Ultrafast laser pulses can be used to detect the motion of a single atom, from energetic wiggles to quantum jitters.

Kale Johnson at the University of Maryland in College Park and his colleagues trapped ions of ytterbium and zapped them with laser pulses just 10 picoseconds long. The pulses gave the atom small kicks in momentum of different magnitudes, depending on its internal state. This resulted in a new state that encoded the atom's original motion. After another sequence of pulses, the researchers observed fluorescent light from the atom that allowed them to measure its quantum motion.

The technique could be useful for future quantum computers built from trapped ions, the team says.

Phys. Rev. Lett. 115, 213001 (2015)