This paper investigates the quantum nature of a strongly coupled single quantum dot (QD) and cavity system, focusing on the interaction between a QD and a photonic crystal (PC) nanocavity. The authors demonstrate that the QD-cavity system exhibits quantum correlations in photoluminescence (PL) when the QD is precisely positioned at the cavity's electric field maximum. When off-resonance, photon emission from the cavity mode and QD excitons are anti-correlated at the single-photon level, confirming that the cavity mode is driven solely by the QD. When tuned into resonance, the system enters the strong-coupling regime of cavity-QED, reducing the QD lifetime by a factor of 120 and causing the photon stream from the cavity to become anti-bunched, indicating the system is in the quantum anharmonic regime. The study confirms the feasibility of achieving quantum information processing tasks in the solid state, particularly in the quantum nonlinear regime. The experimental techniques used include precise positioning of the nanocavity to a single QD, spectral tuning of the cavity mode, and measurement of quantum correlations in PL. The results provide strong evidence for the quantum nature of the QD-cavity system and support the pursuit of solid-state cavity-QED for quantum information processing.This paper investigates the quantum nature of a strongly coupled single quantum dot (QD) and cavity system, focusing on the interaction between a QD and a photonic crystal (PC) nanocavity. The authors demonstrate that the QD-cavity system exhibits quantum correlations in photoluminescence (PL) when the QD is precisely positioned at the cavity's electric field maximum. When off-resonance, photon emission from the cavity mode and QD excitons are anti-correlated at the single-photon level, confirming that the cavity mode is driven solely by the QD. When tuned into resonance, the system enters the strong-coupling regime of cavity-QED, reducing the QD lifetime by a factor of 120 and causing the photon stream from the cavity to become anti-bunched, indicating the system is in the quantum anharmonic regime. The study confirms the feasibility of achieving quantum information processing tasks in the solid state, particularly in the quantum nonlinear regime. The experimental techniques used include precise positioning of the nanocavity to a single QD, spectral tuning of the cavity mode, and measurement of quantum correlations in PL. The results provide strong evidence for the quantum nature of the QD-cavity system and support the pursuit of solid-state cavity-QED for quantum information processing.