A stable, single-photon emitter in a thin organic crystal for application to quantum-photonic devices

Single organic molecules offer great promise as bright, reliable sources of identical single photons on demand, capable of integration into solid-state devices. It has been proposed that such molecules in a crystalline organic matrix might be placed close to an optical waveguide for this purpose, but so far there have been no demonstrations of sufficiently thin crystals, with a controlled concentration of suitable dopant molecules. Here we present a method for growing very thin anthracene crystals from super-saturated vapour, which produces crystals of extreme flatness and controlled thickness. We show how this crystal can be doped with a widely adjustable concentration of dibenzoterrylene (DBT) molecules and we examine the optical properties of these molecules to demonstrate their suitability as quantum emitters in nanophotonic devices. Our measurements show that the molecules are available in the crystal as single quantum emitters, with a well-defined polarisation relative to the crystal axes, making them amenable to alignment with optical nanostructures. We find that the radiative lifetime and saturation intensity vary little within the crystal and are not in any way compromised by the unusual matrix environment. We show that a large fraction of these emitters are able to deliver more than $10^{12}$ photons without photo-bleaching, making them suitable for real applications.Comment: 12 pages, 10 figures, comments welcom

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

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.Open Acces

Differential regulation of local mRNA dynamics and translation following long-term potentiation and depression

Decades of work have demonstrated that mRNAs are localized and translated within neuronal dendrites and axons to provide proteins for remodeling and maintaining growth cones or synapses. It remains unknown, however, whether specific forms of plasticity differentially regulate the dynamics and translation of individual mRNA species. To address these issues, we targeted three individual synaptically-localized mRNAs, CamkIIa, Beta actin, Psd95, and used molecular beacons to track endogenous mRNA movements and reporters and Crispr-Cas9 gene editing to track their translation. We found widespread alterations in mRNA behavior during two forms of synaptic plasticity, long-term potentiation (LTP) and depression (LTD). Changes in mRNA dynamics following plasticity resulted in an enrichment of mRNA in the vicinity of dendritic spines. Both the reporters and tagging of endogenous proteins revealed the transcript-specific stimulation of protein synthesis following LTP or LTD. The plasticity-induced enrichment of mRNA near synapses could be uncoupled from its translational status. The enrichment of mRNA in the proximity of spines allows for localized signaling pathways to decode plasticity milieus and stimulate a specific translational profile, resulting in a customized remodeling of the synaptic proteome