Confocal microscopy for T centres in silicon

Spin defects in silicon boast long lifetimes and potential scalability with existing nanofabrication foundry processes. Paired with silicon photonics, optically active spin defects offer a path to scalable optically interfaced quantum technologies, such as quantum communication networks and optically coupled qubits. The T centre in silicon is a paramagnetic radiation damage centre that is optically active in the telecommunication O-band, making it a strong candidate for spin-photon interfaces. Certain single-photon based quantum technologies rely on the production of indistinguishable photons, a characteristic which may be found from an optical centre’s zero-phonon line. In this study we measure the zero-phonon line fraction of the T centre in silicon-28 at 4.2 K to be 22.9 ± 0.2%. Isolating optical defects in silicon is difficult due to the relatively low radiative efficiencies of silicon-based emitters and silicon’s large refractive index (n ≈ 3.5), trapping light by total internal reflection. Estimates using bound exciton ground state lifetime measurements from previous studies suggest isolation and measurement of single T centres is possible by confocal microscopy. We develop a confocal microscope system designed for measuring photoluminescence from cryogenically cooled silicon and characterize its resolution performance in reflection and above-band photoluminescence. Silicon photonic ‘micropuck’ structures were designed and fabricated to increase collection efficiency from single T centres into a microscope objective.