In June 2017, physicists pioneered the production of "liquid light" at room temperature, making this strange form of matter more accessible than ever.
Such matter is both a superfluid substance with zero friction and viscosity and a type of Bose-Einstein condensate, sometimes described as the fifth state of matter, allowing light to actually flow around objects and corners.
Ordinary light behaves like a wave and sometimes like a particle, always traveling in a straight line. This is why we cannot see what is behind corners or objects. But under extreme conditions, light is able to behave like a liquid and flow around objects.
Bose-Einstein condensates are interesting to physicists because in this state the rules switch from classical to quantum physics and matter begins to acquire more wave-like properties. They form at temperatures close to absolute zero, and exist for only a fraction of a second.
However, in a new study, scientists reported the creation of a Bose-Einstein condensate at room temperature using a "Frankenstein-like" combination of light and matter.
Polariton flux colliding with an obstacle in non-superfluid (top) and superfluid (bottom) states / Polytechnique Montreal.
“An extraordinary observation in our work is that we have demonstrated how superfluidity can also occur at room temperature under ambient conditions using particles of light and matter - polaritons,” says lead researcher Daniel Sanvitto of CNR NANOTEC, Italy's Nanotechnology Institute.
The creation of polaritons required serious equipment and nanoscale engineering. Scientists laid a 130-nanometer layer of organic molecules between two ultra-reflective mirrors and hit it with a laser pulse of 35 femtoseconds (one femtosecond is a quadrillion second).
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“This way we can combine the properties of photons, such as their light-efficient mass and high speed, with strong interactions due to protons inside the molecules,” says Stephen Kena-Cohen of the Ecole Polytechnique de Montreal.
The resulting "super-fluid" showed rather unusual properties. Under standard conditions, the fluid creates ripples and eddies when flowing. However, in the case of superfluid, things are different. As shown in the image above, usually the polariton flux is disturbed like waves, but not in a superfluid:
“In a superfluid, this turbulence is not suppressed around obstacles, allowing the flow to continue unchanged,” explains Kena-Cohen.
The researchers argue that the results open up new possibilities not only for quantum hydrodynamics, but also room-temperature polariton devices for future technologies - for example, for the production of superconducting materials for solar panels and lasers.
Vladimir Mirny
