will deepen our understanding of phenomena related to THz-exciton-polariton coupling and enhance development at the crossroads of two disciplines with novel and sophisticated experiments, with the ultimate goal of enabling further utilization of light-matter interaction for novel optical quantum technologies and light-source concepts.