Researchers from the ALPHA collaboration at CERN were able, for the first time, to cool anti-hydrogen atoms using laser light. Anti-hydrogen is the simplest form of atomic antimatter, and the technique known as laser cooling was first demonstrated four decades ago in normal matter. Laser cooling is commonly used in many fields of research.
The first application of laser cooling for anti-hydrogen opens the door to more accurate measurements of the internal structure of anti-hydrogen and how it behaves under the influence of gravity. Comparing the measurements with those of normal hydrogen atoms can reveal differences between the atoms of matter and antimatter. These differences, if present, could help researchers determine why the universe is composed only of matter, an imbalance known as matter-antimatter asymmetry.
The project’s researchers say the ability to cool laser anti-hydrogen atoms is a game changer for spectroscopic and gravitational measurements. The new capability could lead to new perspectives in antimatter research, including the creation of antimatter molecules and the development of anti-atom interferometry. Jeffrey Hangst, an ALPHA spokesman, says cooling laser antimatter was science fiction about a decade ago.
The team creates its anti-hydrogen atoms, but taking antiprotons from the CERN Antiproton Decelerator and linking them to positrons originating from a sodium-22 source. The anti-hydrogen atoms produced are confined in a magnetic trap, preventing them from coming into contact with matter. The researchers say that the measurement of anti-hydrogen behavior within the Earth’s gravitational field is limited by the kinetic energy or, equivalently, the temperature of the anti-atoms.
Laser cooling helps to control the temperature of the anti-atoms. Antiatomas absorb laser photons, causing them to reach a state of greater energy. They then emit photons and spontaneously decay back to their initial state. The interaction depends on the speed of the atoms and, once the photons give impulse, the repetition of the absorption-emission cycle leads to the cooling of the atoms at a low temperature.