New theory let’s scientists bring light to a standstill

Light is famously fast, normally travels at nearly 300,000 kilometres per second through space, but now, months after scientists turned light into a frictionless superfluid, and the recent unveiling of what many regard to be the world’s first true living hologram, scientists have proposed a new way to go one step better and bring it to a complete standstill.

In 2001 researchers worked out how slow light down to a fraction of its original speed by trapping it in a cloud of ultra-cold sodium atoms, and elsewhere another team found another way to achieve the same result by slowing light down using materials called photonic crystals.

Now in the journal Physical Review Letters, scientists from Brazil and Israel, have outlined another theoretical method that makes use of a phenomenon termed “Exceptional points”.

Exceptional points are when two different varieties or modes of light waves come together and combine, or coalesce, into one mode. When this happens, light stops in its tracks, but in most systems up until now most of the light itself is also lost at these exceptional points.

In their new paper, Dr Tamar Goldzak and Dr Nimrod Moiseyev at the Technion – Israel Institute of Technology, and Dr Alexei Mailybaev of Brazil’s Institute for Pure and Applied Mathematics, proposed a way to stop light waves while preventing this loss of light using waveguides that make use of a phenomenon called “Parity Time Symmetry”.

A waveguide is a physical object that, as its name suggests, is used to guide the movement of waves. An optical fibre is an example of a waveguide that’s used to transmit telephone signals, and according to the scientists, waveguides could be used to adjust the two waves of light travelling through them so that they balance each other out exactly.

This would mean the light intensity remains constant as it approaches the exceptional point and stops.

“In our paper we show that the group velocity vanishes, that is to say a light pulse is fully stopped if the waveguide is designed exactly at the exceptional point,” say the researchers in their paper.

They suggested that the parameters could be tuned to work at any frequency of light, and that it could also work with other types of waves beside light, such as sound, but while this work was entirely theoretical, for now, in the future it could have the potential to create new practical, technological applications, such as helping to create new, and better, types of Photonic Computing devices, or faster Quantum Computers and communications systems.

“This result opens conceptually new possibilities for designing slow light devices, which exploit generic properties of the exceptional point and, therefore, may offer much larger freedom for technical implementation and operational capability,” the researchers wrote.