Quantum compass promises sat-nav alternative

Britain

There is a problem shared by nuclear submarines, infrastructure-critical oil tankers and anyone trying to find gate 72 at Heathrow terminal 4.

GPS is unreliable. It can be fooled by everything ranging from being indoors to being interfered with by foreign powers.

Now a British company has a device that could help: a quantum accelerometer that can tell precisely where you are, using supercooled rubidium atoms that even the Russians cannot meddle with. The prototype ‘‘quantum compass’’, revealed at a conference in London, is able to detect the slightest change in speed so that, in theory, as long as you know your initial position it can work out from the perturbation of atoms where you have gone afterwards.

As the world has become more reliant on navigation satellites, military and civilian authorities have grown concerned about how vulnerable they are.

It is not only that they don’t work well without a clear line of sight. The signal is also easily blocked.

The answer, believes Joseph Thom, of the Glasgow-based company M Squared Lasers, is a box full of atoms.

His system is based on a technology older than GPS, called inertial navigation. Devices use sensors to tell when they are being accelerated and in what direction, meaning that if the system knows its start position it can in theory calculate everything coming after. The problem is that such systems ordinarily drift and need regular calibration which in the case of a submarine, for instance, means returning to the surface.

With atoms, you can eliminate almost all that drift. The system uses rubidium atoms cooled to almost absolute zero, which are allowed to fall freely. Any slight acceleration is picked up by looking at the quantum mechanical interference patterns produced as they drop. – The Times