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An atom laser that produces a beam of matter with a precise fixed frequency could eventually lead to a new generation of ultra-sensitive navigation devices.

The laser overcomes some of the problems that have plagued atoms lasers since they were first built in the late 1990s.

Atom lasers do with matter what conventional lasers have done with photons since the 1950s - produce a bright beam of coherent waves. This is possible because the wave-particle duality of matter means that atoms have an associated wavelength that can be manipulated in a similar way to light waves. In theory, it should be possible to produce a beam of atoms with a single precise frequency, in which all the atoms march in step.

In 1997, Wolfgang Ketterle and colleagues at MIT in the US, created the first atom laser by cooling a group of atoms to such an extent that their wave-like states overlap - a so-called "Bose Einstein Condensate". The team then used a magnetic field to extract atoms, creating a beam of atoms with the same wavelength.

The problem is that, once these atoms are extracted, gravity makes them accelerate, changing their wavelength. "One of the problems is that you don't have a well-defined wavelength and that is annoying," says Alain Aspect, the physicist who led the development of the new laser at the Charles Fabry Laboratory at the Institute of Optics in Paris, France.

Perfectly aligned

Aspect's group got around the problem of using another light-based laser to ensure that the beam is perfectly horizontal, counteracting the effect of gravity - a feat that requires extraordinary precision. "Everything has to be perfectly aligned," he says. "You have to realise that this laser is very difficult to build."

The result is a beam in which the wavelength does not change. "That is a useful point," says Charles Adams, an atom laser expert at the Durham University. "If you want to carry out experiments such as atom interferometry, you don't want the wavelength changing."

The payoff could be significant. Atom lasers are still poorly understood because, unlike photons, atoms interact