Brightening of Optical Forbidden Interlayer Quantum Emitters in WSe₂ Homobilayers

Interlayer excitons (IXs) in layered van der Waals materials are promising for quantum technologies and fundamental studies such as exciton-polariton condensation due to their large permanent dipole moments. However, their indirect bandgap optical transition through the Q-K channel renders them momentum forbidden and thus less relevant for optical applications. Here, we demonstrate a method for brightening momentum indirect Q-K transitions from IX quantum emitters (QEs) in 2H-stacked bilayer WSe₂ by simultaneously employing local strain and plasmonic nanocavity coupling. Initially, long T₁ lifetimes up to 140 ns are indicative of momentum indirect transitions. Magneto-photoluminescence data show a striking bimodal distribution of g-factors between mono- and bilayer QEs, with a well-defined value of g = 9.5 for IX, highlighting their momentum indirect nature and decoupling from local strain variations. In addition, angle-resolved PL measurements reveal that local curvature on the nanostressor induces a dipole orientation tilt of the QEs, affecting cavity coupling. By embedding these strained QEs into plasmonic cavities, we achieve a 10-fold increase in emission intensity and a 24-fold enhancement in the T₁ lifetime in the best case (12-fold average), leading to bright single-photon emission rates up to 1.45 ± 0.1 MHz into the first lens. Moreover, the demonstrated brightening of IX transitions allowed to push the emission wavelength reliably to around 810 nm that enables free-space quantum optical communication.