Exotic quantum states made from light

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are sufficiently concentrated and cooled. The individual particles merge with each other, making them indistinguishable. Researchers call this a photonic Bose-Einstein condensate. It has long been known that normal atoms form such condensates. Prof. Martin Weitz from the Institute of Applied Physics at the University of Bonn attracted attention among experts in 2010 when he produced a Bose-Einstein condensate from photons for the first time.

In his latest study, Prof. Weitz' team experimented with this kind of super-photon. In the experimental setup, a laser beam was rapidly bounced back and forth between two mirrors. In between was a pigment that cooled the laser light to such an extent that a super-photon was created from the individual light portions. "The special thing is that we have built a kind of optical well in various forms, into which the Bose-Einstein condensate was able to flow," reports Weitz.