Optical Atomic Clocks Set To Redefine The Second
The world is on the verge of redefining the second, the fundamental unit of time, using cutting-edge optical atomic clocks. These devices surpass the current caesium atomic clocks in precision and stability. A recent global collaboration involving 10 optical clocks across three continents has successfully demonstrated unprecedented agreement in time measurement. This milestone strengthens confidence in adopting optical clocks as the new international time standard by around 2030.
Evolution of the Second
The second was originally defined as a fraction of the Earth’s rotation and revolution. Early 20th-century definitions used the solar day and the Earth’s orbit. Quartz clocks in the mid-1900s improved accuracy beyond Earth’s movements. In 1967, the second was redefined using the frequency of radiation emitted by caesium-133 atoms. This atomic standard measures 9,192,631,770 cycles per second, providing remarkable precision.
Working Principle of Caesium Atomic Clocks
Caesium atomic clocks use microwave radiation to induce energy transitions in Cs atoms. The clock adjusts the microwave frequency to maximise transitions, locking it at exactly 9,192,631,770 Hz. Frequency dividers count these cycles to mark one second. Many countries maintain such clocks to define national time standards. These clocks underpin technologies like GPS and telecommunications.
Limitations of Caesium Clocks and Need for Optical Clocks
While caesium clocks lose only one second every 300 million years, some applications demand even higher precision. Optical atomic clocks measure frequencies in the optical range, about 10,000 times higher than microwaves. For example, strontium and ytterbium atoms emit radiation at frequencies exceeding 400 trillion Hz. This allows measuring time to the 18th decimal place, with stability that could keep accurate time for billions of years.
Global Comparison of Optical Clocks
A landmark test involved 10 optical clocks using different atoms, located in Finland, France, Germany, Italy, the UK, and Japan. Clocks were linked by optical fibres and advanced GPS techniques to compare frequencies. The test ran continuously for 45 days in 2022. Researchers measured 38 independent frequency ratios, including four never measured before. Results showed agreement within factors of 10^-16 to 10^-18, confirming the clocks’ remarkable precision.
Challenges and Future Steps
The test revealed minor discrepancies such as signal glitches and small frequency offsets between clocks. These must be resolved before redefining the second internationally. Researchers developed statistical tools to handle correlated errors in data from shared equipment and links. The success of this large-scale comparison validates the feasibility of a new time standard based on optical clocks, promising enhanced precision for science and technology.
Applications of Ultra-Precise Timekeeping
Atomic clocks are vital for GPS, satellite navigation, radio astronomy, and climate science. Optical clocks will improve these fields by providing more stable and accurate timing. For example, they can detect subtle changes in Earth’s gravity or improve synchronization in global networks. The redefinition of the second will impact multiple industries relying on exact time measurement.
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