by Using a special type of atom could make even the most advanced atomic clocks more accurate, according to scientists.
If confirmed, the breakthrough could lead to more accurate GPS systems and better atomic clocks for use in space travel – even devices that could detect earthquakes and volcanic eruptions with a higher level of accuracy. And very interestingly, one of the researchers behind the development has a well-known name, based on a family legacy of adaptation rooted in the pioneering of atomic science: Eliot Bohr. He is Neils Bohr’s grandson.
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Of all the units used by mankind for measurement, the second most defined is the fundamental unit of time. Various types of oscillations are crucial to this and all types of time measurement throughout history. Just as grandfather clocks use pendulum oscillations to measure time, atomic clocks define a second as 9,192,631,770 microwave oscillations of a cesium atom as it absorbs microwave radiation of a specific frequency.
Many modern atomic clocks use the oscillations of strontium rather than cesium atoms to measure time; the most accurate of these is accurate to within 1/15,000,000,000 of a second. This means that even if it had been running since the beginning of time around 13.8 billion years ago, the clock would still not have lost or gained a full second. However, for most atomic clocks, which are used to keep Coordinated Universal Time (UTC) from positions around the world and ensure that our mobile phones, computers and GPS technology are in sync, there is still room for improvement.
That’s because the laser used to read the oscillations of atoms in atomic clocks heats up those atoms in the process, causing them to escape the system. This can create some inconsistency, although that change is small. Still, researchers from the Niels Bohr Institute think they have found a way to eliminate the laser altogether, thereby avoiding atomic heating and possible precision degradation. It is an institution named for Eliot Bohr’s great-grandfather, and one Bohr himself is affiliated with.
“We found that it is possible to read out the collective state of an atomic ensemble, as needed in atomic clocks and sensors, at an enhanced rate and with minimal heating using superradiance,” lead researcher Eliot Bohr, who was in his Ph.D. . member at the institute, said Space.com. “There is a threshold for superradiance for our chosen experimental geometry, and we can leverage this threshold in a clock sequence.”
Atomic clocks could be cooler
In current atomic clocks, about 300 million or so hot strontium atoms are spaced into a magneto-optical trap located inside a vacuum chamber. This trap is a ball of atoms cooled to a temperature close to absolute zero, the theoretical temperature at which all atomic motion would stop. Because of these temperatures, the introduced atoms lie almost still. So two mirrors with light between them can register their oscillations.
“In traditional atomic clocks, the detector heats up the atoms, which requires atoms to be freshly charged,” said Bohr. “This loading takes time and causes downtime in the atomic clock cycle, limiting accuracy.”
The type of team’s “rest” atoms that have cooled so much, however, can be reused. This meant that they would not need to be replaced as often, and therefore led to more accurate atomic clocks.
Bohr explained that superradiant atoms are atoms that exist in a collective quantum state and are excited to add energy in the form of photons, or particles of light. When the atoms release the photon-induced energy, or “decay,” they all emit light in the same direction and at an enhanced rate.
“There is no fundamental distinction to be made between which atom emits the photon. They emitted them together, together,” he said. “This enhanced emission rate allows much faster emission of photons from the types of atomic transitions used in atomic clocks.”
This powerful light signal can be used to read out the atomic states of common strontium atoms, meaning that a laser is not needed in the first place. And, again, because this process takes place without heating the superradiant atoms more than a very small amount, replacement will not be necessary.
The success of the laser would not only lead to more accurate atomic clocks, but could lead to simpler and more portable devices.
“State-of-the-art atomic clocks are now so precise that they are sensitive to gravity,” Bohr said. “There are suggestions that if we have atomic clocks that are portable and precise enough, we can strategically place them and better predict earthquakes and volcanic eruptions by measuring certain variations in gravity.”
Revolutionary atomic science is the family trade
Coming from a line of scientists who have influenced our understanding of the subatomic world, this type of research may well be in Bohr’s blood. His great-grandfather, Niels Bohr, is one of the fathers of quantum physics and a scientist who greatly contributed to the understanding of the atomic structure, without which research like this could not have happened.
In 1913, Niels Bohr, together with Ernest Rutherford, presented a model of the atom, suggesting that it is a dense nucleus with electrons orbiting around it. Although this “Bohr model” of the atom is now considered relatively simplistic compared to the detailed diagrams we have today, 111 years after its creation, it is still used to introduce the concept of the atom to students in classrooms on around the globe.
Eliot Bohr’s family’s connection to atomic structure also goes deeper than this.
His grandfather is Aage Niels Bohr, who was awarded the Nobel Prize in Physics in 1975 along with Ben Roy Mottelson and James Rainwater for their discovery of the connection between collective motion and the motion of particles in atomic nuclei. This led to the development of an improved theory of the structure of the atomic nucleus.
“My great-grandfather and grandfather really inspired me,” Bohr said. “They both worked on theoretical work, understanding the atom and the nucleus. My great-grandfather’s theory is that atoms can absorb a photon of a certain wavelength and go to an excited state, or emit a photon and decay to lower state, which is exactly what we do in our lab every day using lasers.”
Bohr added that he is particularly inspired by the open-mindedness shown by his great-grandfather and his peers.
“The concepts are completely non-intuitive, but through data and intense discussions, they accepted these new ‘quantum’ rules,” said Bohr. “We now accept them and use them in many of our modern technologies. I hope to contribute to the development of other quantum technologies that will benefit society.”
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Regarding his atomic clock superradiant research, Bohr said that there are many possibilities for the future. The group he was a part of in Copenhagen is now continuing to understand the various properties of super-radiant light to see how it can be used in other situations.
Meanwhile, Bohr has started a postdoctoral research position at JILA, a joint institute between the National Institute of Standards and Technology (NIST) and the University of Colorado, Boulder. This is a laboratory that also studies superradiance and other collective atomic effects for next-generation quantum sensors.
“I plan to continue researching collective quantum effects that can be used in clocks and sensors,” he said. “We have some ideas for further refining the method, such as finding and understanding the best parameters and reducing the noise level in the superradiant signal.
“There are many possibilities for using superradiance to advance clocks and sensor technology.”
The team’s research was published in February in the journal Nature Communications.
