Preparation and testing of organic dye molecules as single photon sources on a chip

Abstract

The physical realisation of a photonic quantum computer requires a reliable, fast, ondemand source of single indistinguishable photons. A promising candidate for one of these sources is a single dye molecule in a solid state matrix placed within the evanescent field of a photonic waveguide. This thesis explores the possibility of coupling of single dibenzoterrylene (DBT) molecules in an anthracene matrix to a silicon nitride waveguide at room temperature. I first discuss the theory by which photons from a DBT molecule can be evanescently coupled to a ridge waveguide. I present a novel growth method to form DBT-doped anthracene crystals which is very promising for applications to photonic devices. I discuss the methodology and the theory of such growth. I describe the confocal microscope I developed and used to image and characterise the emission of the single DBT molecules embedded in these crystals. My measurements show that the molecules are extremely stable single quantum emitters with a well-de ned polarization relative to the crystal axes. Measurements of the saturation intensity at room temperature allow me to estimate that a single DBT molecule could deliver at least 1012 photons before bleaching. This method of growth was used to deposit DBT molecules on top of a silicon nitride ridge waveguide. The results of the coupling experiment are shown. These include confocal images, saturation and lifetime measurements. The coupling efficiency is calculated and compared to what was simulated. The challenges of such structures are then presented. To tackle these challenges I deposited the molecules on top of lithium niobate and in silicon nitride slots. I conclude with a proposal for constructing the best photonic structure which would guarantee an easy deposition of the molecules and high coupling efficiencies.