Abstract

The potential for high-accuracy spectroscopy and improved frequency standards has motivated research with trapped ions in recent years. Two possible limitations on performance are the uncertainty in the second-order Doppler shift and the signal-to-noise ratio. With a single ion in a rf quadrupole trap, the uncertainty in the second-order Doppler shift can be smaller than 1 part in 10¹⁸. For a good signal-to-noise ratio we would like to have a large number of ions. However, in the rf quadrupole trap, as the number of ions increases, so does the second- order Doppler shift because ion-ion repulsion displaces the ions from the center of the trap.

© 1991 Optical Society of America