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New Optical Single-Ion Clock Is Most Accurate Timepiece Ever Built

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A new optical single-ion clock in Germany has now dethroned JILA's optical lattice atomic clock as the world's most accurate timepiece ever built.

With an unprecedented level of accuracy, the optical single-ion clock works by measuring the vibrational frequency of ytterbium ions as they swing back and forth hundreds of trillions times per second.

The ytterbium ions are trapped within an optical "web" of laser beams that allows physicists to count the number of "ticks" per second, determining time so accurately that the single-ion clock won't gain or lose a second in several billion years.

Prior to the development of the ytterbium-ion clock, the most accurate time-keepers were made of caesium. These optical lattice atomic clocks contained a "pendulum" of atoms that are excited by microwave radiation. The official definition of the second is based on these clocks.

According to the most accurate caesium clocks, one second is the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the caesium atom.

However, when it comes to defining time, one can never be too accurate. Scientists all over the world have been attempting to perfect their optical atomic clocks, and so the need to redefine the "second" is becoming important.

Now, Germany's Physikalisch-Technische Bundesanstalt (PTB) has ousted the most accurate caesium clocks by building their own optical atomic clock, which is 100 times more accurate.

"It is regarded as certain that a future redefinition of the SI (International System of Units) second will be based on an optical atomic clock," the physicists wrote. Optical atomic clocks are much more accurate and stable than caesium clocks because of their considerably high excitation frequency of 1E14 to 1E15 Hz.

During the 1980s, Nobel Prize award-winning physicist Hans Dehmelt predicted the eventual development of optical clocks. These devices are basically laser traps for neutral atoms or single ions.

Many atomic clocks have been developed in the past, but the PTB team's single-ion clock is the first to achieve an accuracy level that had only been calculated in theory.

Ytterbium, a soft and silvery chemical element, is perfect for the clock because it can move between states to produce a clear and measurable "tick," researchers said.

The team's findings are featured in the journal Physical Review Letters.

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