  Resonant excitation of solid-state quantum emitters enables coherent control
of quantum states and generation of coherent single photons, which are required
for scalable quantum photonics applications. However, these systems can often
decay to one or more intermediate dark states or spectrally jump, resulting in
the lack of photons on resonance. Here, we present an optical co-excitation
scheme which uses a weak non-resonant laser to reduce transitions to a dark
state and amplify the photoluminescence from quantum emitters in hexagonal
boron nitride (hBN). Utilizing a two-laser repumping scheme, we achieve
optically stable resonance fluorescence of hBN emitters and an overall increase
of ON time by an order of magnitude compared to only resonant excitation. Our
results are important for the deployment of atom-like defects in hBN as
reliable building blocks for quantum photonic applications.
