Single-photon emitters in WSe₂: Critical role of phonons on excitation schemes and indistinguishability

Within optical quantum information processing, single-photon sources based on a two-level system in a semiconductor material allow for on-demand generation of single photons. To initiate the spontaneous emission process, it is necessary to efficiently populate the excited state. However, reconciling the requirement for on-demand excitation with both high efficiency and high photon indistinguishability remains a challenge due to the presence of charge noise and phonon-induced decoherence in the solid-state environment. Here, we reconstruct the phonon spectral density experienced by WSe₂ quantum emitters in the emission process, and we use this information to theoretically analyze the performance of the resonant, phonon-assisted, and Swing-UP of the quantum EmitteR population (SUPER) excitation schemes. Under resonant excitation, we obtain an exciton preparation fidelity limited to 0.80 by the strong phonon coupling, which improves to 0.96 for the SUPER scheme (or 0.89, depending on the type of emitter considered). Under near-resonant phonon-assisted excitation, our theory predicts near-unity excitation fidelity up to 0.976 (0.997). Additionally, we demonstrate that, assuming the suppression of the phonon sidebands, residual dephasing mechanisms such as charge and spin fluctuations are the dominating decoherence mechanisms undermining the photon indistinguishability.