  The field of quantum technology has been rapidly expanding in the past
decades, yielding numerous applications as quantum information, quantum
communication and quantum cybersecurity. The central building block for these
applications is a quantum emitter (QE), a controllable source of single photons
or photon pairs. Semiconductor QEs such as perovskite nanocrystals (PNCs) and
semiconductor quantum dots (QDs) have been demonstrated to be a promising
material for pure single-photon emission, and their hybrids with plasmonic
nanocavities may serve as sources of photon pairs. Here we have designed a
system in which individual quantum emitters and their ensembles can be traced
before, during, and after the interaction with the external plasmonic
metasurface in controllable way. Upon coupling the external plasmonic
metasurface to the array of QEs, the individual QEs switch from single-photon
to photon-pair emission mode. Remarkably, this method does not affect the
chemical structure and composition of the QEs, allowing them to return to their
initial state after decoupling from the plasmonic metasurface. By employing
this approach, we have successfully demonstrated the reversible switching of
the ensemble of individual semiconductor QEs between single-photon and photon
pair emission modes. This significantly broadens the potential applications of
semiconductor QEs in quantum technologies.
