NIST Atomic Fountain Clock Gets Much Better with Time (Forwarded)

National Institute of Standards and Technology
Gaithersburg, Maryland

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September 23, 2005

NIST Atomic Fountain Clock Gets Much Better with Time

The world's best clock, NIST-F1, has been improved over the past few years
and now measures time and frequency more than twice as accurately as it
did in 1999 when first used as a national standard, physicists at the
National Institute of Standards and Technology (NIST) report.

The improved version of NIST-F1 would neither gain nor lose one second in
60 million years, according to a paper published online Sept. 13 by the
journal Metrologia.* NIST-F1 uses a fountain-like movement of cesium atoms
to determine the length of the second. The clock measures the natural
oscillations of the atoms to produce more than 9 billion "ticks" per
second. These results then contribute to the international group of atomic
clocks that define the official world time. NIST-F1 has been formally
evaluated 15 times since 1999; in its record performance, it measured the
second with an uncertainty of 0.53 x 10**-15

The improved accuracy is due largely to three factors, according to Tom
Parker, leader of the NIST atomic standards research group. First, better
lasers, software and other components have made the entire NIST-F1 system
much more reliable and able to operate for longer periods of time. Second,
the atoms in the cesium vapor are now spread out over a much larger volume
of space, reducing the frequency shifts caused by interactions among the
atoms. (The formerly round cloud of atoms is now shaped like a short
cigar.) Third, scientists are now better able to control magnetic fields
within the clock and quantify the corrections needed to compensate for
their effects on the atoms.

Improved time and frequency standards have many applications. For
instance, ultraprecise clocks can be used to improve synchronization in
precision navigation and positioning systems, telecommunications networks,
and wireless and deep-space communications. Better frequency standards can
be used to improve probes of magnetic and gravitational fields for
security and medical applications, and to measure whether "fundamental
constants" used in scientific research might be varying over time -- a
question that has enormous implications for understanding the origins and
ultimate fate of the universe.

* T.P. Heavner, S.R. Jefferts, E.A. Donley, J.H. Shirley, T.E. Parker.
2005. NIST-F1: Recent improvements and accuracy evaluations. Metrologia
(October 2005). Posted online Sept. 13.

IMAGE CAPTION:
[http://www.nist.gov/public_affairs/i...Heavner_LR.jpg
(117 KB)]
NIST researchers (left to right) Steven Jefferts, Elizabeth Donley, and
Tom Heavner with NIST F1, the world's best clock (as of Sept. 2005). The
clock uses a fountain-like movement of cesium atoms to determine the
length of the second so accurately that -- if it were to run continuously
-- it would neither lose nor gain one second in 60 million years.

© 05 Geoffrey Wheeler Photography