Observation and temperature measurement of the sympathetically cooled ions in an rf trap

The barium ions are trapped with the laser-cooled magnesium ions simultaneously in an rf trap and cooled sympathetically. Sympathetically cooled ions are one of the candidates of accurate optical frequency standard. The barium ions are ionized by the charge transfer with the magnesium ions for avoiding the loss due to the shallow trapping potential. The temperature of the barium ions is measured and the effect of the sympathetic cooling is observed. It is also found that the application of the ionization by the charge transfer to other ion species is possible.