In standards labs around the world, physicists are building and testing the next generation of atomic clocks. Like their cesium-based forebears, the new clocks keep time by locking onto atomic resonances. To deliver high accuracy, a resonance must be sharp, but it must also be stable.
Because high frequency brings high stability, clockmakers seek optical transitions. And because the environment undermines stability, they work with single atoms or ions isolated in traps.
Spectrally speaking, the singly charged aluminum cation looks ideal for making an atomic clock. One of its hyperfine transitions (1 S 0→3 P 0), has a Q of 2 × 1017 and barely wavers under the influence of stray electric and magnetic fields that leak from lab equipment.
But aluminum has an unfortunate drawback. Unlike the current favorite ions of atomic clockmakers—strontium, ytterbium, and mercury—aluminum lacks a convenient transition for removing kinetic energy....
