Laser Cooling of Positronium Achieved by CERN

Context: 

In the recently published paper in the Physical Review Letters, the AE¯gIS team has described the laser cooling of Positronium atoms achieved from a Broad-based laser system.

International Collaboration of Physicists Achieves First Successful Laser Cooled Positronium

• The experiment was performed at the European Organization for Nuclear Research, (CERN) Antimatter Factory in Geneva.
• Conducted by: An international team of Physicists representing 19 European and one Indian research group comprising the Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEgIS) collaboration demonstrated the  laser cooling of Positronium.

About Laser Cooling

• Laser cooling is a technique in atomic physics and quantum optics that can slow down and trap atomic and molecular particles. 
• The method is based on the interaction between light and charged matter, and it exploits the way in which photons transfer momentum to atoms.

Working Principle Of Laser Cooling

• It is based on the absorption and re-emission of photons. 
  • When an atom absorbs a photon, its energy is increased, and it moves to a higher energy level. 
  • When it later re-emits the photon, it loses energy and falls back to a lower energy level.
  • The key to laser cooling is to ensure that the atom always re-emits the photon in a direction opposite to its motion. 
  • This means that, on average, the atom loses more momentum to the photons than it gains, and slows down as a result. This allows atoms to be captured in optical traps.
  • This is normally done using a narrow-band laser, which emits light with a small frequency range.
  • The AEgIS team however used a broad-band laser (~380 Kelvin (106.85 degrees Celsius) to ~170 Kelvin (minus 103.15 degrees Celsius), using a 70-nanosecond pulsed alexandrite-based laser system) in their experiment which helped cool the positronium sample.
  • The experiment was carried out without applying any external electric or magnetic field, simplifying the experimental setup and extending the positronium lifetime.

Significance Of Laser Cooling

• Advanced studies in Particle Physics:  It will help to improve understanding of the physical nature, comprising matter and anti-matter facilitated through the interaction between light and charged matter.
• Formation of hydrogen (a positron orbiting an antiproton): This is an important Precursor experiment to the formation of anti-hydrogen and the measurement of Earth’s gravitational acceleration on antihydrogen.
• Open New Avenues: It could open prospects to produce a gamma-ray laser that would eventually allow researchers a look inside the atomic nucleus and may have probable applications beyond physics.
• A ground for Future experiments: To  perform 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 could be achieved.
• New possibilities for antimatter research:  It will allow high-precision measurements of the properties and gravitational behaviour of the simple matter–antimatter system, which could reveal newer physics.
• Bose–Einstein condensate: 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: It would be a tool for fundamental and applied research.
  • 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.

News Source: The Indian Express

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