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Nist: New Optical Clock More Accurate Than Cesium
LordPhatal writes "NIST researchers have demonstrated a new kind of atomic clock that has the potential to be up to 1,000 times more accurate than today's best clock. The new clock is based on an energy transition in a single trapped mercury ion.
The NIST labs out in Boulder, CO is a fabulous place to go and visit if you ever find yourself in town, or in Denver. They will gladly take you on a tour, and show you all sorts of interesting toys that they have. Probably the best part of the tour for me was the liquid hydrogen. Even better was touching it. Yes I did, yes I still have all my digits. Basically, it is exactly the same concept as fire; move your hand thru it very quickly. In this case, touch it quickly and retract. The tour guide also shrank a balloon completely down, as we all watched, as it slowly got bigger when he took it back out. And of course on the tour, was getting to see the atomic clock. (On the other side of a window of course.) Check it out!
And if you are in Boulder, and enjoy tea, make sure to take a tour of the Celestial Seasonings Tea Plant. If you have sinus problems, their Peppermint room will take care it, pronto.
With a cesium-133 atom, a second is the time needed for the atom to perform 9,192,631,770 complete oscillations.
--Metrollica
Basically, the accuracy of a reference clock in principle determined by making two identical clocks, starting them synchronized, and measuring how long before they drift by an average of 1 second.
This has to do with how cold your atomic fountain is, and how well you isolate the particular magnetic sublevel you define the second in terms of.
Now, if you want to move to a mercury standard clock, you can do two things: first, calculate with QED the ratio of the freqencies between the transitions in cesium and mecury of interest. I don't know if we can do this well enough for these purposes or not. Second, you can redefine the second in terms of the oscillation frequency of some mercury transition at least within the accuracy of a current cesium clock.
The important thing to note is that mand physicists don't really care about how long a second is, as much as they care that two clocks run at the same rate, even if it is wrong.
The above wording is imprecise. 9,192,631,770 Hz is the frequency of the electromagnetic wave that triggers a certain transition in a cesium-133 atom. So, what oscillates is not the complete atom, but the electric and magnetic field. Details can be found here
Funny thing, today I was just reading the Java API documentation for the java.util.Date class, which has many good time related links, on in particular explaining why astronimical time measurements are not accurate enough, at least over shorter time periods.
One advantage of the new clock is that it ticks much faster. Today?s international time and frequency standards, such as NIST-F1, measure an atomic resonance of about 9 billion cycles per second. By contrast, the new NIST device monitors an optical frequency more than 100,000 times higher or about 1 quadrillion (US) cycles per second.
A 9 GHz oscillation can be hooked up directly to electronic circuits, counters, PLLs, etc. My first question when I read this article was, how the heck do you synchronize anything else to a "frequency" that's in the optical / ultraviolet range? I found some more information on this page and this one, so I guess that's how this new clock works.
Actually, the meter is now defined as the distance light travels in vacuum during 1/299 792 458 of a second. This happened in 1983. Originally, it was 1 / 10 000 000 the distance between a pole and the equator, but that was way back in 1793.
Check this link for more details.
Originally, the second was defined to be 1/86,400 of the mean solar day. Because this is inaccurate due to irregularities in the Earth's rotation, that is the length of the second would change, finer standards were chosen. These finer standards are based on the original standard, but because they are defined in another way, they will not change unless the fundamental properties of the universe do.
"The price of freedom is eternal vigilance." - Thomas Jefferson