The US Has a New, Super-Accurate Atomic Clock

Three times as accurate as its predecessor, it'll only lose a second over 300 million years.

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Apr 4 2014, 10:50am
Image: Youtube/NIST

Up until now, the clock by which US time was set—the standard used by the National Institute of Standards and Technology (NIST)—was an atomic clock so precise it would only stray a single second over a period of 100 million years.

With such precision, you might have thought there’s little room (or time) for improvement. But in their ongoing quest to reach ever more standardised standards, NIST has launched a new atomic clock that’s three times as accurate. That is, it won’t gain or lose a second in 300 million years.

NIST-F2 is the most accurate clock of its kind in the world, and it’ll join its predecessor NIST-F1 in setting the standard for US civilian time and frequency (military time is maintained by the Naval Observatory instead), keeping the country punctual to within fractions of fractions of fractions of seconds.

You might be wondering around about this exact second why anyone would need a clock that’s quite so accurate. By the sound of things, NIST isn’t quite sure yet either.

All it knows is that whenever time-keeping has improved previously, it’s been used in advanced technologies like GPS, telecommunications, the internet, and so on. Banks and computer systems synchronise with NIST to keep time stamps in check. “If we've learned anything in the last 60 years of building atomic clocks, we've learned that every time we build a better clock, somebody comes up with a use for it that you couldn't have foreseen," Steven Jefferts, NIST physicist and lead designer of NIST-F2, said in a statement.

Video: Youtube/NIST

He elaborates on this in the above video. “When you can do something better than the Earth gives you naturally in its rotation, well you go ahead and you start down that road,” he says. “And then people keep making it better, and when you make it better somebody starts having a use for it, and so you have to make a better one.” 

He later adds, “The short answer is there’s probably no relevance for the best clock we can build today in everybody’s life tomorrow, but that clock is going to be the progenitor for something that really is important ten years from now, I would predict.”

Like NIST-F1, NIST-F2 is made of a cesium fountain—which essentially means cesium atoms are thrown in the air and fall back down into a tube repeatedly. There are also other ways of measuring super-accurate time, but for those interested in trying to get their head round the physics of cesium fountain clocks, NIST has a handy backgrounder

During the trip, some atomic states of the atoms are altered, while others remain the same, as they interact with a microwave signal from a maser. When the trip is finished, another laser is pointed at the atoms. Some atoms—those whose energy states were altered by the microwave signal—emit light, or fluorescence. The resulting photons, the tiny packets of light emitted, are measured by a detector.

This process is repeated while the microwave signal in the cavity is tuned to different frequencies. Eventually, a microwave frequency is found that alters the states of most of the cesium atoms. This frequency is the natural resonance frequency of the cesium atom (9,192,631,770 Hz), or the frequency used to define the second.

Got that? As Jefferts puts it, “If I count 9,192,631,770 cycles of the radiation that makes the electron flip over, then that’s one second … So you simply keep counting.”

Voilà a definitive second. But NIST-F1 was already doing all that, so how is NIST-2 better? The main improvement is a liquid nitrogen cooling system that keeps the atoms at -193 degrees C (-316 F), and reduces background thermal radiation that can cause (very) small errors in the atoms’ ticking.

NIST-F1 and NIST-F2 will be working alongside each other for now to set the standard for US civilian time. And while there might not be any specific application of the new clock just yet—aside from a newly awesome level of super-human time-keeping—there is one reason ever-better clocks are needed. Quite simply, as the tech trickles down to the market and everyone gets more accurate clocks, something has to set the standard.

“The clocks they sell are as good as the clocks we could possibly build in the laboratory 20 years ago, and they’re being used all over the place,” said Jefferts. “And so we have to stay out in front of that, if for no other reason than we have to be able to calibrate them.”