A team led by the National Institute of Standards and Technology (NIST) recently compared three of the world’s leading atomic clocks and raised the time accuracy of “seconds” to new heights through the air and fiber links. In a paper published March 25 in the journal Nature, the NIST-led study focused on three clocks based on different atoms and linked the most advanced atomic clocks in different locations in the air for the first time.
“These comparisons define the state of technology based on fiber optics and free-space measurements — they are nearly 10 times more accurate than any clock ever made using different atoms,” says NIST physicist David Hume. The new measurements are challenging because the “ticking” frequencies of the three atoms involved are very different. After all, many network components must operate with extreme precision, and wireless links require cutting-edge laser technology and design.
An anatomic clock is a clock that takes the vibration of electrons in an atom as a vibrator, wherein the clock with the electron vibration of the light band as the vibrator is called the light clock. The optical lattice clock is a kind of light clock. The accuracy of atomic clocks makes them an excellent tool for timing and other accurate measurements. This is because atoms emit and absorb photons at a specific frequency, a process largely uninterrupted by environmental factors.
NIST researchers have previously detailed how they transmit time signals over an aerial link between the two clocks, NIST and JILA, and found that the process is as useful as a fiber-based approach, 1,000 times more accurate than traditional wireless transmission solutions. This work shows how the best atomic clocks can be synchronized between remote sites on Earth and time signals are transmitted over long distances, even between spacecraft.
The NIST team measured the frequency ratio, the quantitative relationship between the frequencies of three pairs of atoms. The result is the most accurate measurement of three natural constants ever made. The frequency ratio is considered a constant and is used in some international standards and tests of basic physics theory.
The frequency ratio, as an index for evaluating optical atomic clocks, has important advantages. The direct measurement of optical clock frequencies in the usual hertz units (one cycle per second) is limited by the accuracy of the current international standard, the cesium microwave clock. Frequency ratios overcome this limitation because they are not expressed in any units.
Frequency ratios are usually measured over long distances using optical networks, which are small and far away, or in some cases using microwave data transmitted over satellite links, which are often unstable.