Physicists have revealed that just seven quantum particles can behave as if they were in a crowd of billions.
By Rafi Letzter | SPACE.com
At larger scales, matter goes through changes, called phase transitions, in which (for example) water turns into a solid (ice) or a vapor (steam). Scientists were used to seeing this behavior in large masses of molecules, but never in such a tiny cluster.
In a new study, detailed today (Sept. 10) in the journal Nature Physics, researchers witnessed these phase transitions in systems made up of just seven light particles, or photons, which took on an exotic physical state known as a Bose-Einstein condensate (BEC). That’s the physical state that matter can reach at ultracold temperatures, in which particles begin to blend together and act in unison.
Because photons are packets of light, they’re made of energy, not matter, which makes the idea of them going through a phase transition strange. But back in 2010, a team of German researchers showed that light particles could be induced to behave as a BEC would, just like their matter-particle cousins.
To trap the photons, those researchers built a small mirrored chamber and filled it with a colored dye. When the light particles banged into the dye particles, the dye particles would absorb them and re-emit them, so the photons took longer to move through the chamber — effectively slowing them down. When the photons struck the chamber’s mirrored walls, the photons would bounce off without being absorbed or escaping. So the chamber was effectively a space where researchers could make photons sluggish and put them in close quarters. And in that situation, the physicists found, the photons would interact with one another like matter, and exhibit behaviors recognizable as those of a BEC.