Observation of an Electric Octupole Transition in a Single Ion

The ${}_{}{}^2{}_{}{}^{}S_{1/2}^{}{}_{}{}^{}-{}_{}{}^2{}_{}{}^{}F_{7/2}^{}{}_{}{}^{}$ electric octupole $\left(E3\mathrm{}\right)$ transition in ${}^{172}{\mathrm{Yb}}^{+}$ has been detected by observing quantum jumps in a single laser cooled ion, stored in an electrodynamic trap. The transition frequency is 642 116 785.3(0.7) MHz $\left(1\sigma \right)$. Consideration of the transition rate and laser parameters implies a ${}_{}{}^2{}_{}{}^{}F_{7/2}^{}{}_{}{}^{}$ level lifetime of 3700 days. This is the first time an atomic $E3\mathrm{}$ transition has been driven. This transition has applications as an optical frequency reference.