The photon pair correlation in the laser-excited fluorescence of a single trapped and cooled ${\mathrm{Ba}}^{+}$ ion shows antibunching and, in addition, novel nonclassical phenomena absent in the fluorescence of two-level atoms. They include excessive transient values of the correlation caused by optical pumping, and temporally extended sub-Poissonian photon emission probability which arises from the transient excitation of nonabsorbing Raman coherence. The fluorescence also displays sub-Poissonian photon statistics.

• Received 3 September 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.3016