While many defects in silicon provide long-lived spin qubits, it remains difficult to use them as the base for a spin-photon interface, because many have no optical transition at all, and those which do typically suffer from poor radiative efficiencies or have inconvenient optical transition energies. A number of silicon defects with transition wavelengths in the telecommunication bands are already known to exist, prominently from the set of centres known as radiation damage centres, produced when exposing the silicon lattice to radiation damage. Of special interest is the T centre, a paramagnetic defect thought to be made of two carbon atoms and one hydrogen atom. The ground state of the neutral defect has an uncoupled electron spin, and the bound exciton associated with the centre has a strong luminescence transition at 1326 nm. In this first study of T centres in 28Si, we revealed the expected but nonetheless remarkable linewidth improvement over natural Si due to the removal of isotopic broadening, which provides an improved bound on the true single-centre linewidth in natural Si. From pulsed laser transient spectroscopy, we measured a lifetime of 0.94(1) μs for the bound exciton state. Using photoluminescence excitation techniques, we attributed the dominant broadening mechanism to thermal excitations to a higher excited state and showed that resonant optical saturation of the transition results in a dipole moment of 0.27(3) Debye and a radiative efficiency of 13(4) %. We also estimated the T centre concentration of one sample from its absorption spectrum, and gave energy values for a series of transitions to higher energy excitonic states. Furthermore, experiments with an external magnetic field confirmed that the excited state Zeeman splitting is anisotropic and reveal that the ground state electron has an anisotropic hyperfine interaction with the hydrogen atom with a coupling constant on the order of 3 MHz. We demonstrated that initialization, readout and control over both the electron spin and the nuclear spin are possible using optical excitation and magnetic resonance, and measured T1 relaxation times greater than 16 s as well as T2 coherence times of 2.1(1) ms for the electron spin and 1.1(2) s for the hydrogen nuclear spin.
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Thesis advisor: Simmons, Stephanie
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