Organic nanocrystals and polymeric waveguides: a novel path towards integrated quantum nanophotonics

Single photons are very robust carriers of quantum information, making single-photon emitters a fundamental resource in a wide range of proposed photonic technologies, ranging from quantum computing and secure communication schemes to metrology applications. A fundamental step is the realization of integrated quantum photonics circuit enabling single-photon emission, logical operations, routing and detection on the same platform. In this context, hybrid systems made of molecule-based single photon sources coupled to dielectric waveguides appear as ideal candidates. In particular, single Dibenzoterrylene (DBT) molecules embedded in a crystalline matrix of Anthracene (Ac) constitute an interesting alternative to more conventional emitters - such as quantum dots or colour centers in diamonds – due to their bright, stable and narrow lifetime-limited emission at cryogenic temperatures. In this thesis, we study possible platforms to integrate single DBT molecules into dielectric waveguides and provide efficient emission and collection of single photons. As a first step we demonstrate the potentiality of an hybrid device that combines layered DBT:Ac systems and dielectric chips consisting of silicon nitride ridge waveguides and grating far-field couplers. Despite the lack of control in the positioning of the DBT molecules on the chip, we show that coupling efficiencies measured for molecules in close proximity to the dielectric waveguides are comparable to those of other solid-state systems. As a second step, we develop a simple and cost-effective fabrication method to grow Ac crystal with sub-micrometric size and tunable concentration of DBT molecules. The newly developed DBT:Ac nanocrystals, that remarkably maintain the optical properties of the bulky system at both room and cryogenic temperature, are easier to manipulate and may allow the DBT:Ac system to be fully exploited as a nanoscale single photon source. Finally we investigate the integration of DBT:Ac nanocrystals into polymers, promising materials for integrated quantum circuitry due to the broad tunability of their electro-optical and mechanical properties and their easy structuration by means of well-established lithographic fabrication methods. In particular, we demonstrate that nanocrystal-polymer composites are compatible with usual fabrication process and can be efficiently structured both in 2D and 3D. We believe that the remarkable optical properties of the developed DBT-doped organic nanocrystals and their integration in writable polymeric structures may facilitate the transition of molecules from a proof-of-concept to practical realistic applications in quantum technologies.