Changing the clocks, and it's about time

THOSE who keep time never tire of looking for refined ways to measure it.

THOSE who keep time never tire of looking for refined ways to measure it.

The clock of the atomic age is based on measuring the oscillations of the element caesium, but as the National Measurement Institute's Bruce Warrington puts it: "Laboratories and theoreticians all over the the world are thinking (about) how to make a better clock."

"And although you may have thought of it as a solved problem, it's changing all the time," says Warrington, whose PhD in atomic physics has led him to his position as section manager for length, time and optical standards.

The main types of caesium clocks are fountain clocks, in which atoms are tossed metres into the air and the frequency of the transition they make between two energy states is observed, and the less accurate beam clocks that shoot the atoms horizontally across a much shorter space.

Accuracy is a super-fine distinction at this micro level. Fountain clocks would take about 30 million years to gain or lose a second, while beam clocks would take about 30,000 years.

While Warrington continues to work with the beam clocks such as the one pictured, which he refers to as the size of "overgrown VCRs", award-winning University of NSW theoretical physicist Victor Flambaum has just completed research that makes it possible that some day a modified version of a caesium clock will be easily portable. Flambaum, working with UNSW colleague Vladimir Dzuba and the University of Nevada's Andrei Derevianko have studied how to measure time within an optical "lattice" of caesium, rubidium and two other atoms. Such lattices are ideal because they are tiny, less than one cubic millimetre.

But the laser field that creates the lattice also distorts the atoms' oscillation. "We have got rid of this problem by working out how to specially angle the magnetic field," Flambaum says.

His team's paper was published last month in the American Physical Society's journal Physical Review Letters.

"We want to make the clock portable, for example, for applications in space, where size and weight are limited." There remains one issue: "The thing was to make it competitive in terms of accuracy."

But, Flambaum says, even if such clocks are less precise than fountain clocks, they could still be useful in navigation systems and for precision tests in space. The research has been greeted with enthusiasm around the world.

Warrington endorses the potential new development. "Sometimes there is a gap between developing new technology and its practical applications but it is always used in the end. When people built the atomic clock the first time they didn't need that level of accuracy, but then someone worked out you could use it for global positioning systems."