International collaboration of physicists demonstrates laser cooled Positronium

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Last Updated25/02/2024

An international collaboration of researchers from the Anti-hydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEgIS), has achieved a significant milestone by successfully demonstrating the laser cooling of Positronium.

It is a fundamental atom composed of an electron (e-) and a positron (e+), both being leptons that interact through electromagnetic and weak forces.
With a very short life, it annihilates with a half-life of 142 nanoseconds.
It is considered a pure leptonic atom.
- Unlike usual atoms that contain a mixture of baryons and leptons, Positronium solely consists of electrons and positrons.
Its hydrogen-like system, with halved frequencies for excitation, makes it an ideal candidate for attempting laser cooling and performing tests of fundamental physics theories.

The AEgIS experiment was formally accepted by CERN in 2008, with construction and commissioning continuing through 2012-2016.
It involves physicists from 19 European groups and one Indian group.
- Professor Sadiq Rangwala from Raman Research Institute (RRI) in Bengaluru is leading the Indian effort.
The experiment was conducted at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland.
Significance: Serves as a crucial precursor to the formation of anti-hydrogen and the measurement of Earth’s gravitational acceleration on antihydrogen in the AEgIS experiment.

The AEgIS team successfully cooled Positronium atoms from ~380 Kelvin to ~170 Kelvin.
A 70-nanosecond pulse of the alexandrite-based laser system was used to demonstrate cooling in one dimension.
Lasers deployed were either in the deep ultraviolet or infrared frequency bands.

Laser cooling of anti-atoms like Positronium and their spectroscopic comparison are crucial tests for Quantum Electro Dynamics (QED).
This achievement opens doors for creating exotic many-particle systems like Bose-Einstein condensates.