Quantum bit with telecom wave-length emission from a simple defect in Si

Defect-related spin-to-photon interfaces in silicon promise the realization of quantum repeaters by combining advanced semiconductor and photonics technologies. Recently, controlled creation/erasure of simple carbon interstitial defects have been successfully realised in silicon. This defect has a stable structure near room temperature and coherently emits in the wave-length where the signal loss is minimal in optical fibres used in communication technologies. Our in-depth theoretical characterization confirms the assignment of the observed emission to the neutral charge state of this defect, as arising due to the recombination of a bound exciton. We also identified a metastable triplet state that could be applied as a quantum memory. Based on the analysis of the electronic structure of the defect and its similarities to a known optically detected magnetic resonance centre in silicon, we propose that a carbon interstitial can act as a quantum bit and may realize a spin-to-photon interface in complementary metal-oxide semiconductor-compatible platforms. This work presents a theoretical investigation of the single carbon interstitial (Ci) defect in silicon as a potential candidate for spin-photon interfaces. Computed charge transition levels and optical properties show good agreement with the experimental results and allow assigning the experimentally observed telecom zero-phonon emission (1448 nm) to the neutral Ci defect.