内容摘要：Resonance fluorescence from a coherently driven two-level emitter is conventionally described using mixed-state field correlations. In this talk, I will present a complementary perspective that emerges through few-photon excitation, in which the emitter and its spontaneous emission are described within a unified quantum-state framework. This picture provides an intuitive understanding of how phase coherence and photon antibunching coexist in resonance fluorescence. I will show how the model accounts for a range of recent observations and leads to experimentally testable predictions, including interference between mutually detuned resonance-fluorescence fields, tunable higher-order coherence through interference with laser light, and the synthesis of nonclassical and entangled photonic states using only passive linear interferometry. More generally, this framework offers a useful way to understand resonance fluorescence and its coherence properties, complementary to the conventional field-correlation approach.