Optical preparation and detection of spin coherence in molecules and crystal defects

This thesis focuses on theoretical and experimental studies of optical preparation and detection of electron spin coherence in molecules and crystal defects. First, a detailed analysis is presented of how a gradual symmetry distortion leads to a complete alteration of optical selection rules for the hydrogen atom (Chapter 2). It is then investigated how the Time-Resolved Faraday Rotation (TRFR) technique allows for optical control and probing of triplet-exciton spin dynamics in metal-organic molecules by making smart use of the optical selection rules which are modified by spin-orbit coupling (Chapter 3). Subsequently, it is defined how the TRFR technique can be used to characterize spin-active color centers in materials with negligible spin-orbit coupling (Chapter 4). Finally, an experimental investigation is performed on molybdenum-impurities in silicon carbide. Here, an all-optical technique is used for characterization of the spin properties of the material. Additionally, spin qubits are brought in a superposition through so-called coherent population trapping (Chapter 5). The scientific progress of this thesis expands the range of material systems that can have functionalities in the field of quantum information based on the selective coupling of photons to electronic spin states. Moreover, it allows for a better opto-electronic characterization of these materials by providing new probing tools