Sunday, August 25, 2013

Housing the World's Most Precise Clock

Keeping Time

Precision Timepiece: NIST Boulder’s Ytterbium atomic clock is the most-precise clock in
the world, an article in PopSci says. “The NIST clocks are optical lattice clocks, which means 

they have an intense laser field that holds about 10,000 ytterbium atoms in place. Another laser
excites the atoms, the movement of which is how the clock measures time. Exciting the atoms with
a laser makes them vibrate at higher frequencies than atoms in cesium atomic clocks do. So optical 

lattice clocks tick faster and are able to tick off more precise units of time. Having so many atoms 
in the clock helps average out the uncertainties from any one atom.”
Photo CreditBurrus; NIST
Source: PopSci

An article, by Francie Diep, in Popular Science says that the National Institute of Standards and Technology in Boulder, Co., has made the world’s most precise clock using atoms of ytterbium, a rare Earth element. These clocks are part of a latter-day technology called optical-lattice clocks, which are about 100 times more stable than the previous standard, cesium atomic clocks.

Diep writes
It’s so precise that, because it outstrips other atomic clocks, its creators weren't able to measure its precision until recently, when they built a second version of it. Now, with the two available to compare with one another, they've come up with a number for the clocks’ precision, which clock physicists call the clocks’ stability.
“Clock stability is a term we use in the field that basically refers to—if you look at the ticking rate of the clock, how much does that ticking rate change over time?” Andrew Ludlow, a NIST Boulder physicist who works on improving the lab's atomic clocks, tells Popular Science. “Ideally, you want every tick to be exactly the same as the other.”
The NIST Boulder clocks have an instability of one part in 10-18. That's about 100 times more stable than the best cesium atomic clocks that international governments use to define the perfect second. And it’s about 10 billion times more stable than quartz wristwatches.

The NIST Boulder clocks are made with technology a generation beyond that used in cesium atomic clocks. They happen to use atoms of ytterbium, a rare Earth element, but other next-generation clocks around the world use other elements, such as strontium and mercury. These next-generation clocks could be used to measure some pretty cool effects in fundamental physics.
For example, Einstein's theory of relativity has been devilishly difficult to prove experimentally. A NASA satellite measured the warping of space and time around Earth just in 2011. Next-generation atomic clocks, however, could measure the effects of relativity right here on Earth.
The theory of relativity says that in the presence of a strong gravitational field, time should slow; this makes a highly precise clock all the more necessary to test and validate this theory. The current NIST clock is too large and too fragile to be used for this purpose, and thus NIST, with the funds it has has received from the U.S. government, has plans to build such a portable clock.

You can read the rest of the article at [PopSci]