Fermions cooled to a temperature 3 billion times lower than in space for a quantum experiment

Fermions cooled to less than a billionth of a degree above absolute zero. The record has been broken. But not just for the glory. The researchers came down to such extreme temperatures to gain insight into the influence of quantum mechanics on the properties of materials.

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Those physicists falls under the category let’s close, these are quite classical particles. At least you know some of them. The electron or neutrino are fermions. That atoms ofytterbium (Yb) in the state solid can also be treated as fermions. And using beams lasersof Kyoto University researchers (Japan) has just succeeded in cooling some to an incredibly low temperature. In the order of a billionth of degree only over absolutely zero. It is about 3 billion times colder than in interstellar space. A record!

But it is not just to break a record that physicists wanted to go so low in temperature. It is that at this stage new phenomena appear. Especially quantum properties. And reaching such extreme temperatures allows them to observe systems in action that even most powerful supercomputers current is unable to simulate.

For example, there is the system that scientists call the Hubbard model. From the name of the physicist who imagined it in the early 1960s. It describes the behavior of fermions on a lattice – atoms that form, for example, a solid – which only interact when they are in the same place – the same atom. Scientists today use it to study the magnetic behavior and super leader materials. What happens when electrons behave collectively. A bit like football fans throwing an “ola” in a stadium.

Unravel the secrets of materials

Researchers at Kyoto University were interested in a rather special Hubbard model, the model called SU(N). Funny name. As long as it is not known that “SU” is a mathematical way of describing the very high symmetry of the system and that “N” denotes spin states possible for the particles that make it up. In the present experiment, ytterbium atoms, therefore. These can present six states of spin various. And for the first time, physicists have revealed magnetic correlations in a Hubbard SU(6) model. Understand that the quantum magnetic alignment of one atom affects that of others.

They hope to finally understand why solid materials come to be metalsinsulators, magnets or superconductors. Since the symmetry of the system could play a role, experiments of the type developed in Kyoto could provide answers. And why not, guide researchers towards a way to develop materials with the desired properties.

Physicists point out that the observed correlations are short-range. But upon further cooling fabricthey expect to see more subtly and more exotic. Phases that would not be ordered according to an obvious pattern. Not entirely by chance either. Phases that only appear when one can observe the system as a whole. On about 300,000 atoms in a 3D lattice. So did researchers at Kyoto University. All they have to do now is develop tools capable of measuring such behavior. The challenge has been met.

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