Single photon emission
from localized excitons in two-dimensional
(2D) materials has been extensively investigated because of its relevance
for quantum information applications. Prerequisites are the availability
of photons with high purity polarization and controllable polarization
orientation that can be integrated with optical cavities. Here, deformation
strain along edges of prepatterned square-shaped substrate protrusions
is exploited to induce quasi-one-dimensional (1D) localized excitons
in WSe
2
monolayers as an elegant way to get photons that
fulfill these requirements. At zero magnetic field, the emission is
linearly polarized with 95% purity because exciton states are valley
hybridized with equal shares of both valleys and predominant emission
from excitons with a dipole moment along the elongated direction.
In a strong field, one valley is favored and the linear polarization
is converted to high-purity circular polarization. This deterministic
control over polarization purity and orientation is a valuable asset
in the context of integrated quantum photonics.
Long-distance fiber-based quantum communication relies on efficient non-classical light sources operating at telecommunication wavelengths. Semiconductor quantum dots are promising candidates for on-demand generation of single photons and entangled photon pairs for such applications. However, their brightness is strongly limited due to total internal reflection at the semiconductor/vacuum interface. Here we overcome this limitation using a dielectric antenna structure. The non-classical light source consists of a gallium phosphide solid immersion lens in combination with a quantum dot nanomembrane emitting single photons in the telecom O-band. With this device, the photon extraction is strongly increased in a broad spectral range. A brightness of
17
%
(numerical aperture of 0.6) is obtained experimentally, with a single photon purity of
g
(
2
)
(
0
)
=
0.049
±
0.02
at saturation power. This brings the practical implementation of quantum communication networks one step closer.
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