Resonant optical spin initialization and readout of single silicon vacancies in silicon carbide

The silicon mono-vacancy defect in 4H-SiC is a promising candidate for solid-state quantum information processing. Recent high-resolution resonant optical spectroscopy on single defects have shown favorable low temperature optical properties, i.e., two narrow and nearly lifetime-limited optical transitions with no discernable zero-field splitting fluctuations or spectral diffusion. We present a theoretical fine structure model that describes the energy level structure and reveals all intersystem crossing and spin polarization time constants of the V2 defect, shedding light on its optical and spin characteristics. In particular, we show that the silicon mono-vacancy is described well by a four-level optical structure assisted by additional non-radiative transitions leading to rich dynamical spin pumping behavior. Our calculated rates result in an overall fluorescence lifetime of 5.8 ns in good agreement with measurements. Based on this model, we show that initialization fidelities exceeding 99% are theoretically attainable at low resonant laser powers. Further, we describe the differences in optical properties between the cubic and the hexagonal defect sites due to dynamic and pseudo Jahn-Teller effects.