Thesis defense of Carolin Lüders

For quantum technology, hybrid systems are needed to connect different physical systems, e.g. a matter system for information processing and light for communication. For connecting semiconductors and light, semiconductor quantum optics investigates how light influences the quantum state of the semiconductor and how the state of the semiconductor can be measured via the emitted light. To measure the quantum state of light, optical homodyne tomography (OHT) is a versatile technique that is widely applied in quantum optics. But its application to semiconductor emission is often prevented by the lack of a fixed phase reference for nonresonant luminescence and by the fast time scales of the system. These challenges are tackled in this work. We present the application of OHT to semiconductor luminescence without a fixed phase reference in order to investigate coherence properties and the quantum state. Thereby, a pulsed local oscillator and fast detectors enable a high time resolution. As a testbed for the method, we investigate the emission from an exciton-polariton condensate in a GaAs microcavity. Specifically, this work shows which information can be gained by using one, two and three homodyne detection channels. With one channel, the second-order photon correlation function g(2)(0) is measured. Via two channels, we measure the phase-averaged Husimi function and quantify the amount of quantum coherence in the polariton system. With three channels, we reconstruct the regularized P function, depending on postselected initial conditions, and track the temporal decay of quantum coherence.

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