  The successful development of future photonic quantum technologies heavily
depends on the possibility of realizing robust, reliable and, crucially,
scalable nanophotonic devices. In integrated networks, quantum emitters can be
deployed as single-photon sources or non-linear optical elements, provided
their transition linewidth is broadened only by spontaneous emission. However,
conventional fabrication approaches are hardly scalable, typically detrimental
for the emitter coherence properties and bear limitations in terms of
geometries and materials. Here we introduce an alternative platform, based on
molecules embedded in polymeric photonic structures. Three-dimensional patterns
are achieved via direct laser writing around selected molecular emitters, which
preserve near-Fourier-limited fluorescence. By using an integrated polymeric
design, record-high photon fluxes from a single cold molecule are reported. The
proposed technology allows to conceive a novel class of quantum devices,
including integrated multi-photon interferometers, arrays of indistinguishable
single photon sources and hybrid electro-optical nanophotonic devices.
