  Quantum light emitters (QEs) capable of generating single photons of
well-defined circular polarization could enable non-reciprocal single photon
devices and deterministic spin-photon interfaces critical for realizing complex
quantum networks. To date, emission of such chiral quantum light has been
achieved via the application of intense external magnetic field
electrical/optical injection of spin polarized carriers/excitons, or coupling
with complex photonic/meta-structures. Here we report free-space generation of
highly chiral single photons from QEs created in monolayer WSe2 - NiPS3
heterostructures at zero external magnetic field. These QEs emit in the 760-800
nm range with a degree of circular polarization and single photon purity as
high as 0.71 and 80% respectively, independent of pump laser polarization. QEs
are deterministically created by pressing a scanning probe microscope tip into
a two-dimensional heterostructure comprising a WSe2 monolayer and a ~50 nm
thick layer of the antiferromagnetic (AFM) insulator NiPS3. Temperature
dependent magneto-photoluminescence studies indicate that the chiral quantum
light emission arises from magnetic proximity interactions between localized
excitons in the WSe2 monolayer and the out-of-plane magnetization of AFM
defects in NiPS3, both of which are co-localized by the strain field arising
from the nanoscale indentations.
