  We study the dynamics of an atomic two-level system decaying by spontaneous
emission of light. Subject to continuous detection of the radiated field, the
system tends with certainty to the ground state in the long time limit, but at
initial times the excited state population exhibits non-trivial stochastic
behavior. Employing methods from Ito calculus, we characterize this behavior,
and we show, for example, that the emitter, as a result of in-phase homodyne
measurements, may become fully excited during the decay process while
heterodyne and out of phase homodyne measurements do not drive the atom
completely into the excited state.
