The World’s Tiniest Clock Is Just One Atom

Holger Muller, a physicist at the University of California at Berkeley, and his colleagues were interested in breaking down time-telling to its simplest possible forms, and a single-atom clock seemed like a good place to start. The whole concept relies on Broglie's matter-wave hypothesis, which states that a particle of matter can behave like a wave. That means it'll oscillate in a normal pattern that can be used as a clock.

It's not quite that simple though; a single atom will oscillate too fast to be read. So the researchers basically split a cesium atom in half, and had one half move back and forth. Because this movement dilated the oscillation of that half, and the scientists knew exactly how they'd disrupted the atom, they were able to use all the data to calculate the oscillation of the original atom, and essentially make a single atom clock out of it.

A one-atom clock is awesome, but not exactly great at its job. It's only about as accurate as the first atomic clocks, and one billion times less so than the nuclear clocks we have today. Still, it's an impressive accomplishment. More here.