Wolfgang Ketterle, a physics professor at the Massachusetts Institute of Technology (MIT) in the US, realized ‘Bose-Einstein aggregation’ at near absolute temperature and succeeded in creating a new state of matter in which numerous atoms are united as one, Cornell, Y. Together with Mun, he was awarded the 2001 Nobel Prize in Physics.
However, when he first came to MIT as a postdoctoral researcher in 1990, his advisor, Professor David Pritchard, predicted a quantum effect called ‘Pauli blocking’. It was the claim that atoms could be made transparent and invisible if they were arranged in a high density at a cryogenic temperature.
This bizarre quantum effect is named Pauli blocking because it is based on the ‘Pauli’s exclusion principle’ first formulated in 1925 by the Austrian physicist Wolfgang Pauli.
Pauli asserted that Fermi particles such as protons, neutrons, and electrons cannot exist in the same space with the same quantum state. In other words, particles like electrons have reserved seats, so two identical particles cannot sit on the same spot at the same time.
38% less light scattering than room temperature atoms
We can see some matter because light (photons) striking an atom bounces off and scatters the light’s energy. However, according to Pauli’s exclusion principle, if atoms fill the surrounding space densely, the atoms cannot move, so light scattering does not occur, and we cannot see it either.
Pauli’s exclusion principle also applies to atoms of gases. Atoms in a normal gas have a lot of space to bounce off, so even Fermi particles can scatter photons far away. But if you make the gas colder and denser, it’s a different story. At this point, the particles are closed to each other and cannot scatter the energy the photons hit, so they become transparent and invisible to our eyes.
To put it simply, think of the audience sitting in a concert hall. If there are many empty seats in the theater, the audience can vibrate to the empty seats and scatter the light, but when the seats are sold out and the audience is full, the particles can no longer interact with the light and can’t scatter photons.
However, this phenomenon has never been observed before. It was not possible to create a condition that was cold enough and dense enough for a Pauli block to occur.
However, Professor Wolfgang Keterly succeeded in proving the Pauli blocking phenomenon predicted by his teacher for the first time in 30 years.
First, the researchers used a special isotope of lithium atoms with three electrons, three protons and three neutrons to cool the atomic cloud of lithium to 20 microkelvins (μK), which is higher than absolute zero. This is about 1/100,000th the temperature of interstellar space.
Then, using a laser capable of compressing cryogenic atoms, the atoms were squeezed to a density of 1,000 trillion atoms per cubic centimeter. Finally, the researchers counted the number of scattered photons using a high-precision camera and another laser beam carefully calibrated so as not to change the temperature or density of the gas.
Useful for improving quantum computer efficiency
The results showed that the cooled and densified atoms had 38% less light scattering than the atoms at room temperature. This means that the atoms are 38% darker and that much more transparent.
A 38% reduction in light scattering does not mean that atoms are transparent. However, the researchers said if the cloud of atoms could be cooled to absolute zero (-273.15°C), the atoms would not be able to scatter light at all, making them completely invisible. The results of this study were published in the November 18th issue of the international academic journal ‘Science’.
“What we observed is a very special and simple form of Pauli blocking, which is that atoms prevent light scattering, which is what all atoms do naturally,” said Professor Wolfgang Keterley, who led the study. “This is the first time we’ve observed it, and it reveals a new phenomenon in physics.”
The study, which observes that Pauli blocking can actually affect an atom’s ability to scatter light, could be particularly useful for improving the efficiency of quantum computers.
Current quantum computers are hampered by quantum coherence, so the quantum information carried by light is lost around the computer. This research has found a way to suppress the scattering of light, which is a problem whenever the quantum world is controlled.