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How Does an Atomic Clock Work?

08/04/2024 | JSA Support

The maximum amount of error that an atomic clock can make is 1 second. That too in up to 100 million years! That is the extent of its accuracy.  The reason for this accuracy is that an atomic clock measures the precise length of a second. A second is the base unit of timekeeping and is defined as the time taken for a Caesium-133 atom to oscillate 9 billion, 192 million, 631 thousand, and 770 times! It makes you wonder how does an atomic clock work to achieve all this. There is only one way to find out: read ahead!

The Difference Between Atomic Clocks and Regular Clocks?

We have all had to re-sync our clocks and watches from time to time as they eventually detract from the actual time. This is precisely where atomic clocks differ from regular clocks. An atomic clock does not make mistakes or require you to sync it with the correct time over and over again (other than once in many billion years!). They are designed to keep time extremely precise to avoid making frequent adjustments.  The reason these clocks are called atomic clocks is because they keep time by tracking the oscillations of different atoms which happens at a much higher frequency and a constant and stable rate.

Atomic clocks are extremely crucial time-measuring devices that ensure the accurate calculation of International Atomic Time or TAI. They are also used to measure the Coordinated Universal Time (UTC) as well as the local times around the world. This makes these timekeeping devices not just extremely precious but also quite expensive.

Atomic Clocks: How Do They Work?

Although there are various types of atomic clocks, they all have the same working mechanism.  Atomic clocks track the precise oscillations of specific atoms to measure time. You can imagine these atomic oscillations as the movement of a pendulum in a grandfather clock.

1.     Treating The Atoms

The atoms involved in an atomic clock are found in two different states known as hyperfine levels. You can think of these states as state A and state B for ease. The atoms are first heated in a microwave and organized into a singular beam. Using a magnetic field, atoms in state B are filtered out from the beam so it only contains atoms in state A.

2.     Irradiation and Counting

The beam containing atoms in state A is passed through a resonator where the atoms experience microwave radiation. This causes some of the atoms in state A to switch to state B. Coming out of the resonator the atoms are subjected to another magnetic field which filters the remaining state A atoms from the beam. The beam of atoms then moves to a detector which counts the atoms that have been switched to state B.

3.     Tuning

The percentage of atoms that change their state in the resonator depends on the frequency of the microwave radiation. The greater the synchronization there is between the atoms’ oscillations and the microwave radiation frequency, the more atoms are likely to switch states. The purpose of this exercise is to tune the microwave radiation frequency to the atoms’ oscillations to measure time (9 billion, 192 million, 631 thousand, and 770 oscillations amounting to the passing of a single second)

Frequently Asked Questions

Q1. What are the types of atomic clocks?

There are different types of atomic clocks depending on the atom being used including cesium atomic clock, hydrogen atomic clock, and rubidium atomic clock. The most accurate and commercially used of these is the one using the cesium atom.

Q2. How accurate are atomic clocks?

Atomic clocks are extremely accurate with the largest error possible of a single second in 1000 million years. One of the strongest atomic clocks which uses the strontium atom is accurate up to 1/15,000,000,000 of a second per year. 

Q3. How many atomic clocks are there in the world?

There are about 400 atomic clocks in the world supporting the International Atomic Time (TAI) scale and precisely keeping time.


Now that you have learned how does an atomic clock work, you may want to get one for yourself. Having an atomic watch as part of your watch collection can be quite a prestigious thing. These atomic time measuring devices can raise your image and esteem at any important gathering. So, if you are ready to invest in an atomic clock, you will find several outstanding options at Arizona Fine Time!