| dc.description.abstract | Cavity quantum optics deals with the interaction of photons and molecules inside an optical cavity, i.e., in the region between two closely spaced mirrors. Perfect optical cavities can only support certain frequencies of light. In addition, the intensity of the light matter interaction is enhanced by the confinement. This leads to profound changes in chemical reactivity when molecules are placed inside an optical cavity. Possible examples of the field-induced modifications include alteration of absorption and emission spectra as well as the possibility to fine tune the rates of both photochemical and thermal reactions. The recent difficulties in reproducing the experimental evidence, however, underline the critical role played by a solid theoretical understanding of the strong coupling regime to advance this research area. In this thesis we introduce new theoretical tools to gain insight into the complex interplay between light and matter, namely molecular orbitals. These mathematical objects visually show how the spatial distribution of each electron in the molecule changes due to the cavity. They are therefore perfectly suited to illustrate how the field affects reactivity. Additionally, perturbative approaches are introduced to further enhance our understanding of electron-photon correlation. While numerous experimental applications of the light-matter interaction have already been proposed, computational studies provide a prime position to investigate and propose new applications and phenomena. This thesis specifically deals with ionization in optical cavities and strong coupling to circularly polarized fields. Ionization is a very well known phenomenon that plays a critical role in X ray spectroscopies as well as in initiating highly energetic reactive pathways. Confining the free electrons in a resonator grants significant control over the electron removal process with the possibility to significantly reduce the ionization barrier. This result opens the way to the engineering of tunable X-ray spectroscopies in optical devices as well as cavity modulated hot electron injections. Circularly polarized fields can differentiate between the two mirror images of a chiral molecule due to their circular dichroism. As a result, the energy degeneracy between the enantiomers is lifted inside a chiral cavity. This observation suggests that strong coupling to circularly polarized fields can be used to separate enantiomers or even better to induce enantioselectivity in reactions that are usually non selective. The magnitude of the cavity effects is linked to how small the quantization volume of the field is. While strong coupling is routinely achieved in optical cavities, larger light matter coupling strength, i.e. smaller quantization volumes, can be achieved using plasmonic nanoparticles. The chiro-optical effects of nanoparticle structures are, however, linked to the simultaneous interaction of multiple plasmons, which makes the theoretical modeling of the property numerically challenging. A new effective-field methodology is therefore introduced to account for multimode effects in computationally efficient way. | en_US |
