Electronic structure of the neutral silicon-vacancy center in diamond

The neutrally charged silicon vacancy in diamond is a promising system for quantum technologies that combines high-efficiency optical spin initialization with long spin lifetimes (T2≈1 ms at 4 K) and up to 90% of optical emission into its 946-nm zero-phonon line. However, the electronic structure of SiV0 is poorly understood, making further exploitation difficult. Performing photoluminescence spectroscopy of SiV0 under uniaxial stress, we find the previous excited electronic structure of a single A1u3 state is incorrect, and identify instead a coupled Eu3-A2u3 system, the lower state of which has forbidden optical emission at zero stress and efficiently decreases the total emission of the defect. We propose a solution employing finite strain to define a spin-photon interface scheme using SiV0.