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Opposing the Pauli exclusion principle; Physicists’ solution to prevent the scattering of light by atoms

Cold or supercool atoms are atoms that are stored at temperatures close to zero Kelvin (absolute zero) and usually below several tens of microclavines (μK), and this is exactly the temperature at which the mechanical properties of the quantum of atoms appear. To achieve such a low temperature, usually a combination of several techniques must be used. First, atoms are usually trapped in an optical magnetic trap by laser cooling and pre-cooled. To achieve the lowest possible temperature, further cooling is performed using an evaporative cooler in a magnetic or optical trap.

Supercooled atoms are typically produced by diluting the gas field with a laser field. In 1901, three researchers, including Leddoff, Nichols, and Holl, discovered evidence of the radiation pressure exerted by the force of light on atoms, which eventually led to the invention of the laser and the development of additional techniques for manipulating atoms with light.

The use of laser light to cool atoms was first proposed in 1975, using the Doppler effect to generate radiation power at an atom quickly; The method is known as Doppler cooling. In addition, similar ideas have been proposed for cooling trapped ion samples. The use of Doppler cooling in a three-dimensional manner reduces the velocity of the atoms at velocities typically a few centimeters per second, leading to the production of optical mortar.

Despite all this, cold atoms can be a good source of energy for the future atomic computer and bring it closer to operating conditions. It is now said that a group of physicists at MIT University have been able to solve important bottlenecks in future quantum computers by cooling atoms. To better understand, we must first explain this a little.

In general, the electrons of an atom are arranged in layers of energy and can be described to people who go to the stadium to watch a football game. Imagine that each person (electron) occupies one seat, and if the stadium occupies all of its seats, the person will not be able to access the lower seats. This basic feature 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 elements, and the stability of the material world.

Now, MIT physicists have applied the principle of Pauli exclusion or Pauli blocking in a completely new way; They found that this effect could prevent light from scattering through an atomic cloud. Typically, when photons of light penetrate a cloud of atoms, the particles can separate like billiard balls and scatter the photons in any direction to illuminate the net, making the cloud visible. However, the MIT team observed that when atoms become supercooled and supercompressed, the Pauli effect begins and the particles effectively have less space for light scattering. Instead, photons pass through them without scattering.

In their experiments, physicists observed this effect in a cloud of lithium atoms and found that as they became colder and denser, the atoms scattered less light and gradually became darker. Researchers think that if they can bring the conditions to absolute zero, the cloud will become completely invisible. The team’s results show the first observation of the Pauli blocking effect on light scattering by atoms.

It is interesting to note that this work was predicted almost three decades ago, but has remained a mystery until now. Wolfgang Cutler, The project’s lead author and professor of physics at MIT, says:

Pauli blocking has been proven in general and is absolutely necessary for the stability of the world around us. What we have observed is a very special and simple form of blocking a pulley that prevents the scattering of atomic light (which all atoms do naturally). This is the first clear observation of the existence of this effect and indicates a new phenomenon in physics.

You might know that when Cottrell came to MIT 30 years ago as a postdoctoral fellow, David Pritchard, His professor had predicted that blocking Pauli’s exclusion principle could be used to prevent light scattering by using special atoms known as fermions! In general, his idea was that if atoms were almost frozen and compressed in tight space, atoms would behave like electrons in energetic shells and have no place to change their velocity or position; Therefore, if light photons flow in, they cannot scatter and activate atoms.

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“An atom can only scatter a photon if it can absorb the force of its impact by moving to another seat,” Catherine explains, citing the analogy of a seat in a stadium. If all other seats are occupied, it will no longer be able to absorb shock and scatter photons; Thus, the atom becomes transparent. “This phenomenon has never been seen before, because scientists have not been able to create clouds with sufficient cold and density.”

In recent years, physicists, including the Cottrell group, have developed magnetic and laser-based techniques to dramatically lower the temperature of atoms; But “density” has always been a limiting factor in this process. Cottrell argues that if the density is not high enough, an atom can still scatter light by jumping from a few chairs (as in the beginning of the article) until it finds space, and this is the bottleneck that researchers have been using for years. Involved.

A new study suggests that Cattle and colleagues used techniques they had previously developed to first freeze a cloud of fermions. In this case, the special isotope of the lithium atom has three electrons, three protons and three neutrons. They froze a cloud of lithium atoms up to 20 microns, which is about 1/100000 of the temperature of interstellar space!

The team then used a centralized laser to compress supercooled atoms to record density, reaching about four billionths of an atom per cubic centimeter. The researchers also launched another laser beam into the cloud to accurately calibrate it so that its photons would not heat up the supercooled atoms or change their density as light passed through. Finally, they used a lens and a camera to capture and count the photons that managed to scatter. “The pearl says:

We actually count a few hundred photons, which is really amazing. A photon is a small amount of light; But our equipment is so sensitive that we can see it as a tiny speck of light on the camera!

The results show that at gradually colder temperatures and higher densities, atoms scatter far less light, just as Pritchard’s theory predicted 30 years ago. At its coldest, at about 20 microclavines, atoms are 38 percent less light; This means that atoms scatter 38% less light than cold, dense atoms.

“This achievement of super-cold and very dense clouds has other effects that could possibly deceive us,” says Margalit. “So we spent several months screening and putting these effects aside to get the clearest measurement.” Now proving that the Pauli exclusion principle can actually affect the atom’s ability to scatter light, Cottrell says that this basic knowledge may be used to develop light-repellent materials, for example, to preserve data in quantum computers. He adds at the end:

Whenever we control the quantum world like quantum computers, light scattering will be a problem, and it means that information is leaking from your quantum computer. This is one way of counteracting light scattering, and we are helping to address the overall issue of controlling the atomic world.


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