Photon emitters in hexagonal boron nitride: creating, enhancing, and controlling optically active colour centres

Hekmati, Reza 2023. Photon emitters in hexagonal boron nitride: creating, enhancing, and controlling optically active colour centres. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

In this thesis, I study photon emitters in hBN to create and control optically active colour centres. In addition, enhancing the coupling efficiency of a quantum emitter into an objective lens is studied. I present a step-by-step method for designing a bullseye Bragg grating structure to enhance the collection efficiency and increase the Purcell factor. In my design, I explore the coupling condition between the dipole and the cavity and show that the collection efficiency remains high because of exploiting a gold layer as a reflector layer. I calculate the coupling efficiency between the dipole and the cavity. I apply apodization to the grating in the bullseye structure to achieve higher collection efficiency. I investigate different approaches, including treatment, local strain using nanostubs, annealing and ion irradiation to generate defect centres in hBN. I use a combination of strain and plasma/annealing treatment to generate reproducible defect centres in hBN. I discovered that consecutive annealings at medium temperature on a single flake could create ensembles of defects, while single annealing at high temperatures could create narrower linewidth defects, that some of them showed power saturation behaviours. I investigate fluence and ion energy for Kr+ irradiated sample. My studies show that the fluence of 10^12 cm^-2 with an ion energy of 150-200 eV can create single defect-like emitters. Subsequent annealing on these samples showed one sign of a narrow linewidth emitter in the highest energy sample. Moreover, we investigate the electron spin properties of VB- centres in ensembles of defects in a C-implanted hBN sample. We report that the dephasing time of the Rabi oscillation and Ramsey interferometry at 90 mT are around 30 ns and 3 ns, respectively. We apply the spin-echo sequence to the VB- centres and achieve a spin-echo coherence time of 100 ns at 90 mT.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	2D material, hexagonal boron nitride, spin qubit, color centre, bullseye cavity structure
Funders:	Cardiff University
Date of First Compliant Deposit:	30 March 2023
Last Modified:	05 Apr 2023 09:55
URI:	https://orca.cardiff.ac.uk/id/eprint/158238

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