Nur, Salahuddin; (2018) Towards enhanced radiative emission for optical read-out of donor spins in silicon. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Silicon has several features that make it an attractive platform for implementing quantum information processing (QIP). The unique combination of a mature fabrication technology, extraordinarily long coherence times and high control fidelities of donor spins in isotopically purified silicon have made them good candidates for realising spin based quantum bits. Increased spin-photon coupling has the potential to add additional benefits including efficient optical readout of individual donor spins and even a route to generating entanglement. Efficient optical detection of the donor spin state could provide the missing piece of puzzle to realise long-range qubit couplings and construct quantum networks, however, achieving this in silicon is challenging due to its indirect bandgap. Photonic structures such as solid immersion lenses (SILs), circular Bragg resonators (CBRs), photonic crystal (PhC) cavities etc. can enhance radiative emission and/or its collection up to several orders of magnitude, potentially allowing it to compete with non-radiative processes such as Auger recombination. In this thesis, we report our first steps towards fabricating and characterizing such photonic structures, designed to enhance radiative emission and optical collection from 31P donor bound excitons (D0Xs) in silicon. We have fabricated silicon SILs using a neon focussed ion beam milling system. A bilayer resist based fabrication recipe has also been optimised using relatively inexpensive process materials, which efficiently produces CBRs and PhC cavities with desired optical properties on undoped silicon-on-insulator wafers. The optical properties of the fabricated devices are investigated using cavity reflection measurements. We have measured an absorption limited cavity quality factor (Q) of ∼ 5,000 around 31P D0X emission wavelengths (∼ 1078 nm) for silicon PhC cavities at room temperature. Silicon PhC cavities with such a quality factor (∼ 5,000) and enhanced collection can permit for optically accessing spins at a single or at least few donors level.

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