Integrated single-molecule based single-photon sources for photonic quantum technologies

The successful development of future photonic quantum technologies heavily depends on the possibility of realizing robust and scalable nano-photonic devices. These shall include quantum emitters as on-demand single-photon sources and non-linear elements, provided their transition linewidth is broadened only by spontaneous emission. However, on-chip integration is typically detrimental for the emitter coherence properties. Moreover, conventional fabrication approaches are hardly scalable and bear limitations in terms of geometries and materials. In this thesis I present the development and realization of an alternative platform, which combines on a chip the freedom of three-dimensional polymeric architectures with the optimal properties of single photon emission from fluorescent molecules. Three-dimensional patterns are achieved via direct laser writing around selected molecular emitters, with a fast, inexpensive and scalable fabrication process. The experimental results entail deterministic positioning of the source, fabrication on different substrates (dielectric, metallic) as well as integration in suspended designs. Typical degradation affecting the photophysical properties of the emitter after nanofabrication is here avoided, and photostable close-to Fourier-limited emission from a single embedded dibenzoterrylene molecule at 3 K is demonstrated. Furthermore, enhanced light extraction is achieved in a micro-dome solid immersion lens design. In particular, the realization of the platform strongly relies on the identification of an especially suitable emitter. In this context, the simple and cost-effective reprecipitation protocol developed in our group, specifically enables fast fabrication of nanostructured anthracene (Ac) crystals with controllable concentration of dibenzoterrylene (DBT) molecules, which remarkably preserve the exeptional photophysical properties of the DBT:Ac bulk system. As described and characterized at the beginning of the thesis, this source exhibits a photostable and life-time limited single-photon emission (at cryogenic temperatures) in a nanocrystalline environment, and is hence naturally suitable to deterministic positioning and integration into photonic structures. Furthermore, featuring an appropriate combination of emission properties, this molecular single-photon source is also demonstrated to find practical application in quantum radiometry as metrology standard for photon fluxes at the low light level, for the calibration of silicon single-photon avalanche detectors. At the end of the thesis, we also investigate the possibility of handling and manipulating DBT:Ac nanocrystals for achieving deterministic positioning on silicon nitride (SiN) photonic circuits, through the patterning of a water-soluble polymer via electron-beam lithography.