What is atomic clock?

 Have you wondered how time works?  What do you mean by 1 sec?  How the duration of 1 sec is decided?
All these questions will be answered when you understand the atomic clock. World time is based upon a reference and that reference is the atomic clock. 

What is atomic clock

An atomic clock is a clock device that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element. i.e. locking an electronic oscillator to the frequency of an atomic transition. The transition is generally between hyperfine level which is a small shifts and splittings in the energy levels of atoms resulted from interaction between the magnetic moments associated with electron spin and the electrons' orbital angular momentum.

Elements used for atomic clock

1. Cesium-133

2. Rubidium-87

Cesium atomic clock

It employ a beam of cesium atoms. The clock separates cesium atoms of different energy levels by magnetic field.

Rubidium Atomic clock

It is the simplest and most compact of all, use a glass cell of rubidium gas that changes its absorption of light at the optical rubidium frequency when the surrounding microwave frequency is just right.

The most accurate atomic clocks available today use the cesium atom and the normal magnetic fields and detectors. In addition, the cesium atoms are stopped from zipping back and forth by laser beams, reducing small changes in frequency due to the Doppler effect.

Cesium is chosen for atomic clock because of the advantage of its atomic structure. It has lone electron in its outermost shell which has hyperfine structure because of nuclear spin. It needs microwave frequency(very small energy) to have a hyperfine level transition. The frequency needed for he transition is accurately determined in case of cesium and it is easily reproducible using frequency oscillator.

Because of high accuracy of atomic clock, the astronomical time base has been scraped and a new standard has been evolved. We define 1 second as

The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

 i.e.  1 second = 9,192,631,779 cycles of standard Cs-133 transition

We can say that 9,192,631,779 Hz frequency is needed for Hyperfine level transition in standard Cs-133 atom. This frequency has been accurately determined and precisely reproduced.  

It has been claimed that the best atomic clock gives an uncertainty of 1 second in 30 million years.

New researches are being carried out which is claiming to be 100 times more accurate then the best atomic clock. A newly proposed clock that uses the orbit of a neutron around an atomic nucleus to keep time would be so accurate that it would only gain or lose 1/20th of a second every 14 billion years – or about the lifetime of the universe.