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New Portable Atomic Clock Offers Very Accurate Timekeeping at Sea

Atomic clocks are the backbone of the Global Positioning System (GPS), the network of satellites above the earth that we use every day to navigate cities, respond to emergencies, and organise military operations, among other things. Despite being one of the most accurate timekeeping methods, however, there is still room for improvement. Scientists today are pushing the boundaries with a new technology called optical atomic clocks.

The Working of An Atomic Clock

Atomic clocks work by keeping time using atoms. One popular design uses atoms of an isotope of caesium, Cs-133. The International Committee for Weights and Measures first used it in 1967 to define the duration of one second. India also uses a Cs-133 atomic clock to define the second for timekeeping within its borders.

  • Cs-133 is a highly stable atom and is found naturally, which is why it is so commonly used in atomic clocks.
  • Atomic clocks exploit a fundamental property of all atoms: their ability to jump between different energy levels. Energy levels are like the steps of a ladder. An atom climbs up the ladder by absorbing energy, like electromagnetic radiation.
  • In a Cs atomic clock, the energy needed for the atom to jump to a higher energy level matches the frequency of microwave radiation. This frequency is related in some fully understood way to the duration of a second.
  • The Cs-133 atoms absorb this radiation and jump to a higher energy level. This transition only happens when the frequency of the applied radiation is equal to 9,192,631,770 Hz.

How optical Atomic Clocks are different?

Optical atomic clocks are even more accurate. While they have the same working principle, the resonance frequency here is in the optical range. Radiation in this range includes visible light (to humans) and ultraviolet and infrared radiation. As part of an optical atomic clock, researchers use lasers to stimulate atomic transitions. The lasers’ light is highly coherent: the emitted light waves all have the same frequency and their wavelengths are related to each other in a way that doesn’t change. The result is light with more precise properties and great stability. Optical atomic clocks use coherent light to achieve higher accuracy in two main ways. The first is the higher operating frequency of atomic clocks. Say we have two clocks, A and B. A has a higher operating frequency than that of B, which means A will complete more oscillations than B in the same time.

Optical atomic clocks at sea

The researchers conducted initial tests at the U.S. National Institute of Standards and Technology (NIST) in April 2022. They operated two prototypes, called PICKLES and EPIC, autonomously for 34 days. The optical atomic clocks’ accuracy fluctuated less over short periods, outperforming NIST’s hydrogen maser ST05, one of the world’s most accurate and stable atomic clocks, which is based on hydrogen atoms.


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