Abstract

Laser-cooled ions in radiofrequency traps offer unique possibilities for experiments on isolated quantum systems and for frequency metrology since long interaction times with external radiation fields are possible in an environment with small perturbations. The ytterbium isotope ¹⁷¹Yb⁺ has a nuclear spin I=1/2 so that reference transitions without linear Zeeman frequency shift are available in a level system with relatively simple sublevel structure. The cycling F= 1-F=0 component of the alkali-like ²S_1/2−²p_1/2 resonance transition of ¹⁷¹Yb⁺ permits efficient optical detection and laser cooling if population of the ²D_3/2(F=1) sublevel is avoided by additional excitation to a higher-lying level (see Fig. 1). The λ=435.5nm ²S_1/2 - ²D_3/2 electric-quadrupole transition of ¹⁷¹Yb⁺ has a natural linewidth of 3 Hz. Transitions to the ²D_3/2(F=2) sublevel are easily detected by electron shelving, i.e., by the observation of dark times in the emitted resonance fluorescence¹. We here report experiments where the ²S_1/2(F=0) - ²D_3/2(F=2,m_F=0) transition of a single trapped ¹⁷¹Yb ion is resolved with an optical linewidth of less than 100 Hz.

© 1998 IEEE