Controlled excitation of quantum emitters by nonlinear plasmonic nearfields

• Applicant: Professor Dr. Markus Lippitz
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 415999345

Even in the focus of the best microscope objective the optical field resembles a plane wave with a spatially flat wave front. This makes the dipole approximation ubiquitous when modelling the interaction of molecules, quantum dots and proteins with light. Effects beyond this approximation, for example different optical selection rules, are accessible only with optical fields that are curved on a sub-wavelength length scale. Plasmonics is able to generate such sculptured fields by elaborate arrangements of metallic nanostructures. However, the spatial shape of the optical field is rather fixed, as it is defined by the material. This makes it difficult to switch the spatial shape, for example to demonstrate its influence on the excitation spectrum of a large multi-chromophoric system.In this project we propose to use nonlinear plasmonics to overcome this limitation. Nonlinear effects such as third-harmonic generation are boosted by the field enhancement inside plasmonic nanos-tructures. While linear plasmonics is rather well understood, in nonlinear plasmonics still many questions are open. This project contributes to two key questions: How is third-harmonic generation in noble metals connected to the electronic band structure and the occupation function? The answer to this question will allow us to tune the local nonlinear response by, e.g. locally heating the electron gas. The second topic are hybrid nonlinear plasmonic structures in which the locally generated third harmonic will be used to excite single quantum emitters. In combination, our plasmonic nanostructure will act as light source with a spatial arrangement that is controllable on a sub-wavelength length scale by a tailored nonlinearity. We envision placing large multichromophoric systems with spatially extended excited states near this light source, such as light-harvesting complexes or H aggregates. Our novel light source will allow spectroscopy beyond the dipole approximation which we expect to shed light on, e.g. the role of quantum coherence in biological systems.

• DFG Programme: Research Grants