Using a special type of atom could make even the most advanced atomic clocks more accurate, scientists think.
If confirmed, this breakthrough, which could lead to more accurate GPS systems and better atomic clocks for space use, could even lead to devices that can detect earthquakes and volcanic eruptions with a higher level of accuracy. And fascinatingly, one of the researchers behind the development has a household name, based on a fitting family legacy rooted in the cutting edge of atomic science: Eliot Bohr. He is the great-grandson of Neils Bohr.
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Of all the units used by humanity for measurement, the second, a fundamental unit of time, is the most precisely defined. Crucial to this and to all types of time measurements throughout history are different types of oscillations. Just as grandfather clocks use the oscillations of a pendulum 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 oscillations of strontium atoms instead of cesium to measure time; the most accurate of these is accurate to 1/15,000,000,000 of a second. This means that even if the clock had run some 13.8 billion years since the beginning of time, it still wouldn't have lost or gained a full second. Yet for the majority of atomic clocks, which are used to keep Universal Coordinated Time (UTC) of positions around the world and ensure that our cell phones, computers and GPS technology are synchronized, there is still some 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 from the system. This may cause some discrepancy, even if it is incredibly small. Still, researchers at the Niels Bohr Institute believe they have found a way to eliminate the laser altogether, avoiding atomic heating and possible degradation of precision. It is an institute named after Eliot Bohr's great-grandfather, and to which Bohr himself is a member.
"We discovered that it is possible to read out the collective state of an atomic ensemble, as required in atomic clocks and sensors, at a higher speed and with minimal heating using super radiation," said lead researcher Eliot Bohr, who received his PhD. . fellow at the institute, Space.com told me. "There is a threshold for superradiation to occur for our chosen experimental geometry, and we can use this threshold in a clock sequence."
Atomic clocks could be cooler
In today's atomic clocks, about 300 million hot strontium atoms are spat into a magneto-optical trap located in a vacuum chamber. This trap is a ball of atoms that has cooled to temperatures near absolute zero, the theoretical temperature at which all atomic motion would cease. These temperatures make the introduced atoms virtually stationary. This allows two mirrors with light between them to register their vibrations.
"In traditional atomic clocks, the detection heats the atoms, requiring atoms to be recharged," Bohr said. "This loading takes a while and causes downtime in the atomic clock cycle, limiting precision."
However, the team's species of 'paused' atoms, which have cooled down so dramatically, can be reused. This means they don't need to be replaced as often, leading to more accurate atomic clocks.
Bohr explained that super-radiant atoms are atoms that exist in a collective quantum state and are excited by the addition of energy in the form of photons or light particles. When the atoms release the photon-induced energy, or "decay," they all emit light in the same direction and at an increased speed.
"You cannot fundamentally distinguish which atom emitted which photon. They emitted them together," he added. "This improved emission rate allows photons to be emitted much faster through the types of atomic transitions used in atomic clocks."
This powerful light signal can be used to read the atomic state of the collective strontium atoms, eliminating the need for a laser in the first place. And because this process occurs without heating the superradiant atoms more than a very minimal amount, they do not need to be replaced.
Abolishing the laser would not only yield more precise atomic clocks, but it could also result in devices that are simpler and more portable.
"The most modern atomic clocks are now so accurate that they are sensitive to gravity," Bohr said. "There are proposals that if we have atomic clocks that are portable and accurate enough, we can place them strategically and better predict earthquakes and volcanic eruptions by measuring certain variations in gravity."
Revolutionary atomic science is the family business
Coming from a line of scientists who have been influential in our understanding of the subatomic world, Bohr may have this kind of research in his blood. The most famous in this line is his great-grandfather, Niels Bohr, one of the founders of quantum physics and a scientist who made enormous contributions to the understanding of atomic structure, without whom such research could not take place.
In 1913, Niels Bohr, together with Ernest Rutherford, presented a model of the atom, suggesting that it was a dense nucleus surrounded by orbiting electrons. 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 students to the concept of the atom in classrooms around the world.
Eliot Bohr's family's connection to atomic structure also goes deeper than this.
His grandfather is Aage Niels Bohr, who received the Nobel Prize in Physics in 1975 together with Ben Roy Mottelson and James Rainwater for their discovery of the connection between collective motion and particle motion in atomic nuclei. This led to the development of an improved theory of the structure of the atomic nucleus.
"Both my great-grandfather and my grandfather inspired me tremendously," Bohr said. 'They both worked on theoretical work, gaining insight into the atom and the nucleus. My great-grandfather's theory that atoms can absorb a photon of a certain wavelength and go to an excited state, or emit a photon and decay to a lower state, is exactly what we do every day in our laboratory using lasers."
Bohr added that it is the openness of his great-grandfather and colleagues that he finds particularly inspiring.
"The concepts are completely non-intuitive, but through rigorous data and debate, they accepted these new 'quantum' rules," Bohr said. "We now accept them and use them in many of our modern technologies. I hope to contribute to the development of the next quantum technologies that will benefit society."
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As for his superradient atomic clock research, Bohr said there are many opportunities for future progress. The group he was part of in Copenhagen now continues to understand various properties of superradiant light to see how it can be used for other situations.
Meanwhile, Bohr has started a postdoctoral research position at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado, Boulder. This is a laboratory that also studies super radiation 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 concluded. "We have some ideas to further refine the method, such as finding the optimal parameters and understanding and reducing the noise level in the superradiant signal.
"There are many opportunities to use super radiation to advance clocks and sensor technology."
The team's research was published in February in the journal Nature Communications.
