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Science 19 November 2004:
Vol. 306. no. 5700, p. 1307
DOI: 10.1126/science.306.5700.1307
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Introduction to special issue

Higher Standards

Ian Osborne and Daniel Clery

Contents
News
Measurement and the Single Particle
Getting the Measure of Nanotechnology
Time's Romance of the Decimal Point
Putting the Stars in Their Places
In the Blink of an Eye
Viewpoint
Metrology and the State: Science, Revenue, and Commerce
W. J. Ashworth
Reviews
Standards of Time and Frequency at the Outset of the 21st Century
S. A. Diddams, J. C. Bergquist, S. R. Jefferts, C. W. Oates
The Route to Atomic and Quantum Standards
J. Flowers
Quantum-Enhanced Measurements: Beating the Standard Quantum Limit
V. Giovannetti, S. Lloyd, L. Maccone
See related Report by Margolis et al. and Science Express Research Article by Marian et al.
This special issue of Science looks at the development of precision measurement, how its tools have been developed and adapted for better performance, and how the standards used today may be further improved. Historically, measurements were often based on somewhat arbitrary local units. In his Viewpoint, Ashworth (p. 1314) describes, from a British perspective, the development of a standardized metrology as applied to weights and measures and how the burgeoning commerce of the industrial revolution drove its development.

Arguably, today's most important commodity is time. Atomic clocks keep time with an accuracy of about 1 part in 1015 and already have shown applications in everyday life, from navigation to satellite and high-speed optical communications. With a view to improving on this, Diddams et al. (p. 1318) review the progress made with time and frequency standards in the optical regime, where the higher operating frequency offers the possibility of a finer time scale. [See also the Report by Margolis et al. (p. 1355), who show that the transition frequency of a strontium ion can now be determined to within 1 hertz, and the Research Article by Marian (published on Science Express) on using optical frequency combs for precision spectroscopy.]

Exploiting the recognition that the ideal way to count quantities would be in fundamental discrete units, or quanta, was severely hampered by the lack of technology. Standards of the fundamental units were all based on experimental artifacts. With improved technology, combined with improved materials and ingenious engineering, Flowers (p. 1324) reviews the recent progress toward quantum-based standards. Quantum mechanics is one of the most sophisticated tools available. Giovannetti et al. (p. 1330) review theoretical and experimental work on beating the so-called quantum limit. By playing tricks with quantum mechanics, such as using quantum squeezing, they show how measurement can be improved on.

Figure 1 CREDIT: K. BUCKHEIT/SCIENCE
The News pages present a spectrum of the cutting edge of metrology. Andrew Watson describes efforts to turn measurement standards into a counting game: counting atoms to define a kilogram, electrons to define current and capacitance, phonons for temperature, and photons for luminosity (p. 1308). Watson also describes the difficulties facing the semiconductor industry in measuring and reproducing features on chips now that they are down to a few nanometers in size (p. 1309). Atomic clocks are already incredibly accurate, but Robert F. Service found a group that is pushing the decimal point further back with some help from quantum entanglement (p. 1310). The European satellite Hipparcos is the premier metrologist of the heavens, plotting the positions of stars to unprecedented accuracy. Its plot of the position of the Pleiades, however, proved to be a headache, as Govert Schilling found out (p. 1312). In an effort to get a glimpse of lightning-fast processes inside the atom, researchers are striving to create shorter and shorter laser pulses to provide a flash gun. The fastest pulses are now measured in attoseconds: a billionth of a billionth of a second. But, asks Alexander Hellemans (p. 1313), how do you measure a pulse that short?

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