The latest development, at NIST, on Atomic Clocks might result in a redefinition of Second, the international unit of time.

A clock device that uses an Electron Transition Frequency in the Optical, Ultraviolet, and Microwave region of the electromagnetic spectrum of atoms for its timekeeping element is called an Atomic Clock. They are the most accurate frequency and time standards known to humanity. As a result, they are used as primary standards for global time distribution services. Similarly, they are used to control the frequencies in television broadcast and GPS.

The exceptional accuracy of these clocks allows them to achieve some amazing performance records. According to a recent study, published in the journal ‘Nature’, experimental atomic clocks at the National Institute of Standards and Technology (NIST) have achieved some new records.

Each of these clocks traps a thousand Ytterbium atoms in optical lattices. Continuous switching between two energy levels is the source of ticking for these atoms. Researchers compared two independent clocks and found their ticking to be so precise that it could detect the faint signals from the early universe, gravity, and even dark matter.

The physicists from NIST explained that the three performance records were achieved in Stability, Systematic Uncertainty, and Reproducibility. Stability refers to the changes in a clock’s frequency over a specified time interval. The calculations revealed that they were at 3.2 parts in 10¹⁹ over a day. Systematic Uncertainty measures how well the clock represents the frequency of the atoms.

Physicists at NIST found that a possible error of 1.4 parts in 10¹⁸ was possible in this regard. Similarly, Reproducibility shows how closely the two clocks tick at the same frequency. The analysis showed that the frequency difference was less than 10^-18. Andrew Ludlow, the Project Leader at NIST, talked about the importance of these measures and said,

“Systematic uncertainty, stability, and reproducibility can be considered the ‘royal flush’ of performance for these clocks. The agreement of the two clocks at this unprecedented level, which we call reproducibility, is perhaps the single most important result because it essentially requires and substantiates the other two results. This is especially true because the demonstrated reproducibility shows that the clocks’ total error drops below our general ability to account for gravity’s effect on time here on Earth. Hence, as we envision clocks like these being used around the country or world, their relative performance would be, for the first time, limited by Earth’s gravitational effects.”

The levels of reproducibility shown in this latest paper are unprecedented and that’s the reason why Ytterbium clocks of NIST have now exceeded the conventional capability to measure the shape of the Earth. Researchers explained that comparisons of atomic clocks which are located far apart could resolve geodetic measurements within 1 centimeter. Contrary to that, current measurements are in the range of several centimeters. The significance of this discovery increases many times because the comparison of two clocks is the traditional way of evaluating performance.

The Ytterbium atom falls in the list of potential candidates for redefining the international unit of time, second. Currently, Cesium atom is used but these atomic clocks at NIST meet a major requirement of the international redefinition roadmap to change a current standard. They show a 100-fold improvement in validated accuracy over the best clocks in the world. The inclusion of thermal and electric shielding, in these latest clocks, might have played a role in that as the atoms stay protected from stray fields and enable better characterization for frequency shifts.

The Einstein’s Theory of Relativity proposes that the ticking of an atomic clock is reduced (redshift) when it is being operated in an environment with stronger gravity. This means that time passes at a slower rate when we move to lower elevations. The fact that these redshifts degrade the timekeeping of an atomic clock can be manipulated, positively, to measure the gravity.

Therefore, super-sensitive atomic clocks can detect the gravitational distortion of space-time more precisely than ever. Consequently, applications like Relativistic Geodesy can detect signals from the early universe. What makes it even more interesting is that we could possibly hear the dark matter in the near future.

Nowadays, NIST is trying to develop a portable atomic clock with state-of-the-art performance. This clock will then be transported to other labs of the world for clock comparisons. Similarly, scientists will try to look for new relativistic geodesy techniques by sending it to various locations.