Optical lattice atomic clock could 'redefine the second'

By Rebecca Morelle
Science reporter, BBC World Service

Optical lattice clock
Image caption,
The optical lattice clock shines lasers on atoms to measure time

Scientists say they have found a more accurate way to measure time.

We currently use atomic clocks to count the seconds, but tests on an alternative atomic timekeeper have revealed that it is more precise.

The devices, called optical lattice clocks, lost just one second every 300 million years - making them three times as accurate as current atomic clocks.

Writing in Nature Communications, the team said they offered a better system for defining the second.

Laser show

We once used the Earth's rotation to measure time, where one spin equates to a day.

But because our planet wobbles on its axis as it rotates, some days can be shorter or longer than others.

The atomic clock has proved to be a far more accurate method of keeping the world on time and since the 1960s has been used to define a second in the International System of Units (SI units).

But now scientists say the optical lattice clock could improve the precision.

Just as a grandfather clock uses the swing of a pendulum to measure intervals of time, an atomic clock uses the very regular "vibrations" of atoms.

Our current systems, called caesium fountains, expose clouds of caesium atoms to microwaves to get them to oscillate. But the new ones use light to excite strontium atoms.

Dr Jerome Lodewyck, from the Paris Observatory, said: "In our clocks we use laser beams. Laser beams oscillate much faster than microwave radiation, and in a sense we divide time in much shorter intervals so we can measure time more precisely."

Image caption,
The researchers believe the new clock could be used as a standard for the world's time

The optical clocks are three times as accurate as caesium fountains, which are accurate to one second every 100 million years.

As well as comparing the optical lattice clocks with our current atomic timekeepers, the researchers compared two optical clocks with each other. They found that they kept time in agreement, and were also very stable.

"For instance, if you have your wristwatch, and one day you are one second late, and one day one second early, then your clock is not stable. But it could still have good accuracy if over a million days the time is correct," Dr Lodewyck explained.

It is important to measure both accuracy and stability, he added.

Many technologies such as telecommunications, satellite navigation and the stock markets rely on ever-better time measurements. The researchers said the new clocks could one day help to redefine the second.

Another clock is also undergoing development - an ion clock. This clock loses just one second every few billion years, but because it relies on a single ion, it is not yet deemed to be stable enough for widespread use.

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