Ion-number-density-dependent effects on hyperfine transition of trapped 199Hg+ ions in quadrupole linear ion traps

The ion-number-density-dependent frequency offsets and broadening of the ground state hyperfine transition spectra of trapped H199g+ ions were measured as a function of the end-cap voltage of the quadrupole linear ion trap. The number density of trapped H199g+ ions in the quadrupole linear trap was controlled by the end-cap voltage. The fractional frequency stability of H199g+ hyperfine transition to the 1 mV end-cap voltage variation was preliminary estimated to be less than 1×10−16. The causes of the ion-number-density-dependent frequency shift and spectrum broadening were analyzed theoretically and explained.