  To date, quantum communication widely relies on attenuated lasers for secret
key generation. In future quantum networks fundamental limitations resulting
from their probabilistic photon distribution must be overcome by using
deterministic quantum light sources. Confined excitons in monolayers of
transition metal dichalcogenides (TMDCs) constitute an emerging type of emitter
for quantum light generation. These atomically-thin solid-state sources show
appealing prospects for large-scale and low-cost device integration, meeting
the demands of quantum information technologies. Here, we pioneer the practical
suitability of TMDC devices in quantum communication. We employ a
$\mathrm{WSe}_2$ monolayer single-photon source to emulate the BB84 protocol in
a quantum key distribution (QKD) setup and achieve click rates of up to 66.95
kHz and antibunching values down to 0.034 - a performance competitive with QKD
experiments using semiconductor quantum dots or color centers in diamond. Our
work opens the route towards wider applications of quantum information
technologies using TMDC single-photon sources.
