How does an atomic clock work? How does it start telling extremely precise time?
In: Technology
An atomic uses a clump of atoms of a pure element. When excited, these atoms vibrate at a specific frequency that depends on the element’s electron alignments. By counting the vibrations, you can get a very precise clock that’s stable over a long time period.
Real atomic clocks use some gas of a specific element, like caesium or rubidium. The element has a natural resonance frequency, which means it interacts most strongly with microwaves of a specific frequency.
You stick the gas in a box and beam microwaves at it. You can then detect how strongly the gas interacts with the microwaves (e.g. by producing more microwaves or absorbing them, depending on the design). So you have a circuit generate the microwaves at an adjustable frequency, and then you have another circuit basically “tune” the first one until it finds the best frequency, much like you would manually tune a radio to a station until you get the best reception. After a while the whole thing slowly becomes very stable when the right frequency is found and narrowed down.
To count seconds, you have a third circuit just divide down the microwave signal. Since you know the frequency at which the gas should resonate, you just count up to that number and every time you reach it, a second has passed.
The store-bought clocks you find labeled “atomic clocks” are just normal clocks with a radio receiver that picks up time signals sent by a radio station that itself has a real atomic clock.
OP – you are not asking about the “atomic clocks” that sit on a desktop or a nightstand, are you? If you are, those DO NOT have a cesium atom vibrating inside.
Those clocks actually have radio receivers that listen for data transmission by NIST (in the U.S.). Those radio transmissions are linked to the NIST atomic clocks which DO have a cesium atom vibrating inside.
Side note – I have 3 different desktop “atomic clocks”, no two of which display the same time, and none of which displays the correct time. Admittedly, they are all quite old – 15-20 years.
Just to add to this but from my limited market experience with high precision clocks an atomic clock is mostly used as a backup for a GPS clock.
Follow up question: How do you set an atomic clock? Say a city buys a new one, how do they set it to a time that they know is ‘correct’?
I think there’s also atomic clocks located in different countries of the world and sometimes they compare the time between them to see if there are any errors.
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