Researchers have developed a new approach in optical atomic clocks that brings forth a major goal in science: the redefinition of a second. The fundamental unit of time could soon be based on something beyond the transition of two hyperfine ground states of cesium, which has been the definition since 1967. The first concrete step in changing it has now happened.
Over the last several years, researchers have shown that it is possible to design clocks 1,000 times more precise than the atomic clocks that the original definition of the second is based on. These optical atomic clocks have broken record after record, but an important challenge for the redefinition was comparing the different clocks with high enough precision.
This process is difficult but it is also laborious. Measuring the frequency ratios – the comparison between different clocks – often takes many days. The new multi-ion design is scalable and its scalability is set to make the comparison short. If you have 10 ions in the clock, the measurement is 10 times faster.
This is already an important development, but the team was able to do more. To demonstrate that the clocks are good enough to lead to the redefinition of the second, the target to beat was a frequency ratio of less than 5×10-18 or less than five parts per billion billion. The team was able to achieve just that.
The system still has a lot more potential.
Dr Jonas Keller
“Here we measure the frequency ratio of a single ion clock, which is an older established clock that has been running for more than 10 years now – a ‘classical clock’. And we compared our clock to that clock. So the error contributions of Clock one and Clock two go into this combined error budget because that was really about measuring frequency ratios, which is one of the benchmarks for a [possible] redefinition of the second,” Professor Tanja Mehlstäubler told IFLScience.
“The benchmark said only if there are several people who can measure it below 5×10-18 then we can go a step towards the redefinition. That’s why it was very important for us to cross this benchmark. In that sense there we really broke a true world record because nobody so far compared two types of optical clocks at that level!”
The record-breaking achievement is extremely exciting. It is something to be happy about, but it is also very much a beginning. Theoretical work has suggested that this multi-ion clock has the ability to go even further in reducing uncertainty.
“We’ve been showing in 2019 what these systems can theoretically do. This was the first actual demonstration of clock operation with such uncertainty. The system still has a lot more potential. It can go down to 1×10-19 in systematic uncertainty as we’ve shown in principle. But of course, the challenge is actually to do it,” Dr Jonas Keller, one of the first authors of the work, told IFLScience.
It’s very rewarding to work in a field where very precise measurements are possible because the more precise you measure the more surprises you’re up to get.
Professor Tanja Mehlstäubler
Improving the definition of the second is clearly a major focus of this work but the development of these clocks has some incredible applications. These clocks are sensitive to tiny gravitational effects. The same clock could tell if they have been moved up and down by a few millimeters. So they can be used to track the motion of the Earth, and the changes in elevation of land masses due to glaciers disappearing or melting permafrost.
These clocks can help further probe the limits of our physics both in general relativity and quantum mechanics. They sit at the cutting edge of our knowledge of the fundamental universe. But they are not science fiction. They are very much real.
“It’s very rewarding to work in a field where very precise measurements are possible because the more precise you measure the more surprises you’re up to get. I’m really looking forward to measuring time so precisely,” Professor Mehlstäubler told IFLScience.
A paper describing the achievement is published in the journal Physical Review Letters.
Source Link: Multi-Ion Optical Atomic Clock Takes A Step Towards Changing The Definition Of A Second
