  Local deformation of atomically thin van der Waals materials provides a
powerful approach to create site-controlled chip-compatible single-photon
emitters (SPEs). However, the microscopic mechanisms underlying the formation
of such strain-induced SPEs are still not fully clear, which hinders further
efforts in their deterministic integration with nanophotonic structures for
developing practical on-chip sources of quantum light. Here we investigate SPEs
with single-photon purity up to 98% created in monolayer WSe$_2$ via
nanoindentation. Using photoluminescence imaging in combination with atomic
force microscopy, we locate single-photon emitting sites on a deep
sub-wavelength spatial scale and reconstruct the details of the surrounding
local strain potential. The obtained results suggest that the origin of the
observed single-photon emission is likely related to strain-induced spectral
shift of dark excitonic states and their hybridization with localized states of
individual defects.
