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https://physics.stackexchange.com/questions/450654/how-atomic-clock-works/726135#726135[How atomic clock works? answer] by <Ciro Santilli> on <Physics Stack Exchange>.

\Video[https://www.youtube.com/watch?v=p2BxAu6WZI8]
{title=How an atomic clock works, and its use in the global positioning system (GPS) by <EngineerGuy> (2012)}
{description=Shows how conceptually an atomic clock is based on a <feedback loop> of two <hyperfine structure> states of <caesium> atoms (non-<radioactive> <caesium-133> as clarified by the <Wikipedia> page). Like a <quartz clock>, it also relies on the <piezoelectricity> of quartz, but unlike the <quartz clock>, the <quartz> is not shaped like a <tuning fork>, and has a much larger resonating frequency of about 7 <MHz>. The feedback is completed by producing <photons> that <resonate> at the right frequency to excite the <caesium>.}

\Video[https://www.youtube.com/watch?v=eOti3kKWX-c]
{title=Inside the <HP> 5061A Cesium Clock by <CuriousMarc> (2020)}
{description=
A similar model was used in the <Hafele-Keating experiment> to test <special relativity> on two planes flying in opposite directions. Miniaturization was key.

Contains a disposable tube with 6g of <Caesium>. You boil it, so when it runs out, you change the tube, 40k USD. Their tube is made by <Agilent Technologies>, so a replacement since that opened in 1999, and the original machine is from the 60s.

Detection is done with an <electron multiplier>.

https://youtu.be/eOti3kKWX-c?t=1166 They compare it with their 100 dollar <GPS> disciplined oscillator, since <GPS> <satellites> have <atomic clocks> in them.
}

\Video[https://www.youtube.com/watch?v=Tc_tDVbjCQk]
{title=Quick presentation of the <atomic clock> at the <National Physical Laboratory> (2010)}
{description=Their super accurate setup first does <laser cooling> on the <caesium> atoms.}


Atomic clock

{c}
{title2=1867-1934}
{wiki}

= Pierre and Marie Curie
{c}
{synonym}

Like all big names in science, she was at the right place at the right time and with the right interest and passion.

Notably, the man she married, <Pierre Curie>, happened to be a the world master at precisely the technique that she needed to carefully measure <radioactivity>: he had the most precise <electrometers> in the world, which allowed to detect small amounts of <radioactivity> via the <ionization of air by radiation >. These used <piezoelectricity>, which <Pierre Curie> co-discovered with his brother.

\Video[https://youtu.be/wbuDmY5gpXQ?t=1566]
{title=<Marie Curie> section of <The Mystery of Matter> episode 2}
{description=
Fantastic illustration of Marie's life and work!
* https://youtu.be/wbuDmY5gpXQ?t=2041 she specifically avoided <X-ray> research because she felt that there was too much competition in that area. TODO find a written reference about that and add it to Wikipedia.
}

\Image[https://upload.wikimedia.org/wikipedia/commons/c/c8/Marie_Curie_c._1920s.jpg]
{title=<Marie Curie> c. 1920}
{height=600}


Marie Curie

{wiki}

\Video[https://www.youtube.com/watch?v=_2By2ane2I4]
{title=How a quartz watch works by <Steve Mould> (2017)}
{description=Mentions <feedback loop> loop with the <quartz> <tuning fork> for the <piezoelectricity> and an <amplifier>. Also mentions the choice of 32768 <Hertz> ($2^{15}$) as the first power of 2 that is outside of the <human hearing range>, and then how a <frequency divider> is used to reduce the frequency to get the <second> counter.}


Ciro Santilli @cirosantilli 36

 Incoming links: Piezoelectricity