Phimega Group Post #53

Quantum Logic Clock is now world most precise clock
posted by soliton at Wed, 3 Mar 2010 - 09:48:39

Physicists at the US National Institute of Standards and Technology
(NIST) have built an enhanced version of an experimental atomic clock
based on a single aluminum atom that is now the world=92s most precise
clock, more than twice as precise as the previous pacesetter based on
a mercury atom.

The new aluminum clock would neither gain nor lose one second in about
3.7 billion years, according to measurements to be reported in
Physical Review Letters.*

The new clock is the second version of NIST=92s =93quantum logic clock,=94
so called because it borrows the logical processing used for atoms
storing data in experimental quantum computing, another major focus of
the same NIST research group. (.) The second version of the logic
clock offers more than twice the precision of the original.

In addition to demonstrating that aluminum is now a better timekeeper
than mercury, the latest results confirm that optical clocks are
widening their lead=97in some respects=97over the NIST-F1 cesium fountain
clock, the U.S. civilian time standard, which currently keeps time to
within 1 second in about 100 million years.

Because the international definition of the second (in the
International System of Units, or SI) is based on the cesium atom,
cesium remains the =93ruler=94 for official timekeeping, and no clock can
be more accurate than cesium-based standards such as NIST-F1.

The logic clock is based on a single aluminum ion (electrically
charged atom) trapped by electric fields and vibrating at ultraviolet
light frequencies, which are 100,000 times higher than microwave
frequencies used in NIST-F1 and other similar time standards around
the world. Optical clocks thus divide time into smaller units, and
could someday lead to time standards more than 100 times as accurate
as today=92s microwave standards. Higher frequency is one of a variety
of factors that enables improved precision and accuracy.

Aluminum is one contender for a future time standard to be selected by
the international community. NIST scientists are working on five
different types of experimental optical clocks, each based on
different atoms and offering its own advantages. NIST=92s construction
of a second, independent version of the logic clock proves it can be
replicated, making it one of the first optical clocks to achieve that
distinction. Any future time standard will need to be reproduced in
many laboratories.

NIST scientists evaluated the new logic clock by probing the aluminum
ion with a laser to measure the exact "resonant" frequency at which
the ion jumps to a higher-energy state, carefully accounting for all
possible deviations such as those caused by ion motions. No
measurement is perfect, so the clock=92s precision is determined based
on how closely repeated measurements can approach the atom=92s exact
resonant frequency. The smaller the deviations from the true value of
the resonant frequency, the higher the precision of the clock.

Physicists also evaluate the performance of new optical clocks by
comparing them to older optical clocks. In this case, NIST scientists
compared their two logic clocks by using the resonant laser frequency
from one clock to probe the ion in the other clock. Fifty-six separate
comparisons were made, each lasting between 15 minutes and 3 hours.

The two logic clocks exhibit virtually identical =93tick=94
rates=97differences don=92t show up until measurements are extended to 17
decimal places. The agreement between the two aluminum clocks is more
than 10 times closer than any previous two-clock comparison, with the
lowest measurement uncertainty ever achieved in such an evaluation,
according to the paper.

Source:
http://www.elektor.com/news/quantum-logic-clock-is-now-world-s-most-precise=
.1272337.lynkx
http://www.nist.gov/public_affairs/releases/logic_clock/logic_clock.html#ba=
ckground
http://arxiv.org/abs/0911.4527


--=20
soliton
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