An entangled photon source for resonant single-photon-single-atom interaction

We present the development and operation of a tunable, frequency-stabilized, narrow-bandwidth source of entangled photon pairs, which can be tuned to the two D-P transitions in Ca(+) ions at 850 and 854 nm. The source is based on spontaneous parametric down-conversion in periodically poled KTiOPO(4) (PPKTP) followed by tunable optical filters. Its output bandwidth of 22 MHz coincides with the absorption bandwidth of the calcium ions. Its spectral power density is 1.0 generated pairs (s MHz mW)(-1). Here, we report details of the setup which was first described in Haase et al (2009 Opt. Lett. 34 55).