International Atomic Time (TAI) is a high-precision atomic coordinate time standard based on the hypothetical passage of appropriate time on Earth’s geoid.  It is a time scale that does not include leap seconds. It is the most important manifestation of Terrestrial Time (with a fixed offset of epoch). It also serves as the foundation for Coordinated Universal Time (UTC), which is utilised for civil timekeeping across the globe. UTC differs from TAI by a few hundredths of a second. UTC is exactly 37 seconds behind TAI as of January 1, 2017, when another leap second was implemented. The 37 seconds are the result of a 10-second difference at the beginning of 1972, plus 27 leap seconds in UTC since 1972.
How does it work?
The inherent oscillations of atoms work like the pendulum of a grandfather clock in an atomic clock. Atomic clocks, on the other hand, are significantly more precise than ordinary clocks due to the much higher frequency and stability of atomic oscillations.
Although there are many distinct types of atomic clocks, they all work on the same basic concept, which is outlined below:
Sort, heat, and bundle
The atoms are first heated in an oven before being bundled into a beam. Each atom can exist in one of two energy states. They’re known as hyperfine levels, but we’ll name them to state A and state B for now.
All atoms in state B are then removed from the beam by a magnetic field, leaving just atoms in state A.
Count and Irradiated
The state-A atoms are passed through a resonator and exposed to microwave radiation, which causes some of them to shift to state B. A second magnetic field is used behind the resonator to eliminate atoms that are still in state A. The number of atoms that have transitioned to state B is then counted by a detector.
Measure and Tune
The frequency of microwave radiation determines the percentage of atoms that change state while passing through the resonator. The closer it is to the atoms’ natural oscillation frequency, the more they change their state.
The idea is to fine-tune the microwave frequency to the atoms’ oscillations before measuring it. A second has passed after exactly 9,192,631,770 oscillations.
Accuracy of atomic clock
Atomic Clocks are becoming more accurate day by day, The NIST-F1 in Boulder, Colorado, is one of the world’s most precise clocks, with an expected inaccuracy of only 1 second every 100 million years.
Lasers concentrate the atoms into a cloud, cool them down, and then toss them skyward in a caesium fountain clock. This method slows down the atoms, allowing for a longer measuring period and a more accurate estimate of the atoms’ intrinsic frequency.
Optical Clocks are a type of clock that uses light to tell time.
Scientists are currently working on a technology that will be even more precise than today’s atomic clocks. The optical atomic clock measures atomic oscillations using light in the visible spectrum. Light rays have a resonance frequency around 50,000 times greater than microwave radiation, allowing for more exact measurements. The new optical clock’s estimated variance is 1 second per 15 billion years.
What is the need for atomic clock
International Atomic Time (TAI), one of the time standards used to determine Coordinated Universal Time (UTC) and local times around the world, is calculated using 400 atomic clocks around the world.
Satellite navigation systems such as GPS, GLONASS, and Galileo rely on exact time measurements to derive precise positions.
Difference between daily clock and atomic clock
Anything that can count time is referred to as a clock. Different types of clocks include water clocks, mechanical clocks, electronic clocks, and atomic clocks.
Every modern clock contains an oscillator, which alternates between two states on a regular basis. It is the pendulum that swings back and forth in a pendulum clock. The escapement sings from one side to the other in a mechanical watch. It is the vibrations of a quartz crystal in an electronic watch.
The oscillation frequency of an atomic clock is the atom’s resonant frequency. Rubidium, for example, has exceptionally constant resonance frequencies. An atomic clock, instead of counting the swings of a pendulum, counts the oscillations of a rubidium atom.