From Science News: “Superfluid Motion of Light Observed at Room Temperature”

ScienceNews bloc

Science News

Jun 9, 2017
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An international team of physicists has experimentally demonstrated that superfluid motion of light is possible under ambient conditions. Until now, this phenomenon had only been observed at low cryogenic temperatures.

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Schematic of the organic microcavity used to observe superfluid flow. Image credit: Polytechnique Montreal.

The wave nature of light has been known for centuries. The fact that light can also behave as a liquid, rippling and spiraling around obstacles, is a much more recent finding.

The ‘liquid’ properties of light emerge under special circumstances, when the photons that form the light wave are able to interact with each other.

Physicists from CNR NANOTEC Institute of Nanotechnology in Italy, Polytechnique Montreal in Canada, Aalto University in Finland and Imperial College London in the UK have shown that for light ‘dressed’ with electrons, an even more dramatic effect occurs: light become superfluid, showing frictionless flow when flowing across an obstacle and reconnecting behind it without any ripples.

“Superfluidity is an impressive effect, normally observed only at temperatures close to absolute zero (minus 273 degrees Celsius), such as in liquid helium and ultracold atomic gasses,” said co-lead author Dr. Daniele Sanvitto, from CNR NANOTEC Institute of Nanotechnology.

“The extraordinary observation in our work is that we have demonstrated that superfluidity can also occur at room temperature, under ambient conditions, using light-matter particles called polaritons.”

“Superfluidity, which allows a fluid in the absence of viscosity to literally leak out of its container, is linked to the ability of all the particles to condense in a state called a Bose-Einstein condensate.”

“Something similar happens, for example, in superconductors: electrons, in pairs, condense, giving rise to superfluids or super-currents able to conduct electricity without losses.”

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The flow of polaritons (quasiparticles that result from a coupling between photons and electron-hole pairs in a semiconductor material) encounters an obstacle in the supersonic (top) and superfluid (bottom) regime. Image credit: Polytechnique Montreal.

“To achieve superfluidity at room temperature, we sandwiched an ultrathin film of organic molecules between two highly reflective mirrors,” explained Dr. Stéphane Kéna-Cohen, of Polytechnique Montreal.

“Light interacts very strongly with the molecules as it bounces back and forth between the mirrors and this allowed us to form the hybrid light-matter fluid.”

“In this way, we can combine the properties of photons such as their light effective mass and fast velocity, with strong interactions due to the electrons within the molecules.”

“Under normal conditions, a fluid ripples and whirls around anything that interferes with its flow. In a superfluid, this turbulence is suppressed around obstacles, causing the flow to continue on its way unaltered.”

The researchers said: “the fact that such an effect is observed under ambient conditions can spark an enormous amount of future work, not only to study fundamental phenomena related to Bose-Einstein condensates with table-top experiments, but also to conceive and design future photonic superfluid-based devices where losses are completely suppressed and new unexpected phenomena can be exploited.”

The research is published in the journal Nature Physics.

See the full article here .

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