The paper investigates the optical generation and detection of excitonic valley coherence in monolayer WSe₂. The authors establish circularly polarized optical selection rules for addressing individual valley excitons and trions, revealing coherence between valley excitons through linearly polarized luminescence. They show that linear polarization can only be generated through the recombination of an exciton in a coherent superposition of the two valleys, while the corresponding photoluminescence from trions is not linearly polarized. This demonstrates the feasibility of coherent valley manipulation using optical means, adding a critical dimension to the quantum manipulation of valley index necessary for coherent valleytronics. The study also explores the polarization dependence of valley excitons and trions, and the mechanisms of valley depolarization and decoherence. The results highlight the unique properties of monolayer WSe₂ in generating excitonic valley quantum coherence.The paper investigates the optical generation and detection of excitonic valley coherence in monolayer WSe₂. The authors establish circularly polarized optical selection rules for addressing individual valley excitons and trions, revealing coherence between valley excitons through linearly polarized luminescence. They show that linear polarization can only be generated through the recombination of an exciton in a coherent superposition of the two valleys, while the corresponding photoluminescence from trions is not linearly polarized. This demonstrates the feasibility of coherent valley manipulation using optical means, adding a critical dimension to the quantum manipulation of valley index necessary for coherent valleytronics. The study also explores the polarization dependence of valley excitons and trions, and the mechanisms of valley depolarization and decoherence. The results highlight the unique properties of monolayer WSe₂ in generating excitonic valley quantum coherence.