Resonant interaction of a single atom with single photons from a down-conversion source

We observe the interaction of a single trapped calcium ion with single photons produced by a narrow-band, resonant down-conversion source [ A. Haase et al., Opt. Lett. 34, 55 ( 2009)], employing a quantum jump scheme. Using the temperature dependence of the down-conversion spectrum and the tunability of the narrow source, absorption of the down-conversion photons is quantitatively characterized.