  Single-photon emitters play an essential role in quantum technologies,
including quantum computing and quantum communications. Atomic defects in
hexagonal boron nitride (h-BN) have recently emerged as new room-temperature
single-photon emitters in solid-state systems, but the development of scalable
and tunable h-BN single-photon emitters requires external methods that can
control the emission energy of individual defects. Here, by fabricating van der
Waals heterostructures of h-BN and graphene, we demonstrate the electrical
control of single-photon emission from atomic defects in h-BN via the Stark
effect. By applying an out-of-plane electric field through graphene gates, we
observed Stark shifts as large as 5.4 nm per GV/m. The Stark shift generated
upon a vertical electric field suggests the existence of out-of-plane dipole
moments associated with atomic defect emitters, which is supported by
first-principles theoretical calculations. Furthermore, we found field-induced
discrete modification and stabilization of emission intensity, which were
reversibly controllable with an external electric field.
