By Amit Malewar 12 Sep, 2024
Collected at: https://www.techexplorist.com/antimatter-scientists-cool-positronium-near-absolute-zero/89488/
Positronium is an exotic atom with a single negative electron and a positively charged antimatter positron. It has a very short life.
Using carefully tuned lasers, scientists from the University of Tokyo successfully cooled and slowed down samples of Positronium. Their study is expected to help explore exotic forms of matter to unlock secrets of antimatter.
The collision of matter and antimatter annihilates them. It is widely believed that they were created in equal amounts at the dawn of time, but scientists have not seen this.
Associate Professor Kosuke Yoshioka from the Photon Science Center said, “We have successfully slowed and cooled down exotic atoms of Positronium, which is 50% antimatter. This means that, for the first time, it can be explored in previously impossible ways, which will necessarily include a deeper study of antimatter.”
Despite having a concise lifespan, Positronium is a real thing. It has a central, positively charged, and relatively large proton and tiny, negatively charged electron in orbit, except you swap the proton for the antimatter version of the electron, the positron.
This creates an exotic atom that is electrically neutral and doesn’t have a big nucleus. Instead, an electron and a positron orbit each other, making it a two-body system. As it is a two-body system, it can be described entirely by traditional mathematical and physical theories, making it ideal to test predictions with extreme accuracy.
Yoshioka said, “For researchers like us involved in precision spectroscopy, being able to examine the properties of cooled positronium precisely means we can compare them with precise theoretical calculations of its properties.”
“Positronium is one of the few atoms made up entirely of only two elementary particles, which allows for such exact calculations. The idea of cooling Positronium has been around for around 30 years. Still, a casual comment by undergraduate student Kenji Shu, now an assistant professor in my group, prompted me to take on the challenge of achieving it, and we finally did.”
During the experiment, scientists overcame several difficulties. Firstly, it has a short life: one-ten millionth of a second. Secondly, its extreme light mass. As it’s so lightweight, you can’t use a cold physical surface or other substance to cool Positronium down, so the team used lasers.
The team used a weak and finely tuned laser to gently push a positronium atom in the opposite direction of its movement. This slowed down the Positronium and also cooled cooled it.
By repeating this process very quickly, within one ten-millionth of a second, scientists cooled parts of positronium gas to just 1 degree above absolute zero (-273°C), the coldest possible temperature. This is a massive drop from the gas’s initial temperature of 600 Kelvin (327°C), achieved quickly.
“Our computer simulations based on theoretical models suggest that the positronium gas might be even colder than we can currently measure in our experiments. This implies that our unique cooling laser is very effective at reducing the temperature of Positronium, and the concept can hopefully help researchers study other exotic atoms,” said Yoshioka.
“This experiment used a laser in just one dimension, however, and if we utilize all three, we can measure the properties of Positronium even more precisely. These experiments will be significant because we may be able to study the effect of gravity on antimatter. If antimatter behaves differently to regular matter due to gravity, it could help explain why some of our universe is missing.”
Journal Reference:
- Kosuke Yoshioka, Cooling Positronium to ultralow velocities with a chirped laser pulse train, Nature (2024). DOI: 10.1038/s41586-024-07912-0
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