An experimental atomic clock based on a single mercury atom is now at least five times more precise than the national standard clock, according to a paper by physicists at the NIST in the July 14 issue of Physical Review Letters*. The experimental clock, which measures the oscillations of a mercury ion (an electrically charged atom) held in an ultra-cold electromagnetic trap, ticks at "optical" frequencies-much higher than the microwave frequencies measured in cesium atoms in NIST-F1, the national standard and one of the world's most accurate clocks. Higher frequencies allow time to be divided into smaller units, which increases precision.
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