Physicists at MIT use basic atomic properties to make matter invisible – archyde

How ultra-dense and ultra-cold atoms become invisible

A new study confirms that when atoms are extremely cooled and compressed, their ability to scatter light is suppressed.



An atom is the smallest component of an element. It consists of protons and neutrons in the nucleus and electrons orbiting the nucleus.

“> Corn electrons are arranged in energy shells. Like concert goers in an arena, each electron occupies a seat and cannot descend to a lower level when all the seats are occupied. This fundamental property of atomic physics is known as the Pauli Exclusion Principle and explains the structure of the atomic shell, the diversity of the periodic table of the elements and the stability of the physical universe.

at the moment,


MIT is an acronym for the Massachusetts Institute of Technology. It is a prestigious private research university in Cambridge, Massachusetts founded in 1861. It is divided into five faculties: architecture and planning; Mechanical engineering; Humanities, arts and social sciences; Administration; and science. MIT’s influence includes many scientific breakthroughs and technological advances.

“> With physicists, the Pauli Exclusion Principle or the Pauli Exclusion have been viewed in a completely new way: They discovered that its effect can block the light scattering of atomic clouds.

When a photon of light penetrates a cloud of atoms, the photon and atom can usually spread like a billiard ball and scatter the light in all directions to emit light, making the cloud visible. However, the MIT team found that when atoms are cooled and highly compressed, the Pauli effect occurs and the particles have less space to scatter light. Instead, photons flow through it without being scattered.

The Pauli exclusion principle can be illustrated using the analogy of the seats on the square. Each person represents an atom while each chair represents a quantum state. At a higher temperature (a) the atoms sit randomly so that each particle can scatter light. At the lower temperature (b) the atoms agglomerate. Only those who have more space near the edges can scatter light. Credit: Courtesy of the researchers

Physicists have observed this effect in their experiments in clouds of lithium atoms. As they get cooler and denser, the atoms scatter less light and gradually become more opaque. The researchers believe that if they can push the conditions further, to temperatures of up to

Absolute zero

Absolute zero is the theoretically lowest temperature on the thermodynamic temperature scale. At this temperature all atoms of an object are at rest and the object does not emit or absorb any energy. The internationally agreed value for this temperature is -273.15 ° C (-459.67 ° F; 0.00 K).

“> Absolute zero, the cloud becomes completely invisible.

Team results reported today on science, was the first observation of the Pauli blocking effect on light scattering from atoms. This effect was predicted 30 years ago but has not yet been observed.

Wolfgang Ketterle, physics professor at John D. “What we observed is a very special and simple form of Pauli blocking, which blocks atoms from what all atoms naturally do: the scattering of light. This is the first clear observation of the existence of this effect and shows a new phenomenon in physics. “

Ketterle’s co-authors are first author and former MIT postdoc Yair Margalit, PhD student Yu-kun Lu, and Furkan Top PhD ’20. The team came from MIT’s Department of Physics, MIT’s Harvard Ultracold Atomic Center, and MIT’s Research Electronics Laboratory (RLE).

slight kick

When Ketterle came to MIT as a postdoc 30 years ago, his mentor David Pritchard, Cecil, and Ida Green, physics professor Ida Green, predicted that Pauli Blocking would dampen the way certain atoms, called fermions, scatter light.

The idea in general is that when an atom is almost completely frozen and compressed into a sufficiently narrow space, the atom will behave like an electron in an energetic shell without changing space, speed or position. If light photons flow, they cannot scatter.

Yu Kun LoYu Kun Lo

Yu-Kun Lu, a PhD student, set up optics to observe the scattering of light from extremely cold atomic clouds. Credit: Courtesy of the researchers

“An atom can only scatter photons if it can absorb the force of its impact by moving to another chair,” says Ketterle, explaining the analogy to sitting in a ring. “If all the other seats were occupied, they would not have the ability to absorb kicks and scatter photons. Therefore atoms become transparent. “

“This phenomenon has never been observed because humans could not form sufficiently cold and dense clouds,” continues Ketterle.

“Rule the Atomic World”

In recent years, physicists from the Ketterle group have developed laser-based magnetic techniques to lower atoms to extremely cold temperatures. He said the limiting factor was density.

“If the density isn’t high enough, atoms can still scatter light by jumping over a couple of chairs until they can fit,” says Ketterle. “That is the obstacle.”

In their new study, he and his colleagues used a previously developed technique to first freeze fermion clouds – in this case a special isotope of the lithium atom, which consists of three electrons, three protons and three neutrons. They froze clouds of lithium atoms to 20 microkelvin, which is about 1/10000 the temperature of interstellar space.

“We then used a highly focused laser to compress the ultra-cold atoms to record a density of about a quadrillion atoms per cubic centimeter,” explains Lu.

The researchers then aimed another laser beam at the cloud and carefully calibrated it so that the photons did not heat up the very cold atoms or change their intensity as the light penetrated them. Eventually, they used lenses and cameras to capture and count the scattered photons.

“We actually counted a few hundred photons, which is really amazing,” said Margalit. “A photon is a small amount of light, but our device is so sensitive that we can see it as a tiny point of light on the camera.”

At lower temperatures and higher intensities, atoms scatter less light, as predicted by Pritchard’s theory. At the coldest temperature, around 20 microkelvins, the atoms are 38 percent weaker, meaning that they scatter 38 percent less light than the cooler, less intense atoms.

“This very cold and very dense cloud system has another effect that can fool us,” said Margalit. “That’s why we spent several months sifting through and ruling out these effects in order to get the clearest possible measurement.”

Now that the team has determined that Pauli Blocking can actually affect an atom’s ability to scatter light, this basic knowledge could be used, according to Ketterle, to develop materials with suppressed light scattering, for example to store data in quantum computers.

“When we control the quantum world, like in a quantum computer, light scattering becomes a problem, and that means information is leaking out of your quantum computer,” he said. “This is one way of suppressing the scattering of light, and we contribute to the general idea of ​​controlling the atomic world.”

Source: “Pauli blocks light scattering in degenerating fermions” by Yair Margalit, Yu-Kun Lo and Furkan Shagri-Top and Wolfgang Ketterle, November 18, 2021 Available here. science.
DOI: 10.1126 / science.abi6153

The research was funded in part by the National Science Foundation and the Department of Defense. Related work by a team from the University of Colorado and the University of Otago appears in the same issue of science.

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