We take GPS so much for granted on land that it's easy to forget where GPS doesn't work—like deep underwater, where only strange sea creatures and submarines roam. Enter the bizarre new world of quantum positioning, where supercooled atoms could be the future of navigation.


The UK's Defence Science and Technology Laboratory (DSTL) is leading the way in quantum positioning, as reporter Paul Mark discusses in a recent article for New Scientist. Submarine navigation today still relies on accelerometers, which records a sub's movements from a last known position. The longer the sub roams without surfacing for a GPS "fix" on its position, the less accurate the path plotted by its accelerometers.

A day without a GPS fix can take a sub a kilometer off course. By contrast, quantum accelerometers could be a thousand times more accurate with an error of just one meter. New Scientist explains how such an accelerometer could work.

To create the supersensitive quantum accelerometers, [the DSTL] team was inspired by the Nobel-prizewinning discovery that lasers can trap and cool a cloud of atoms placed in a vacuum to a fraction of a degree above absolute zero. Once chilled, the atoms achieve a quantum state that is easily perturbed by an outside force – and another laser beam can then be used to track them. This looks out for any changes caused by a perturbation, which are then used to calculate the size of the outside force. The DSTL team wants this set-up to be usable in the real-world setting of a submarine, where the size of the force would correspond to the movements as the sub swings around in the sea.


Right now, DSTL only has a prototype, a "1-metre-long shoebox" that records one axis of motion to be tested next year. It'll need more lasers and more supercooled atoms of rubidium to navigate in all three dimensions.

But the ultimate challenge with quantum positioning may be its exquisite sensitivity. Even tiny amounts of gravity could confuse the accelerometer "If the submarine passes an underwater mountain whose gravity attracts it to the west, that feels exactly like an acceleration to the east," says Edward Hinds at the Centre for Cold Matter at Imperial College London told New Scientist."

Still, if we do figure out quantum positioning, it need not be confined to the water—it could be an extra layer of backup in cars, planes, and even cellphones when GPS signals are blocked. It wasn't so long ago that receiving signals from space might have seemed like an outlandish way to navigate—why not supercooled atoms? [New Scientist]

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