Brightening of Optical Forbidden Interlayer Quantum Emitters in WSe2 Homobilayers

Abstract

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.