Optical Atomic Clock 

Syllabus: GS3/ Science and Technology

Context

• Researchers from six countries have conducted the world’s largest and most accurate comparison of optical atomic clocks across three continents. 
• It is a major step towards redefining the SI unit of time — the second — using optical clocks instead of current caesium-based atomic clocks.

What is the Current Definition of a Second?

• Present Standard (since 1967): One second equals the time taken for 9,192,631,770 cycles of radiation produced by the caesium-133 atom when it changes between two energy states.
  • Caesium was chosen for its high accuracy and consistency.
• India’s Timekeeping: The National Physical Laboratory (NPL) in Delhi maintains India’s time standard using five caesium clocks.
  • The clocks’ output is disseminated to various applications around India via the INSAT satellites, telecommunication signals, and fibre links.

What are Optical Atomic Clocks?

• Like caesium clocks, Optical Atomic Clocks measure time based on an atom’s internal energy transitions, but use optical (visible light) frequencies instead of microwaves.
• Common Atoms Used in Optical Clocks: Strontium-87 (Sr), Ytterbium-171 (Yb) and Ytterbium ions (Yb⁺), Indium-115 ions (In⁺) and Charged Strontium-88 (Sr⁺).

Why Replace Caesium with Optical Clocks?

• Higher Frequency, Better Precision: Optical clocks use higher-frequency visible light, enabling more oscillations per second and thus more precise time measurement than caesium clocks.
  • Caesium clocks use radiation at 9.19 billion Hz,
  • Strontium clocks use 429 trillion Hz,
  • Ytterbium clocks use 642 trillion Hz.
• Unmatched Stability: Some optical clocks are so stable that they drift by just one second in 15 billion years, making them 10,000 times more precise than caesium clocks.
• Atomic Transition Principle : Like caesium clocks, optical clocks measure time by counting how atoms shift between fixed energy levels.
  • But instead of microwaves, they use lasers to stimulate and detect these shifts, resulting in much more stable and accurate frequency measurements.

Significance of the Development

• Lays Foundation for Redefining the Second, likely by 2030.
• Supports High-Precision Applications like:
  • Satellite navigation (GPS, NavIC, Galileo)
  • Radio astronomy (e.g., black hole imaging)
  • Climate science (tracking gravity changes due to ice/water loss)

Source: TH