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

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Ce sont des atomes d’ytterbium que des chercheurs de l’université de Kyoto (Japon) sont parvenus à refroidir à une température record pour des fermions. © Negro Elkha, Adobe Stock

The fermions were cooled to less than a billionth of a degree above absolute zero. The record is broken. But not just for the glory. If researchers have gone down to such extreme temperatures, it is to learn about the influence of quantum mechanics on the properties of materials. You may also be interested.
[EN VIDÉO] Interview: Is there a maximum temperature? Since there is a minimum temperature that represents the almost absolute immobility of atoms or molecules (-273.15°C), does the impossibility of exceeding the speed of light impose a maximum temperature? As part of its Expert Questions on Physics and Astrophysics video series, the publishing house De Boeck asked José-Philippe Pérez, professor emeritus at the University of Toulouse de Languedoc, to answer this question. What physicists classify as fermions are quite classical particles. At least you know some of them. The electron or neutrino are fermions. Ytterbium (Yb) atoms in the solid state can also be treated as fermions. And, with the help of laser beams, researchers at the University of Kyoto (Japan) have just managed to cool it to an incredibly low temperature. On the order of one billionth of a degree just above absolute zero. That’s about 3 billion times colder than interstellar space. A record! But physicists didn’t just want to break such a low temperature record. It is that new phenomena appear at this stage. Quantum properties, in particular. And reaching such extreme temperatures allows them to observe systems in action that even today’s most powerful supercomputers are unable to simulate, such as the system the researchers call the Hubbard model. From the name of the physicist who imagined it in the early 60s. It describes the behavior of fermions in a network – atoms that form a solid, for example – that only interact when they are in the same place – the same atom -. Researchers today use it to study the magnetic and superconducting behavior of materials. What happens when electrons behave collectively. A bit like football fans throwing a ‘wave’ in a stadium. Discovering the secrets of materials Researchers at Kyoto University have been interested in a rather special Hubbard model, the model called SU(N). funny name While we do not know that “SU” is a mathematical way of describing the very high symmetry of the system and that “N” designates the possible spin states of the particles that make it up. In the present experiment, the ytterbium atoms, therefore. These can present six different spin states. 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. What they hope is to finally understand why solid materials become metals, insulators, magnets or superconductors. Because 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 by cooling the material even further, they expect to see more subtle and exotic phases appear. Phases that would not be ordered according to an obvious pattern. Not completely random either. Phases that only appear when the system can be observed as a whole. In about 300,000 atoms of a 3D network. Just like researchers at Kyoto University. All they have to do now is develop the tools capable of measuring this behavior. The challenge is met. Interested in what you just read?
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