Monitoring a single ion's motion by second-order photon correlations

Abstract

For a single trapped ion, second-order time correlations of fluorescence photons are measured in a self-homodyne configuration by beating the fluorescence with itself. At the nanosecond timescale, the correlations are governed by electronic excitation and decay of the ion and anti-bunching in the resonance fluorescence is observed and quantitatively reproduced. On the other hand, at the microsecond timescale the motion of the ion determines the correlations: secular motional modes, their amplitude and relative coherence are measured. Besides precisely monitoring the trap frequencies, our observations also quantify the temporal stability of the trapping potential.