Basic chemistry

What are atomic clocks used for ?

Atomic clock working?


Nobel Prize laureate Norman Ramsey, born in 1915, died at the age of 96. He laid the groundwork for atomic clocks and nuclear magnetic resonance imaging.
Norman Ramsey

What are atomic clocks used for ?

Atomic clock working and applications :

The atomic clocks were developed in the mid-1950s They are based on the laws of quantum mechanics applied to among transitions of levels energy of atoms chosen properly.

Applications of atomic clocks:


Their precision and stability are such that they now constitute time (or frequency ) standards and that is why they are used to define the second since 1967.


It was indeed during the 13 th General Conference of the weights and measures that it was decided that the second was the duration of 9,192,631,770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom .

3.International atomic time(TAI):

Atomic clocks are also used to establish a world time scale, “international atomic time” (TAI).


We are also seeking to develop increasingly precise new atomic clocks to make finer measurements of physical phenomena , for example to test the laws of relativity as we propose to do with the Pharao project  (Clock project atomic by cooling atoms in orbit ).


Atomic clocks were born in the early 1950s. They promise time measurement with extraordinary precision.A drift of less than 1 second every 30 million years.


What synchronize the billions of exchanges that take place almost simultaneously on the Web or satellites at the heart of the GPS system.

In 1956, the International Bureau of Weights and Measures chose to define the second as  “the duration of 9,192,631,770 periods of radiation corresponding to the transition between the hyperfine levels F = 3 and F = 4 of the 6S½ ground state  of the cesium atom 133 “. A sentence which may seem complicated but which can be explained very simply.

Indeed, when a cesium 133 atom receives an electromagnetic wave at a certain frequency , it passes from a state of low energy to a state of higher energy, from state F = 3 to state F = 4 .

 Then, it re-emits the absorbed energy in precisely 1 / 9,192,631,770 seconds . Much like a Comtoise clock counts the oscillations of its pendulum, the atomic clock is there to count the number of these transitions.

Here, the atomic clock with fountain of cesium atoms primary standard of time and frequency of the United States. In 2005, its uncertainty was displayed at 5.10-16 ss-1.
The atomic clock with fountain Of cesium atoms

How an atomic clock works?

An atomic clock consists of a cesium furnace which generates a very directive jet of cesium atoms. On the path of these atoms, a device – magnetic deflection ( magnets ) or optical pumping – makes it possible to select those which are in the level of energy sought, the state F = 3.

Then there is a resonant cavity, called Ramsey , in which the atoms interact with a microwave generated by a quartz oscillator – electric signal with frequency 9,192,631,770  Hz .

Finally, a detection device (magnet, ionizer and electron multiplier or laser and photo detector) provides information on the atoms that have actually undergone the expected transition. The system then modifies the frequency of the quartz to arrive at a maximum number of atoms in the state F = 4.

Finally, the operation of a cesium jet atomic clock:

Finally, the operation of a cesium jet atomic clock is based on a quartz oscillator. Cesium atoms play the simple role of controllers and adjusters of the frequency of the signal generated by quartz (there are also, for example, rubidium clocks , less efficient or hydrogen clocks , extremely effective on the short term).

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