DATE2024.09.12 #Press Releases

Positronium, the simplest “atom,” can be cooled to cryogenic temperatures in 10 millionths of a second

—The first major step toward unraveling the mysteries of physics through the precise science of atoms, including antiparticles—

Summary

A research group led by Associate Professor Kosuke Yoshioka and Assistant Professor Kenji Shu of the Graduate School of Engineering at the University of Tokyo and Assistant Professor Akira Ishida of the Graduate School of Science at the same university, in collaboration with the High Energy Accelerator Research Organization (KEK) Institute for Materials Structure Science and the National Institute of Advanced Industrial Science and Technology, has achieved the world's first rapid cooling of positronium by laser beam. The research group has realized the world's first rapid cooling of positronium by laser light.

By using an originally developed laser light source, they succeeded in laser cooling of positronium, which had been awaited for 30 years since its theoretical proposal, and proved that it can be made into a gas that is orders of magnitude cooler than conventional gases in just 10 millionths of a second. Physics is riddled with many mysteries, such as the fact that there are few antiparticles left in the universe and the origin of dark matter. To solve this, research is being conducted around the world to verify where the breakdown of the fundamental theory lies. The results of this research will make it possible to investigate to what extent fundamental theories accurately represent reality using the most basic atoms consisting only of electrons and their antiparticles, as well as to precisely study the effects of the mass and gravity of antiparticles.

This research result was selected as one of the Top 10 Breakthroughs of the Year in physics for 2024 by Physics World magazine.

Figure：Conceptual diagram of positronium irradiated by a train of laser beams with rapidly changing wavelengths, which are instantly cooled in a vacuum.

Iinks：UTokyo, Graduate School of Engineering the University of Tokyo, ICEPP, KEK, AIST（in Japanese)

Journal

Journal name	Nature
Title of paper	Cooling positronium to ultra-low velocities with a chirped laser pulse train