High-purity and stable single-photon emission in bilayer WSe$_2$ via phonon-assisted excitation

Abstract: The excitation scheme is essential for single-photon sources, as it governs exciton preparation, decay dynamics, and the spectral diffusion of emitted photons. While phonon-assisted excitation has shown promise in other quantum emitter platforms, its proper implementation and systematic comparison with alternative excitation schemes have not yet been demonstrated in transition metal dichalcogenide (TMD) quantum emitters. Here, we investigate the impact of various optical excitation strategies on the single-photon emission properties of bilayer WSe$_2$ quantum emitters. Based on our theoretical predictions for the exciton preparation fidelity, we compare excitation via the longitudinal acoustic and breathing phonon modes to conventional above-band and near-resonance excitations. Under acoustic phonon-assisted excitation, we achieve narrow single-photon emission with a reduced spectral diffusion of 0.0129 nm, a 1.8-fold improvement over above-band excitation. Additionally, excitation through breathing-phonon mode yields a high purity of $ 0.947\pm 0.079\,$ and reduces the decay time by over an order of magnitude, reaching $(1.33 \pm 0.04)\,$ns. Our comprehensive study demonstrates the crucial role of phonon-assisted excitation in optimizing the performance of WSe$_2$-based quantum emitters, providing valuable insights for the development of single-photon sources for quantum photonics applications.