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Physicists have revealed that only seven quantum particles can behave as if they were in a crowd of billions.
On a larger scale, the material undergoes changes, called phase transitions, in which (for example) the water is transformed into solid (ice) or vapor (vapor). Scientists were used to seeing this behavior in large masses of molecules, but never in such a small cluster.
In a new study, detailed today (Sept. 10) in the journal Nature Physics, researchers have witnessed these phase transitions in systems composed of only seven light particles, or photons, that took on an exotic physical state called Bose-Einstein condensate. (BEC). It is the physical state that the material can reach at ultra-cold temperatures, in which the particles begin to mix and act in unison.
Because photons are light packets, they are made of energy, no matter, making it strange idea to go through a phase transition. But in 2010, a team of German researchers showed that light particles could behave as a BEC would, just like their particle-particle cousins.
To trap the photons, these researchers built a small mirrored chamber and filled it with a colored dye. When the light particles got stuck in the dye particles, the dye particles absorbed them and re-emitted them, so that the photons took longer to move around the chamber – effectively slowing them down. When the photons hit the walls of the chamber, the photons would rebound without being absorbed or escape. The room was a space where researchers could slow photons and put them aside. And in this situation, physicists have discovered that photons interact with each other like matter and exhibit recognizable behaviors as those of a BEC.
In more recent experiment, the researchers wanted to determine the minimum number of photons needed for this to happen. Using a finely tuned laser, they pumped photons into a dye-filled mirror trap, one at a time, and observed the concoction to determine the emergence of a BEC. They found that after an average of only seven photons, the photons formed a BEC – they began to act as a particle. This is a new low bar for the number of particles needed for a phase transition. [The Coolest Little Particles in Nature]
"Now that it is confirmed that the" phase transition "is still a useful concept in such small systems, we can explore properties that would not be possible in larger systems," said Robert Nyman, physicist at Imperial College London. A declaration.
The researchers noted that micro-BECs and phase transitions involving larger groups of particles showed some differences. When the ice is warming beyond its melting point, it seems to instantly switch from a solid form to a liquid form, with no intermediate stage. The same is true for most phase transitions of most chemicals. But the seven – photon BEC appeared to be forming a little more gradually, the researchers said in the statement, rather than at once.
Yet they wrote in the article that the photonic phase transition has shown that even at very small scales, phase transitions look remarkably like what happens on a large scale. Physics is physics, all the way down.
Originally published on Live Science.
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