Emission rate of a multilevel atom and its quantum beats

Using the Heisenberg operator approach, we have calculated the emission rate of a multilevel atom whose transitions involve both upper- and lower-state splittings. The emission rate is first calculated by a frequently used power-flow expression and is shown to exhibit lower-state beats. This power-flow expression requires care in its interpretation because it does not account for the measurement process. We then derive an alternative, detection-oriented emission rate and show that lower-state beats are not observable in a photodetection experiment.