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Pushing frontiers in precision time

Dutch and Indian researchers arrive at a breakthrough in the development of the optical clock.

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Did you know that the standard unit we use to measure time, the second, is currently defined as the duration of 9192631770 (9.19 billion) cycles of microwave emissions by the caesium atom? Scientists the world over are attempting to measure time with greater and greater precision. For a decade, experiments have been undertaken to measure time using the number of cycles of light waves.

A team of researchers in India and the Netherlands has now reached a step closer in arriving at greater precision in the measurement of time through this method. In place of the atomic clocks, they are experimenting with o-clocks (optical clocks).

Atomic ions with their low-lying energy levels in the optical region  of the electronic spectrum are used in operating the o-clocks.
Using a novel theoretical approach, scientists of Bangalore-based Indian Institute of Astrophysics (IIA) and the Indian Association for Cultivation of Science (IACS), Kolkata, in collaboration with the University of Groningen in the Netherlands brought o-clock experimenters closer to being able to make the most accurate watches in existence.

“An optical clock measures the number of cycles of light waves. In future, it could be used to define a second more accurately than an atomic clock. However, this is experimentally very challenging as there are a number of possible sources of errors in such a measurement,” said the co-author of the study, BP Das, a faculty member at the IIA.

The bulk of the work in the development of the o-clock was done by Bijaya Kumar Sahoo, who completed his PhD under Das’s supervision at the Indian Institute of Astrophysics. Sahoo is currently a Veni Postdoctoral Fellow at the University of Groningen in the Netherlands, and also the lead author of the study.

Das explained that the sources of error in the measurement of time in an o-clock lie in the perturbations caused by stray electric fields and electromagnetic radiation emitted by the ions. “Ions of strontium, barium and radium, which we have considered in our study, are trapped using electromagnetic force and cooled with laser beams to reduce the error in the measurements.

However, perturbations from stray electric fields or electromagnetic radiation emitted by the ions shift the energy levels of the ions, leading to deviation from the expected travel pattern of light waves,” said Das.

Das added that it took the team two years to finalise the theory that drove the experiment, and to put in place the computer programme that would support the scientific work.  The team has now published a paper on the sources and amount of error likely in the scientific calculations.

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