In a laboratory in Kyoto, Japan, researchers are working on some very interesting experiments. A team of scientists from Kyoto University and Rice University in Houston, Texas, cooled matter to within a billionth of a degree from absolute zero (the temperature at which all motion stops), making it the coldest matter in the world. whole universe. The study was published in the September issue of Physics of natureand “opens a portal to an unexplored realm of quantum magnetism,” according to Rice University.
“Unless an alien civilization is doing experiments like these right now, every time this experiment is underway at Kyoto University it produces the coldest fermions in the universe,” Rice University professor Kaden Hazzard said. corresponding theory author of the study and member of the Rice Quantum Initiative, in a press release. “Fermions are not rare particles. They include things like electrons and are one of the two types of particles that all matter is made up of ”.
The Kyoto team led by study author Yoshiro Takahashi used lasers to cool fermions (or particles such as protons, neutrons and electrons whose quantum spin number is an odd half integer like 1/2 or 3/2) of ytterbium atoms within about one-billionth of a degree of absolute zero. It is about 3 billion times colder than interstellar space. This area of space is still heated by the cosmic microwave background (CMB), or the afterglow from the Big Bang radiation … about 13.7 billion years ago. The coldest known region of space is the Boomerang Nebula, which has a temperature of one degree above absolute zero and is 3,000 light-years from Earth.
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Just like electrons and photons, atoms are subject to the laws of quantum dynamics, but their quantum behaviors only become evident when they are cooled to within a fraction of a degree of absolute zero. Lasers have been used for more than 25 years to cool atoms to study the quantum properties of ultracold atoms.
“The advantage of having this cold is that the physics really change,” Hazzard said. “Physics starts to get more quantum mechanics and allows you to see new phenomena.”
In this experiment, lasers were used to cool matter by stopping the movement of 300,000 ytterbium atoms within an optical lattice. It simulates the Hubbard model, a quantum physics first proposed by theoretical physicist John Hubbard in 1963. Physicists use Hubbard models to study the magnetic and superconducting behavior of materials, especially those in which interactions between electrons produce a collective behavior,
This model allows atoms to exhibit their unusual quantum properties, which include the collective behavior between electrons (somewhat like a group of fans running “the wave” at a football or soccer match) and superconducting. or the ability of an object to conduct electricity without losing energy.
“The thermometer they use in Kyoto is one of the important things our theory provides,” Hazzard said. “By comparing their measurements with our calculations, we can determine the temperature. The record temperature is reached thanks to a new and fun physics that has to do with the very high symmetry of the system “.
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Hubbard’s model simulated in Kyoto has a special symmetry known as SU (N). SU stands for special unitary group, which is a mathematical way of describing symmetry. The N indicates the possible spin states of the particles within the model.
The greater the value of N, the greater the symmetry of the model and the greater the complexity of the magnetic behaviors it describes. Ytterbium atoms have six possible spin states, and the Kyoto simulator is the first to reveal magnetic correlations in a Hubbard SU (6) model. These types of calculations are impossible to calculate on a computer, according to the study.
“This is the real reason for doing this experiment,” Hazzard said. “Because we can’t wait to learn about the physics of this Hubbard SU (N) model.”
Graduate student in Hazzard’s research group and study co-author Eduardo Ibarra-García-Padilla added that the Hubbard model aims to capture the basic ingredients needed for what makes a solid material a metal, an insulator, a magnet or a superconductor. “One of the fascinating questions that experiments can explore is the role of symmetry,” said Ibarra-García-Padilla. “Having the ability to engineer it in a lab is extraordinary. If we can understand this, it could guide us to make real materials with new and desired properties ”.
The team is currently working on developing the first tools capable of measuring behavior that is one billionth of a degree above absolute zero.
“These systems are quite exotic and special, but the hope is that by studying and understanding them, we can identify the key ingredients that must be present in real materials,” concluded Hazzard.