News in Science

New atomic clock to time the cosmos

Time machine Australian scientists are racing against time to build one of the most precise atomic clocks ever made, for an experiment to measure one of the fundamental constants of the universe.

The clock, which uses atoms of the rare earth element ytterbium, is being built by researchers led by Associate Professor John McFerran at the University of Western Australia.

"Rather than clocks, I like to think of them as humankind's ultimate accuracy machines," says McFerran.

Unlike standard atomic clocks using microwaves, ytterbium clocks will operate at much higher optical frequencies enabling time to be divided into shorter intervals about a hundred thousand times smaller, for more precise measurement.

"To build it, we need a collection of lasers, optics, electronics, stainless steel and an ultra high vacuum system to isolate the atoms," says McFerran. "Each laser system is almost a PhD or masters thesis in itself."

The laser system cools and slows down the ytterbium atoms, and in combination with a magnetic field, traps them in a lattice, where they're hit with an ultra-pure highly stable yellow laser at a very specific frequency.

This causes electrons in the atom to transition to a higher energy state.

"This yellow laser represents the closest thing to a pure sine wave," says McFerran.

"Think of the purest musical note you have ever heard and then multiply the clarity by over a billion times, that's how pure the sine wave needs to be."

Space bound

When completed, it will be the nation's only cold atom optical clock, and the only southern hemisphere based clock in the international Atomic Clock Ensemble in Space (ACES) project.

ACES is scheduled to launch to the International Space Station in 2016, to help determine if one of the unchanging laws of physics, the fine structure constant, is the same everywhere.

The fine structure constant, is the strength of the electromagnetic force binding electrons to the nuclei of atoms.

Over three years, the frequency ratios of the clocks will be compared to evaluate whether the fine structure constant is changing.

"Astronomical observations suggest that this has changed over the eons, the billions of years of the universe," says McFerran.

"It may be different in different directions, and so the atomic clock community is on the hunt to see if we can detect such changes."

Just a second

As well as pure research, such as testing the laws of physics, atomic clocks are used to define time itself.

"At the moment our second, the unit of time, is based on the transition in caesium which is 9,192,631,770 cycles per second," says McFerran.

"Had we had the level of accuracy back in the 1970s that we have now, we would have had the last three digits in that definition as 997 rather than 770, and then we wouldn't have had to put in place a leap second every few years."

As well as ytterbium, aluminum, mercury and strontium atomic clocks are also being developed around the world, to determine which combination of clocks is most suitable for a future international standard definition of the second.