ANDREW BROOKES, NATIONAL PHYSICAL LABORATORY / SCIENCE PHOTO LIBRARY ANDREW BROOKES, NATIONAL PHYSICAL LABORATORY / SCIENCE PHOTO LIBRARY
Strontium ion trap being measured. This is the compact strontium ion trap at the UK's National Physical Laboratory, Teddington, UK. This trap is part of a strontium optical clock, also known as a frequency standard. The clock's strontium ions oscillate between two energy levels in response to the light of a laser beam. Counting these oscillations is the basis for the standard second. The international definition of time uses the caesium atomic clock. The strontium optical clock is 100,000 faster than the caesium clock and results announced in 2004 are believed to be three times more accurate than anything previously achieved.
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