Accuracy’s secret ingredient

The world’s most accurate clock doesn’t just improve on efforts to measure time, it out-performs previous title-holders by a factor of ten.

NIST's ultra-stable ytterbium lattice atomic clock.  Credit: Burrus/NIST

While atomic clocks have long been regarded as the world’s most accurate, US scientists at the National Institute of Standards and Technology (NIST) have dramatically improved the breed in recent months with a timepiece made from the barely pronounceable material ytterbium.

Ytterbium is a soft and pliable rare earth element which was first discovered by the Swiss chemist Jean Charles Galissard de Marignac. It is usually extracted from monazite sand and is also mined in Australia. Ytterbium is also used in an alloy as a non-toxic tooth filling. The material does not have a wide application in the commercial world.

The ytterbium clock uses 10,000 rare-earth atoms cooled to 10 micro-kelvin (10 millionth of a degree above zero) which are fixed in an optical lattice made of laser light. In other words it’s not something you could assemble at home, which is how early clocks were made. Under development for more than a decade, it has a ticking rate that varies less than two parts in one quintillion, making it accurate to a few tens of quadrillionths of a second, or one second in 300 million years.

Pictured above: NIST’s ultra-stable ytterbium lattice atomic clock. Credit: Burrus/NIST

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