Coupling of single organic molecules to photonic micro-structures

Abstract

Dopant molecules in organic crystals can be triggered to create single photons with certainty. This basic principle is currently being leveraged to develop a new generation of photonic components capable of delivering single photons to optical hardware. In turn, these single-photon sources are enabling increasingly sophisticated technologies based on the quantum nature of photons, in areas such as quantum computation and quantum cryptography. In this thesis, I present my work towards realising an organic single-photon source using dibenzoterrylene (DBT) molecules in anthracene crystals. To realise a deterministic single-photon source with molecules, we have to address two main challenges. First, it is necessary to collect all the photons emitted by a single molecule into a propagating optical mode. To achieve this, I have investigated methods to place single DBT molecules close to the field maximum of single-mode waveguides. I describe our strategy which consists of overlaying microfluidic channels on top of silicon-nitride ridge waveguides. With this geometry, targeted crystallisation of DBT-doped anthracene occurs in small gaps running across the waveguides. We probe the system using coherent single-molecule spectroscopy and estimate that 7% of the molecular emission is coupled to the waveguide modes for one of our fabricated devices. The second challenge is to turn DBT molecules into coherent two-level systems. The vibrational spectrum of DBT prevents the system from generating indistinguishable single-photons without filtering of the emission. However, the reduction in single-photon efficiency due to filtering can be improved by selectively accelerating the radiative decay of the zero-phonon line. I discuss how such an enhancement is possible using optical cavities and how both challenges can be addressed with this approach. Finally, I introduce a new design for a vertically-emitting cavity with an active layer of DBT-doped anthracene.