Efficient coherent internal state transfer in trapped ions using Stimulated Raman Adiabatic Passage

We demonstrate experimentally how the process of Stimulated Raman Adiabatic Passage (STIRAP) can be utilized for efficient coherent internal state transfer in single trapped and laser-cooled $^{40}$Ca$^+$ ions. The transfer from the D$_{3/2}$ to the D$_{5/2}$ state, is detected by a fluorescence measurement revealing the population not transfered to the D$_{5/2}$ state. A coherent population transfer efficiency at the level of 95 % in a setup allowing for the internal state detection of individual ions in a string has been obtained.