Redefining Second with Optical Atomic Clocks | 21 Jul 2025

Source: TH

Researchers have conducted the most precise comparison of optical atomic clocks to date, paving the way to redefine the SI unit of time — the second — by 2030.

• Current Definition of the Second (SI Unit of Time): Since 1967, the second has been defined as 9,192,631,770 cycles of microwave radiation emitted by a Caesium-133 atom, serving as the foundation of global timekeeping through caesium (Cs) atomic clocks.
• Atomic Clocks: An Atomic Clock, invented by Louise Essen in 1955,  is a high-precision timekeeping instrument that measures time using the vibrations of atoms.
  • Atomic clocks don’t directly measure time. Instead, they generate radiation with a fixed frequency (frequency is essentially the inverse of time).
• Optical Atomic Clocks:  They surpass traditional atomic clocks in accuracy, using atoms like Strontium-87, Ytterbium-171, and Indium-115 for 10,000× higher frequency precision. 
  • They use lasers to trigger atomic transitions, producing highly coherent light with stable frequency and wavelength.
• Difference Between Atomic and Optical Clock: Optical clocks can maintain precise timekeeping with a drift of only 1 second over 15 billion years, making them 100 times more accurate than traditional cesium atomic clocks. Cesium atomic clocks lose about 1 second every 300 million years.
  • The cesium clocks operate at a frequency in the microwave range of the electromagnetic spectrum. In contrast, optical atomic clocks function at much higher frequencies in the optical (visible) range, enabling their superior precision.
• Applications of Optical Atomic Clocks: Its potential applications include quantum sensing, high-speed network synchronization, space science, and testing fundamental physics. 
  • In the future, they may even redefine the SI unit of time—the second.