On-chip control of light emission by single-photon sources


Single photons are a useful tool that facilitates the exploitation of quantum effects that prove useful for overcoming the constraints of classical physics, whether this is improving the precision for metrology, or solving the classically unsolvable problems using novel quantum information processing techniques. InAs/GaAs quantum dots (QDs) are one of the leading sources for the generation of single-photons in the solid-state, offering relatively easy fabrication of complex photonic structures, integration with electronics, and offering high quality single-photon emission. However, they are not without issue, for example, QDs while having theoretical GHz emission rates are impacted by the limited extraction efficiency imposed by high refractive index contrasts at the material free-space interface causing total internal reflection, which reduces the effectiveness in applications that requires guaranteed emission of single-photons, or high single-photon flux. In this thesis, we discuss various applications of hybrid photonic devices, and techniques which can be applied to fabricate devices that enable control of the emission of single photons generated by InAs/GaAs QDs. We present simulations and experimental results of several alternative nanophotonic devices that are based on a simple metallic nano-ring deposited on the surface, that focuses the emission for enhanced free-space collection. When combined with a metallic back-reflector below the substrate, made possible using a novel manual thermal release adhesive tape assisted membrane transfer technique, we show an average increase in single-photon emission brightness by about 7.5×, referenced to a device with only a back reflector, comparing emitters within and outside the nano-rings, with collected photon rates as high as 7 million photons per second, and enhancements over a 60nm bandwidth. The intrinsically broadband nature of the devices we present do not require bespoke optimisation and subsequent tuning to individual emitters, as is the case with most optical cavity based geometries currently used for bright and indistinguishable photons, which along with the ease of fabrication, and compatibility with any emitter and substrate, improves scalability and yield. Furthermore, the introduction of metal paves the way for their use as electrical contacts to apply localised electric fields for carrier injection or wavelength tuning. Additionally, we show how a considered approach to the design of the epitaxial layers of the QD membranes could be used to further optimise the coupling to free-space, or result in a reduction of the radiative lifetime of emitters, potentially leading to improved coherence, with simulated results giving over 285× enhancement compared to unprocessed material. Finally, we further show advantage of our planar geometry by fabricating vertical polymer nanowires above the metallic nano-rings. The nanowires guide single photons into a mode that is suitable for collection with small numeral apertures, such as single mode fibres

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