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Ultra-precise clocks

Another practical applications of atoms at very cold temperatures has already been realised; the development of ultra precise clocks that lose less than one second in 100 million years.

Atomic clocks operate using the natural frequency of the atom. Every atom of a particular type – say rubidium – has electrons at certain energy levels. A photon hitting a rubidium atom will bounce one of its electrons into a higher energy level, creating a measurable frequency – this is the tick of the atomic clock.

At very cold temperatures, though, it is much easier to measure the natural frequency of the atoms (the clock's 'tick'), meaning cold atoms make more accurate clocks. Cold atom clocks are created by laser cooling, in tandem with the use of microwaves to form a gravitational trap – a so-called 'atomic fountain'.

Atomic clocks can accurately measure extremely subtle variations in physical parameters, such as changes in the Earth's gravitational field.

"In a few years clocks will be able to monitor local changes of the Earth gravitational potential by using relativity, which might help us forecast tsunamis, earthquakes, or global climate warming," said quantum physicist Christophe Salomon, director of the cold Fermi gas group at the Superior Normal School, in Paris, France and principal investigator for the ACES (Atomic Clock Ensemble in Space) space clock mission.

Cold beams of matter

Also in development by cold atom scientists are atomic lasers. Atomic lasers are created from a super cold cloud of atoms. Slowly releasing the atoms in a steady stream creates lasers made from focused beams of matter rather than light.

Atomic lasers could be used to make extremely accurate sensors for magnetic, electric and gravitational fields or to make precise measurements of rotation and accelerations, for instance on satellites or spacecraft that are out of reach of radio signals.

Recently, scientists from the Australian National University in Canberra published the details of the world's first refillable atom laser in journal Nature Physics. Built by the same team that produced the first BEC in Australia, in 2001, the ANU team created an atom laser using a cloud of BEC that taps into a neighbouring cloud to refuel; much like a water bucket is refilled by a tap.

Although currently expensive and confined to research labs, devices based on atom lasers will find uses in the real world, says John Close, head of the ANU's Atom Laser Group. These uses might missiles that secretly track their own path, or spacecraft that can navigate without assistance from Earth. But we'll probably have to wait at least another two years before the first practical devices that contain atoms lasers are built, he adds.

In the meantime, as scientists push closer to the ultimate cold, their path is a road strewn with discovery.

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