  Semiconductor quantum dots have emerged as promising candidates for
implementation of quantum information processing since they allow for a quantum
interface between stationary spin qubits and propagating single photons. In the
meanwhile, transition metal dichalcogenide (TMD) monolayers have moved to the
forefront of solid-state research due to their unique band structure featuring
a large band gap with degenerate valleys and non-zero Berry curvature. Here we
report the observation of quantum dots in monolayer tungsten-diselenide with an
energy that is 20 to 100 meV lower than that of two dimensional excitons.
Photon antibunching in second-order photon correlations unequivocally
demonstrates the zero-dimensional anharmonic nature of these quantum emitters.
The strong anisotropic magnetic response of the spatially localized emission
peaks strongly indicates that radiative recombination stems from localized
excitons that inherit their electronic properties from the host TMD. The large
$\sim$ 1 meV zero-field splitting shows that the quantum dots have singlet
ground states and an anisotropic confinement most likely induced by impurities
or defects in the host TMD. Electrical control in van der Waals
heterostructures and robust spin-valley degree of freedom render TMD quantum
dots promising for quantum information processing.
