When an aircraft is on final approach or a submarine is navigating blind, the navigator needs an instrument that never loses track of motion. Conventional gyroscopes based on atomic waves are extremely precise, but they have a quirk: the signal repeats like a wallpaper pattern, and after half a step, the pattern starts to look the same. The instrument loses its sense of position.
In the new work, this quirk has been circumvented. They took a continuous beam of rubidium atoms, cooled it perpendicular to its motion, and passed it through two laser gratings. The atoms, like swimmers, dive into the light waves, and by how they emerge, you can tell where and how fast the entire setup is moving. Previously, they tracked a single wave crest; now they track the entire series of crests, and the laser automatically adjusts its frequency to stay on track.
The instrument was tested continuously for a thousand seconds: over that time, it accumulated an error of only four micro-g in acceleration and four ten-thousandths of a degree per hour in rotation. For comparison: in an hour, the needle of such a compass would deviate less than the thickness of a hair, viewed from arm's length.
Now atomic sensors can do more than just produce pretty interference patterns; they can work as true navigational instruments. This is a step toward aircraft, ships, and satellites orienting themselves by quantum laws without relying on GPS.
Rubidium is a soft metal that melts at just 39 degrees Celsius. In the sensor, its atoms are laser-cooled to near absolute zero so they move slowly and uniformly, like soldiers in a parade.