Feb 28, 2024 15:19:00

A team from the University of Tokyo successfully cooled an exotic atom made of antimatter, ``positronium,'' to near absolute zero.

A research team from the University of Tokyo and the European Organization for Nuclear Research (CERN) has announced that they have succeeded in cooling

positronium , an exotic atom made of antiparticles, by using laser light to lower the temperature of an object. They were announced one after another. This finding, which slows down antimatter systems and allows them to be studied in more detail, could be useful in research in a wide range of fields, from the grand quest for the beginning of the universe to quantum mechanics, which reveals the microscopic world. It is expected.

[2310.08761] Laser cooling of positronium
https://arxiv.org/abs/2310.08761

Phys. Rev. Lett. 132, 083402 (2024) - Positronium Laser Cooling via the 1 ³ S−2 ³ P Transition with a Broadband Laser Pulse
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.083402

AEgIS experiment paves the way for new set of antimatter studies by laser-cooling positronium | CERN
https://home.cern/news/news/experiments/aegis-experiment-paves-way-new-set-antimatter-studies-laser-cooling

Breakthrough: Positronium Cooled By Laser in a World First : ScienceAlert
https://www.sciencealert.com/breakthrough-physicists-cooled-antimatter-to-near-absolute-zero-for-the-first-time

Positronium is an atom made up of a negatively charged electron and its opposite, the positron. Also, when positronium and antiprotons collide, the positrons of positronium and antiprotons combine to produce antihydrogen.

For this reason, positronium is ideal for experiments investigating the properties of antimatter, but it is extremely unstable and annihilates into gamma rays in just 142 billionths of a second. Moreover, positronium produced in a cloud of particles flies around at various speeds, making it difficult to pinpoint its location.

One solution to this problem is

laser cooling technology, which uses a laser to reduce the momentum of particles and lower their temperature. When you shine a laser on a particle, a photon is absorbed, adding energy, but then emitted, losing energy. By repeating this process, the technology slows down the particles to speeds that would normally be unattainable, making it possible to more accurately capture the characteristics of the target.

The research team behind the AEgIS experiment at CERN used broadband laser cooling to target a wide velocity distribution, lowering the temperature of positronium from 380 Kelvin (approximately 106 degrees Celsius) to 170 Kelvins (approximately minus 103 degrees Celsius). It was very successful. The research team plans to aim to break through the 10 Kelvin barrier in the future.

by CERN - Politecnico di Milano

Furthermore, a research team led by

Kenji Chou from the University of Tokyo used a laser cooling technique called 'chirp cooling,' which adjusts the laser frequency to match the particle's speed, to reduce the temperature of positronium to absolute zero, 0 Kelvin ( By lowering the temperature to about 1 Kelvin (about -272 degrees), which is close to -273.15 degrees, the overall velocity and distribution of electrons and positrons was significantly reduced.

Although the research of both teams is independent, they have shared their results regarding laser cooling of positronium. posted the paper on the preprint server arXiv on the same day.

Antimatter holds many possibilities, including mysteries regarding the formation of the universe. When the universe was formed with the Big Bang, equal amounts of normal matter and antimatter should have been created in the universe, but the current universe is mostly made of matter. If we can learn more about the behavior of antimatter using the cooling technology established this time, it may provide important clues in investigating the whereabouts of the missing antimatter.

Scientists also want to create Bose-Einstein condensates (BECs) of positronium. Bose-Einstein condensation is a phenomenon in which when a cloud of particles is cooled to the very edge of absolute zero, it becomes like one gigantic elementary particle. The BEC of positronium emits coherent gamma rays through the annihilation of matter and antimatter, which is a very powerful tool in elucidating the fundamental structure of atoms.

Ruggero Calavita, CERN's AEgIS spokesperson, said: 'If antimatter BECs can produce coherent gamma-ray light that allows researchers to peer into the nucleus of an atom, it will be a great opportunity for basic research and applications. It will be a great tool for both research.'