Top clock now a distant second

By Bill Scanlon, Rocky Mountain News (Contact)

Published March 10, 2008 at 12:30 a.m.

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When it comes to accurate atomic time pieces, aluminum is the new flavor of the month.

Just a month after Boulder scientists announced they had developed a state-of-the-art strontium atomic clock, another group of Boulder scientists has eclipsed even that accuracy.

How accurate? How about losing one second every billion years?

With accuracy like that, scientists can measure whether the fundamental constants that describe the universe are changing ever so slightly.

If they are, our basic assumptions about the universe may have to change.

Till Rosenband, a scientist with the National Institute of Standards and Technology, led the effort to develop the aluminum clock.

It applies the logic of computers to the peculiarities of the quantum world.

It relies on the natural vibrations of ions, which are electrically charged atoms.

A paper on the new clock appears in the latest issue of Science Express.

There is another experimental clock, using a single mercury ion, that has the potential of being slightly more accurate than the aluminum clock, but Rosenband notes that aluminum has advantages over mercury.

For one, it keeps working if temperatures fluctuate as well as in the presence of background magnetic and electric fields, he said.

"It has the lowest known sensitivity of any atomic clock to temperature, which is one of the most difficult uncertainties to calibrate."

The current time standard clock, also developed by NIST, uses ions vibrating at microwave frequencies.

The newest generation clocks, all competing to become the new standard in the coming years, operate on optic frequencies - 100,000 times higher than microwave frequencies.

Optical clocks divide time into much smaller units, so can be far more precise.

The precise clocks won't make a difference in getting to work on time, but they're essential in synchronizing telecommunications networks. And they play a key role in satellite navigation and positioning for commercial and military purposes.

Also, the trillion-plus vibrations per second can lead to the development of new gravity sensors to help explore for riches below the earth.

The aluminium clock is a spinoff of NIST's work on quantum computers, which itself was a spinoff of NIST's earlier work on atomic clocks.

By nudging atoms into a state in which they are, paradoxically, in two places at the same time, and then back again to a single state, scientists can achieve the Holy Grail - letting a single atom stand for both the zero and the one in a binary system.

If so, a relative handful of atoms can do faster and more complicated calculations than all the computers in the world working together.

The new NIST quantum logic clock uses aluminum and berylium, confined close together in an electromagnetic trap. Lasers pointed at the atoms slow them to near absolute zero temperatures, the temperature at which nothing moves.

Aluminum is stable when it comes to ticking off the tiny units of time, but aluminum is hard to detect with lasers. That's why the scientists paired it with berylium. They detect the aluminum clock ticks by observing light signals from the berylium atom.

Scientists use other atomic clocks to calculate the accuracy of the newest models.

In so doing, the NIST scientists are able to search for a change over time in something called the "fine structure constant," which measures the strength of electromagnetic interactions.

Astronomers have made discoveries suggesting that the "fine structure constant" is changing very slowly over billions of years.

Uh-oh. If that's true, they'll have to rework their theories on the nature of the universe.

The tests have shown that the constant may be not moving at all or may be moving as fast as 1.6 quadrilionths of 1 percent per year.

Sounds like a job for an even more accurate atomic clock.

scanlon@RockyMountainNews.com or 303-954-2897

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