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Precise futuristic timekeeping with optical lattice clocks

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Posted April 1, 2015
This news or article is intended for readers with certain scientific or professional knowledge in the field.

A research group, led by Professor Hidetoshi Katori (Chief Scientist, RIKEN) at the University of Tokyo Graduate School of Engineering has developed a pair of atomic clocks that agree with respect to each other at a fractional uncertainty of 2×10-18. This means they will be out of synchronization by just one second every 16 billion years. The clocks are based on optical lattice clock that performs the superb high-precision spectroscopy of thousands of atoms in a cold environment. This record-high agreement of the two clocks demonstrates an important leap in fundamental technology that facilitates the use of optical lattice clocks in a future redefinition of the second.

a. Statistical uncertainty of frequency difference of 2 cryo-clocks (Allan st. dev.) reaches 2x10-18 averaging time 2 hours. b. Observed frequency differences of 2 cryo-clocks. Individual frequencies (about 429x1012 Hz) do not deviate by more than several mHz. Averaging 11 measurements over 1 month 2 clocks agree within Δν/ν0=(-1.1±2.0)x10-18. Shaded area: systematic uncertainty of 4.4x10-18 experimentally evaluated for 2 clocks. Image credit: Hidetoshi Katori

a. Statistical uncertainty of frequency difference of 2 cryo-clocks (Allan st. dev.) reaches 2×10-18 averaging time 2 hours. b. Observed frequency differences of 2 cryo-clocks. Individual frequencies (about 429×1012 Hz) do not deviate by more than several mHz. Averaging 11 measurements over 1 month 2 clocks agree within Δν/ν0=(-1.1±2.0)x10-18. Shaded area: systematic uncertainty of 4.4×10-18 experimentally evaluated for 2 clocks. Image credit: Hidetoshi Katori

Currently, optical lattice clocks are being developed all over the world aiming at nearly 1000 fold improvement in uncertainty over the international atomic time (TAI) based on microwave cesium clocks. A major challenge in improving the uncertainty of optical lattice clocks is to eliminate the influence of electromagnetic waves radiated from the surrounding walls at room temperature (blackbody radiation), which changes the eigen-frequency of atoms. To address this issue, the research group have developed cryogenic optical lattice clocks where strontium atoms are interrogated in a cryogenically-cooled environment at -180 degrees Celsius, reducing the influence of blackbody radiation by 1/100. A comparison between two such cryo-clocks over a period of one month has yielded a statistical agreement of 2×10-18.

Realization of such a high-precision atomic clock is a step forward towards the redefinition of the second, and holds potential for new roles that are radically different from conventional clocks. It is possible to detect relativistic time delay caused by gravitational potential difference of few centimeters height difference between two clocks, which leads to “relativistic geodesy technology” to measure the height difference between two remote places. Furthermore, such high-precision clocks can be probes for New Physics, for example by investigating the constancy of physical constants comparing two clocks consisted of different atomic elements.

Source: University of Tokyo

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