The project’s aim is to solve one of quantum computers’ primary issues – qubit corruption – by the use of transparent gas.

The Massachusetts Institute of Technology’s scientists have developed a transparent gas that can be used to produce invisible stuff. They are attempting to overcome the challenge of quantum supercomputers in this manner.

For almost 30 years, physicists have been working on this topic. They cooled the gas to an extremely low temperature, compressed it using a laser, and transformed it into a translucent material. As a result, it ceased reflecting and scattering a portion of the light that fell on it.

“What we’ve observed is one very special and simple form of Pauli blocking, which is that it prevents an atom from what all atoms would naturally do: scatter light,” said the authors, in a statement. “This is the first clear observation that this effect exists, and it shows a new phenomenon in physics.” 

The novel technology could be utilized to build light-suppressive materials for quantum computers to prevent information loss.

Pauli blocking derives from the Pauli exclusion principle, which was initially proposed in 1925 by the eminent Austrian physicist Wolfgang Pauli. Pauli postulated that all fermion particles — such as protons, neutrons, and electrons — that share the same quantum state cannot coexist in the same space.

Because there are a finite amount of energy states at the eerie quantum level, this drives electrons in atoms to stack into shells of higher energy levels that orbit progressively farther away from atomic nuclei. Additionally, it keeps the electrons of distinct atoms apart because, as noted in a 1967 paper co-authored by renowned scientist Freeman Dyson, without the exclusion principle, all atoms would collapse together and explode in a massive burst of energy.

These outcomes not only result in the striking variety of the periodic table’s elements, but also prevent our feet from falling through the earth and colliding with the Earth’s core.

The exclusion principle also holds true for atoms in a gas. Generally, atoms in a gas cloud have a lot of space to bounce around in, which means that even though they are fermions bound by the Pauli exclusion principle, they have enough vacant energy levels to jump into that the principle does not greatly hamper their mobility. Send a photon, or light particle, into a relatively heated gas cloud, and each atom it collides with will interact with it, absorbing the photon’s incoming momentum, recoiling to a new energy level, and scattering the photon away.

However, as a gas is cooled, the scenario changes. Now the atoms are losing energy, filling all of the lowest possible states and generating what is known as a Fermi sea. The particles are now caged in by one another, unable to migrate to higher or lower energy levels.

At this point, the researchers noted, they are stacked in shells similar to seated concertgoers in a sold-out arena and have nowhere to flee if struck. They are so densely packed that the particles lose their ability to interact with light. The light that is transmitted is Pauli-blocked and will simply pass through.

“An atom can only scatter a photon if it can absorb the force of its kick, by moving to another chair,”  Ketterle said. “If all other chairs are occupied, it no longer has the ability to absorb the kick and scatter the photon. So, the atom becomes transparent.”

However, achieving this state for an atomic cloud is extremely challenging. It demands not only extremely low temperatures, but also the atoms to be crushed to unprecedented densities. It was a delicate procedure, so the researchers blasted their gas with a laser after capturing it inside an atomic trap.

In this scenario, the researchers adjusted the laser photons so that they collided exclusively with atoms travelling in the other direction, slowing and therefore cooling the atoms. The researchers chilled their lithium cloud to a temperature of 20 microkelvins, barely above absolute zero. The atoms were then squeezed to a record density of around 1 quadrillion (1 followed by 15 zeros) atoms per cubic centimeter using a second, narrowly focused laser.

Then, to determine how well-hidden their supercooled atoms had become, the researchers used a third and final laser beam — precisely adjusted to avoid altering the gas’s temperature or density — to shine at their atoms, counting the scattered photons with a sensitivity camera. As predicted by their theory, their chilled and squeezed atoms dispersed 38% less light than those at normal temperature, effectively dimming them.

Two other independent teams demonstrated the phenomenon by cooling two additional gases, potassium and strontium. In the strontium experiment, Pauli’s team blocked excited atoms to keep them in an excited state for an extended period of time. Each of the three publications demonstrating Pauli blocking was published in the journal Science on Nov. 18.

Now that researchers have demonstrated the Pauli blocking effect for the first time, they may potentially use it to make light-blocking materials. This would be particularly beneficial for increasing the efficiency of quantum computers, which are now limited by quantum decoherence – the loss of quantum information (delivered by light) to the environment of the computer.

“Whenever we control the quantum world, like in quantum computers, light scattering is a problem and means that information is leaking out of your quantum computer,” said the authors.

“This is one way to suppress light scattering, and we are contributing to the general theme of controlling the atomic world.”

Source: 10.1126/science.abi6153

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