Transient internal dynamics of a multilevel ion

Abstract

The autocorrelation ${\mathit{g}}^{(2)}$(\ensuremath{\tau}) of the photon-counting signal from laser-induced light scattering off a single trapped and laser-cooled ${\mathrm{Ba}}^{+}$ ion shows dramatic nonclassical effects: ${\mathit{g}}^{(2)}$(\ensuremath{\tau}) increasing upon delay \ensuremath{\tau} close to zero (``antibunching'') is accompanied (i) by its extreme peak values, (ii) by long transients and long appearance of subunity values (``sub-Poissonian light''), both extending much beyond the lifetime of the ion's resonance level, and (iii) by modulation from magnetic precession, as is common with quantum beats. These phenomena highlight the internal multilevel structure of the ion, hint at optical pumping, and prove the coherent evolution of the ion's internal state. The preparation of the ion in a coherent superposition by spontaneous decay is demonstrated. The counting variance of the scattered light, measured in terms of Mandel's Q parameter, deviates from that of classical light by up to \ensuremath{\Delta}Q=-7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$.