The quantum effect predicted thirty years ago is finally observed

In three different experiments, physicists saw the development of a Pauli blockade: a quantum phenomenon in which a dense, cloudy quantum gas suddenly becomes transparent. This is the first time that this phenomenon has been observed.

If you cool a dense cloud of quantum gas enough, you can see through it. This phenomenon, which in English Pauli blocking mentioned, had never been seen before.

“This was theoretically predicted over three decades ago,” said physicist Amita Deb of the University of Otago in New Zealand, a member of one of three teams that observed the phenomenon. “This has now been proven experimentally for the first time. “

Excluded

Pauli blocking occurs in particles called fermions. This class of particles includes the protons, neutrons, and electrons that make up all matter. Fermions follows a rule that the Pauli exclusion principle hot. This prescribes that two identical fermions can never have the same quantum state.

“That same principle is the reason you don’t fall to the ground,” says physicist Brian DeMarco of the University of Illinois at Urbana-Champaign, who was not involved in the experiments. “The underlying physics is very difficult to observe, but the effect is all around you and determines the structure and stability of matter.”

Pauli blocking occurs when the fermions of a gas are so dense that all available quantum states are filled. When this is the case, the particles can no longer move.

Mandatory immobilization

Usually, the light falling on the gas would be absorbed or reflected by the particles. In addition, the light inevitably gives some movement to the particles. This is not an option for particles which should in principle remain stationary. The light will therefore neither be absorbed nor reflected by these particles. Instead, it’s forced to shine through, without any interaction with the gas.

“It’s a very basic phenomenon, but it’s devilishly hard to see,” said Yair Margalit of MIT, a member of one of the three teams. “It takes extreme conditions to make it visible – high densities and ultra low temperatures – and it’s hard to achieve both at the same time. “

Close and cold

All three groups played similar experiences of, with atoms that were in “magnetic traps” where magnetic fields hold the particles in place. These atoms have been cooled to near absolute zero. Each team used a different atom, but found similar results: the light scattering of gases was significantly weaker when they were cold and dense enough to cause a Pauli blockade.

“It’s great that three experiments were done at the same time and look at the problem from different angles,” Deb says. The results of the three were in agreement.

Pinned particle

The discovery could help researchers study atoms in so-called high-energy excited states. Such a condition tends to worsen quickly. “Imagine taking an excited atom from somewhere else and placing it in such gas with a Fermi blockade. When he tries to get out of the excited state, he has nowhere to go. The lifespan of this disease is therefore artificially prolonged, ”said Christian Sanner of the JILA Research Institute in Colorado, a member of one of the teams.

The phenomenon could also be useful in quantum computers, according to the researchers. The atoms used in some of these devices are extremely sensitive to incident light. By carrying out a Fermi blockade in certain parts of the computers, this sensitivity would decrease and they would be able to maintain their quantum state for longer. This can benefit the stability of quantum computers.