In a first, CERN scientists carry out laser cooling of Positronium

Physicists representing 19 European and one India research group comprising the Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEgIS) collaboration announced this scientific achievement on Thursday.

An artist impression of the laser cooling setup

The experiment was performed at the European Organization for Nuclear Research, more popularly known as CERN, in Geneva. This is an important precursor experiment to the formation of anti-Hydrogen and the measurement of Earth’s gravitational acceleration on antihydrogen in the AEgIS experiment, they said. In addition, this scientific feat could open prospects to produce a gamma-ray laser that would eventually allow researchers to look inside the atomic nucleus and have applications beyond physics.

During the past few years, several rounds of experimental runs were performed in an accelerator beam hall of the CERN before the AEgIS team tasted success.

Since it was formally accepted as a scientific experiment by CERN in 2008, the setting up of the AEgIS experiment, its construction and commissioning continued through 2012 – 2016. This comprised designing of the complex particle traps used to confine antiparticles, antiprotons and positrons. In 2018, AEgIS became the first in the world to demonstrate the pulsed production of antihydrogen atoms.

An artist impression of positronium

“The experiment was done under the very challenging circumstances of an accelerator beam hall, rather than within the confines of a very well controlled laboratory. In every part of the experiment — be it the input beams, the lasers, laser alignment, timing and control systems, detection techniques, etc. required technological innovations to make the science a reality,” said Professor Sadiq Rangwala, faculty at Raman Research Institute and the lead of the Indian group in the collaboration.

Experimentalists achieved laser cooling of Positronium atoms initially from ~380 Kelvin to ~170 Kelvin, and demonstrated the cooling in one dimension using a 70-nanosecond pulse of the alexandrite-based laser system. The lasers deployed, researchers said, were either in the deep ultraviolet or in the infrared frequency bands.

An artist impression of electron and positron

Physicists involved expect that this experiment will pave the way for performing spectroscopic comparisons required for the Quantum Electrodynamics (QED), the study of the light and its interaction with charged matter, and a possible degenerate gas of Positronium down the road.

According to CERN, the new scientific development will allow high-precision measurements of the properties and gravitational behaviour of this exotic but simple matter–antimatter system, which could reveal newer physics. It also allows the production of a positronium Bose–Einstein condensate, in which all constituents occupy the same quantum state.

“A Bose-Einstein condensate of antimatter would be an incredible tool for both fundamental and applied research, especially if it allowed the production of coherent gamma-ray light with which researchers could peer into the atomic nucleus.” said Ruggero Caravita, spokesperson, AEgIS.

Such a condensate has been proposed as a candidate to produce coherent gamma-ray light via the matter-antimatter annihilation of its constituents – laser-like light made up of monochromatic waves that have a constant phase difference between them, AEgIS said in its statement released on Thursday.