Precise test of quantum jump theory

Quantum jumps due solely to spontaneous Raman scattering between the Zeeman sublevels of a single ²⁴Mg⁺ ion have been observed in the fluorescence emitted by the ion. A theory of quantum jumps for this system predicts that coherences between excited levels cause the ratio of the mean duration of the ``fluorescence-on periods'' to the mean duration of the ``fluorescence-off periods'' to be independent of laser intensity. The measured value agrees with the predicted one to within the measurement precision of 2%. The distribution of the durations of the off periods also agrees with theory.