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Boffins build super-accurate atomic clock

300 million years without winding

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The atomic clocks currently used for regulating international time zones are great and all, but who has the time every few million years to adjust them?

Fortunately, physicists in the US have figured out how to control seemingly "forbidden" collisions between neutral strontium atoms to make a clock that neither loses nor gains a second in more than 300 million years.

The research was done by the folks at JILA, one of the country's leading physical science research institutes, jointly run by the University of Colorado and the National Institute of Standards and Technology. Their latest findings are described in the April issue of the journal Science.

Like other atomic timepieces, JILA's strontium-based clock measures time by harnessing the natural - and conveniently consistent - vibrations of atoms.

JILA's clock - which it's been improving on for the last couple of years - traps a whole bunch of super-cooled strontium atoms in an optical grid of overlapping infrared beams. Strontium's "ticks" are measured by bathing the atoms in light from a separate red laser tuned to a frequency that prompts a uniform jump between two energy levels.

Using a whole bunch of atoms to measure the ticks increases the precision of the clock's signal, but the atoms tend to want to mingle - which messes with their internal energy states and minutely reduces overall accuracy.

Strontium belongs to a class of atoms called fermions. According to quantum physics, fermions can't occupy the same energy state and location at the same time. Therefore fermions in identical energy states can't collide. The difficulty is, in practice with JILA's clock, they do.

Scientists at JILA have now figured out that all this laser-to-atom action in the clock introduces a very small degree of inconsistency in the atoms. And once fermions are even slightly distinguishable, collisions can occur.

JILA's latest clock suppresses the atomic mayhem by reducing the strontium atoms' temperature to a few millionths of a degree closer to absolute zero and increasing the grid depth. The difference improves their previous version, which they introduced in 2008 by 50 per cent - resulting in a very impressive feat of not needing significant winding for more than 300 million years.

Ultra-precise clocks like this are actually quite useful for applications like improving the synchronization of telecom networks and deep-space communications. Also, casually mentioning that you made a clock that's accurate to a second for 300 million years is almost guaranteed to get you laid. ®

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