Long optical coherence times of shallow-implanted, negatively charged silicon vacancy centers in diamond

The creation of single, negatively charged silicon vacancy (⁠$SiV−$⁠) centers in well-defined diamond layers close to the host surface is a crucial step for the development of diamond-based quantum optic devices with many applications in nanophotonics, quantum sensing, or quantum information science. Here, we report on the creation of shallow (10 nm below the surface), single $SiV−$ centers in diamond using low energy $Si+$ ion implantation with subsequent high temperature annealing at 1500 °C. We show transition linewidths down to 99 MHz and narrow inhomogeneous distributions. Furthermore, we achieved a reduction of homogeneous linewidths by a factor of 2 after removing subsurface damage using oxygen plasma processing. These results not only give insights into the formation process of $SiV−$ centers but also indicate a favorable processing method to fabricate shallow single quantum emitters in diamond perfectly suited for coupling to nanostructures on the diamond surface.