A team of physicists at the University of Bonn in Germany has developed a technique to create optical ‘wells’ for a photonic Bose-Einstein condensate.
The artist’s rendering shows how potential ‘wells’ are created for photons in the microresonator through heating with an external laser beam (green). Image credit: David Dung, University of Bonn.
“Thousands of photons 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. We call this a photonic Bose-Einstein condensate,” explained University of Bonn Professor Martin Weitz and co-authors.
In 2010, the team pioneered a technique for producing a Bose-Einstein condensate from photons.
In the latest study, the physicists experimented with this kind of a ‘super-photon.’
“In the experimental setup, a laser beam was rapidly bounced back and forth between two mirrors,” Professor Weitz said.
“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.”
The researchers used a trick here: they mixed a polymer into the pigment between the mirrors, which changed its refractive index depending on the temperature.
The route between the mirrors for the light thus changed so that longer light wavelengths passed between the mirrors when heated.
The extent of the light path between the mirrors could be varied, in that the polymer could be warmed via a very thin heating layer.
“With the help of various temperature patterns, we were able to create different optical dents,” Professor Weitz said.
“The geometry of the mirror only appeared to warp, while the refractive index of the polymer changed at certain points — however, this had the same effect as a hollow shape. Part of the super-photon flowed into this apparent well.”
In this way, the authors were able to use their apparatus to create different, very low-loss patterns that captured the photonic Bose-Einstein condensate.
They investigated in detail the formation of two neighboring ‘wells,’ controlled via the temperature pattern of the polymer.
“When the light in both optical hollows remained at a similar energy level, the super-photon flowed from one well into the neighboring one,” Professor Weitz explained.
“This was a precursor of optical quantum circuits. Perhaps even complex arrangements, for which quantum entanglement occurs in interaction with a possible photon interaction in suitable materials, can be produced with this experimental setup.”
“This would, in turn, be the prerequisite for a new technique for quantum communication and quantum computers. But that’s still a long way off.”
The research is published in the journal Nature Photonics.
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David Dung et al. Variable potentials for thermalized light and coupled condensates. Nature Photonics, published August 14, 2017; doi: 10.1038/nphoton.2017.139
