Damped Population Oscillation in a Spontaneously Decaying Two-Level Atom   Coupled to a Monochromatic Field
  We investigate the time evolution of atomic population in a two-level atom driven by a monochromatic radiation field, taking spontaneous emission into account. The Rabi oscillation exhibits amplitude damping in time caused by spontaneous emission. We show that the semiclassical master equation leads in general to an overestimation of the damping rate and that a correct quantitative description of the damped Rabi oscillation can thus be obtained only with a full quantum mechanical theory. 
Sun Kyung Lee, Hai-Woong Lee