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The International System of Units (SI) has illuminated scientific measurement since 1795 when the first six SI prefixes were introduced. These ranged from mega (10^6) to milli (10^-6) and served scientists well for almost two hundred years.

In 1960, however, the International Bureau of Weights and Measures which standardises and regulates the system, decided that a greater range of prefixes were needed and introduced the tera (10^12), giga (10^12), nano (10^-9) and pico (10^-12) prefixes. Since then, this organisation has introduced various new prefixes at either end of the scale culminating with the introduction of the yotta (10^24) and yocto (10^-24) prefixes in 1991.

These most recent prefixes have yet to be widely used but that looks set to change with the announcement today by Michael Biercuk and buddies, at the National Institute of Standards and Technology in Boulder Colorado, that they’ve built a device capable of detecting yoctonewtons.

Their kit consists of a few dozen beryllium ions trapped in magnetic and electric fields using a device called a Penning trap. These ions vibrate at between a few mega and kilohertz, frequencies that can be accurately measured by bouncing laser light off the ions and measuring any Doppler shift they cause.

Being charged, the ions are highly susceptible to the effects of stray magnetic and electric fields which change the frequency at which they vibrate. It turns out, say Biercuk and co, that this system can measure forces from these stray fields that are only a few dozen yoctonewtons in strength. In fact, the smallest force they measured was 174 yoctonewtons using a trap holding about 60 beryllium ions.

And they say that with straightforward modifications, they should soon be able to measure a single yoctonewton using an individual ion.

What’s impressive about the work is that these force measurements are three orders of magnitude better than anything that has been possible before. The most sensitive force detectors until now have been resonating spring boards that are capable of measuring attonewtons (atto=10^-18).

The new technique suddenly allows physicists to measure much tinier forces than ever before. A step change like this should immediately solve various unanswered questions in materials science. Of course, the question is what kinds of problems are waiting for this kind of sensitivity? Suggestions below, if you have any.

It also means that International Bureau of Weights and Measures urgently needs to meet and decide on the prefixes that come after yocto that will represent 10^-27 and 10^-30.

Ref: arxiv.org/abs/1004.0780: Yocto-Newton Force Detection Sensitivity Using Trapped Ions


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