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Author Topic: How does an atomic and an optical clock work? How do they differ?  (Read 435 times)

Offline chris

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I was investigating this question for my own education and came across this reference, which is, in my opinion an excellent piece of writing that manages to be both clear and succinct and also detailed. Credit where credit is due to the author:

http://spectrum.ieee.org/aerospace/satellites/introducing-the-worlds-most-precise-clock

However, if anyone would like to elaborate more on the topic, or bring us even more up to date, that would be most welcome!

Chris


 

Offline evan_au

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I felt that article was a good summary.

Some of the recent experimental optical-lattice clocks are said to be stable enough to detect a 2cm change in height - purely due to the change in gravitational time dilation!

But the best ones require cooling down to 0.00001 Kelvin. That sort of cooling is not easily compressed into a wristwatch!

See: https://en.wikipedia.org/wiki/Atomic_clock#Optical_clocks
 

Offline evan_au

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I had a chat to a friend working in Australia's National Measurement Institute.
  • NMI use commercial Cesium clocks; these cost about $US70,000, and need refurbishment after 10 years for about $US30,000.
  • You can obtain Rubidum atomic clocks for $1,000 - $2000 (and even cheaper, second-hand).
  • There are now commercial trapped ion clocks. But the international standard is currently based on Cesium clocks.
  • Transfer of time reference around the nation and international is done by both ends of the transfer observing the same individual GPS satellites, while they are visible in both locations. This is more accurate than the normal GPS-based time reference, which is an average of the time provided by a group of satellites - but each location will see a different set of GPS satellites.
  • For time transfer to the other side of the Earth, both laboratories can't observe the same GPS satellite at the same time, so it is done in two hops, using an intermediate laboratory with a Cesium clock.
  • Most of our computers and smartphones have their time set by Network Time Protocol (NTP), and some NTP servers are synchronized by this method.

For a specialist time-keeping interest group, see: http://www.leapsecond.com/time-nuts.htm
In case you want your own atomic clock at home, apparently they have instructions for obtaining your own Rubidium clock on the cheap by resurrecting defunct Rubidium tubes!
 

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