A new, more accurate atomic clock could help detect dark matter and study the effect of gravity on time

The atoms are trapped in an optical cavity made of two mirrors. When a “piezo” laser is set through the cavity, the atoms are entangled and their frequency measured with a second laser, as a platform for more accurate atomic clocks. Credit: with permission from researchers

The new atomic clock design, which uses entangled atoms, could help scientists discover dark matter and study the effect of gravity on time.

Atomic clocks are the most accurate timers in the world. These remarkable instruments use lasers to measure the vibrations of atoms, which oscillate at a fixed frequency, like many microscopic pendulums oscillating simultaneously. The best atomic clocks in the world keep time with such accuracy. If they have been operating since the beginning of the universe, they will only stop by about half a second today.

However, it can be more accurate. If atomic clocks can measure atomic vibrations more precisely, they will be sensitive enough to detect phenomena such as dark matter and Gravitational waves. With better atomic clocks, scientists can also begin to answer some mind-boggling questions, such as the effect of gravity on the passage of time and whether time itself changes as the universe progresses.

Now a new type of atomic clock that he designed With Physicists may enable scientists to explore such questions and perhaps uncover new physics.

Researchers report today in the journal nature They built an atomic clock that doesn’t measure a cloud of randomly oscillating atoms, as the latest designs now measure, but instead atoms that were quantitatively entangled. Atoms are bound in an impossible way according to the laws of classical physics, and this allows scientists to measure the vibrations of atoms more precisely.

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The new setting can achieve the same accuracy four times faster than hours without interlocking.

“Enhanced entanglement optical atomic clocks will have the ability to achieve better accuracy in one second than the latest current optical clocks,” says lead author Edwin Pedrozo-Peñafiel, a postdoctoral researcher in the Massachusetts Institute of Technology’s Electronics Research Laboratory.

If the latest atomic clocks were adapted to measure entangled atoms the way the MIT team was working, their timing would improve so that over the entire life of the universe, clocks would be less than 100 milliseconds.

Other co-authors of the paper from MIT are Simon Colombo, Chi Shu, Albert Adiatulin, Ziyang Li, Enrique Mendes, Boris Braverman, Akio Kawasaki, Saisuke Akamatsu, Yanhong Xiao, and Vladan Volitik, professor of physics at Lester Wolf.

Time limit

Since humans began tracking the passage of time, they have done so using periodic phenomena, such as the movement of the sun across the sky. Today, vibrations in atoms are the most stable periodic events that scientists can observe. Moreover, one cesium corn It will oscillate at exactly the same frequency as another cesium atom.

And to maintain the perfect time, it is better if watches follow the vibrations of one atom. But at this scale, an atom is so small that it behaves according to the vague rules of quantum mechanics: when measured, it behaves like an inverted currency that gives correct probabilities only when averaging over several fluctuations. This limitation is what physicists refer to as standard quantum limits.

“When you increase the number of atoms, the average given by all of these atoms is moving toward something that gives the correct value,” Colombo says.

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This is why atomic clocks today are designed to measure a gas made up of thousands of the same types of atoms, in order to obtain an estimate of their average oscillations. A typical atomic clock does this by first using a laser system to trap gas from supercooled atoms in a trap formed by the laser. A highly stable second laser, at a frequency close to that of the vibrations of the atoms, is sent to probe the atomic oscillation, thus tracking time.

However, the standard quantum limit is still in operation, which means that there is still some uncertainty, even among thousands of atoms, regarding their precise individual frequencies. This is where Vultek and his group showed that quantum entanglement might help. In general, quantum entanglement describes a non-classical physical condition, in which the atoms in a set exhibit correlated measurement results, even though each individual atom behaves like a random lottery of a coin.

The team concluded that if the atoms were entangled, their individual oscillations would be narrowed around a common frequency, with less deflection than if they were not entangled. Consequently, the average oscillations that an atomic clock can measure will have an accuracy beyond the standard quantum limit.

Interlocking watches

In their new atomic clock, Vultek and his colleagues entangled about 350 ytterbium atoms, which oscillate at the same very high frequency of visible light, meaning that any atom vibrates 100,000 times more in one second than cesium. If the vibrations of ytterbium could be accurately tracked, scientists could use atoms to distinguish between ever smaller time periods.

The group used standard techniques to cool the atoms and lock them in an optical cavity made of two mirrors. Then they send a laser through the optical cavity, where it moves between the two mirrors, interacting with atoms thousands of times.

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“It looks like light is a connection between atoms,” explains Shaw. “The first atom that sees this light will modify the light a little, and this light also modifies the second atom, and the third atom, and through many rotations, the atoms know each other together and start to behave similarly.”

In this way, researchers quantitatively interlock the atoms, then use another laser, similar to existing atomic clocks, to measure their average frequency. When the team conducted a similar experiment without entangling the atoms, they found that the atomic clock with the entangled atoms reached the required accuracy four times faster.

“You can always make the watch more accurate by measuring for a longer time,” says Voltek. “The question is, how long do you need to reach a certain precision. Many phenomena need to be measured on rapid time scales.”

He says that if today’s latest atomic clocks could be adapted to quantitatively measure entangled atoms, not only would they preserve a better time, but they could also help decipher signals in the universe such as dark matter and gravitational waves, and begin to answer some of the old questions.

“As the universe ages, does the speed of light change? Does the charge of the electron change?” Says Vultek. “This is what you can check with the most accurate atomic clocks.”

The reference: “Interlocking in the transmission of an optical atomic clock” by Edwin Pedroso Penafiel, Simon Colombo, Chi Xu, and Albert F. December 16, 2020 nature.
DOI: 10.1038 / s41586-020-3006-1

This research was supported, in part, by DarpaAnd the National Science Foundation and the Office of Marine Research.

Phil Schwartz

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