A team of physicists from the University of Wisconsin-Madison in the US has developed one of the most high-performance atomic clocks ever created. The invention allows scientists to test new methods for searching for gravitational waves and dark matter.
This device, known as an atomic clock on an optical lattice, is able to measure the difference in time with an accuracy equivalent to losing one second every 300 billion years. The new clock is the first real example of a “multiplexed” optical clock.
“The optical lattice watch is already the best watch in the world – we got a level of performance that no one has seen before. We are working both to improve their performance and to develop new applications that will be possible with this increased performance,” said Szymon Kolkowitz, senior author of the study, UW-Madison physics professor.
The question arises – what makes atomic clocks so accurate. When the energy levels of an electron fluctuate, they react by absorbing or emitting light of the same frequency associated with all atoms of a particular element. Optical atomic clocks accurately keep time using a laser tuned to match these frequencies. This is an incredibly complex process that requires the most advanced lasers in the world.
Scientists led by Kolkowitz have created a multiplexed clock that allows strontium atoms to be divided into several clocks arranged in a line in a single vacuum chamber. They noted that with a single atomic clock, their laser was only able to reliably excite electrons in the same number of atoms for one tenth of a second. But when the same laser was directed at two clocks in the chamber at the same time, the number of atoms with excited electrons remained the same between the two clocks for a full 26 seconds.
The researchers then wanted to see how accurately they could measure the difference between clocks. Scientists conducted their experiment more than 1000 times. As expected, the ticking of the clock was slightly different (due to two slightly different locations). As more and more measurements were recorded, the research team was able to better understand and measure these fluctuations. By the end of this process, the researchers were able to narrow down this difference in ticking between two clocks to the rate at which they drifted apart by just one second every 300 billion years. This precise measurement of accurate timekeeping sets a new world record for two spaced clocks.
This work would have set another world record for the most accurate frequency difference if not for another study published in the same issue of Nature. This project, led by JILA (a research institute in Colorado), found the frequency difference between the top and bottom of a scattered cloud of atoms about 10 times more accurate than the UW-Madison team of scientists.
The JILA team’s results at a distance of one millimeter also represent the shortest distance at which Albert Einstein’s general theory of relativity has been tested with a watch. Prof. Kolkowitz’s team wants to do similar work in the near future.
“The surprising thing is that we showed the same performance as the JILA group, despite the fact that we use a laser several orders of magnitude worse,” Professor Kolkowitz commented on the study.
To better demonstrate all possible uses for their clock, the research team compared the frequency changes between each pair of six multiplexed clocks in a cycle. This led to the discovery that the difference in sum is zero when the first clock is looped back. Observation confirms the accuracy and consistency of the measurements, opening the door to detect tiny frequency changes in this network.