Orbitally Resolved Single-Photon Emission from an Individual Atomic Vacancy Center in a Semiconductor.

Atomically confined spins are emerging as active components in quantum optoelectronic devices such as quantum bits and sensors. However, interrogating single spins at atomic length scales remains a sizable challenge, limited by diffraction in conventional optics. Here, we show that the highly local excitation provided by injecting energetic charge carriers from the atomically sharp probe of a scanning tunneling microscope can trigger single-photon emission from individual atomic vacancy centers in a layered semiconductor. With an effective spatial resolution of <1 nm, we show that the captured light closely mirrors the orbital symmetry of the bound-state wave function of the vacancy center, while photon-correlation measurements confirm single-photon emission, as reflected in clear photon antibunching signatures. Our results constitute an important step toward the realization of an electrically addressable single-atom quantum light source and solid-state spin-photon interface, addressed at the atomic scale.