Light, which can travel as fast as 300,000 kms/sec in a vacuum, can apparently be stopped dead in its tracks.
Using “exceptional points”, scientists Tamar Goldzak, Alexei A. Mailybaev, and Nimrod Moiseyev, have proposed a theoretical way to slow light to a complete stop. The process involves trapping light inside crystals or ultracold clouds of atoms
A paper published in the Physical Review Letters outlines that previous theoretical attempts have seen light slow at an immense rate, but never to an absolute stop.
Almost twenty years ago, light was slowed down to less than 10−7 of its vacuum speed in a cloud of ultracold atoms of sodium. Upon a sudden turn-off of the coupling laser, a slow light pulse can be imprinted on cold atoms such that it can be read out and converted into a photon again. In this process, the light is stopped by absorbing it and storing its shape within the atomic ensemble. Alternatively, the light can be stopped at the band edge in photonic-crystal waveguides, where the group speed vanishes.
Light can also be released and accelerated buck to normal speed by reversing their gain/loss parameters. The entire process has been described as “driving a car into an icy two-lane tunnel, in which one slides around wildly, but from which one always comes out on the correct side of the road.”
Here, we extend the phenomenon of stopped light to the new field of parity-time (PT) symmetric systems. We show that zero group speed in PT symmetric optical waveguides can be achieved if the system is prepared at an exceptional point, where two optical modes coalesce. This effect can be tuned for optical pulses in a wide range of frequencies and bandwidths, as we demonstrate in a system of coupled waveguides with gain and loss.
What all of this jargon really means, is that exceptional points open up new possibilities for controlling waves, and that is very exciting. Professor Stefan Rotter (Institute for Theoretical Physics, TU Wien) compares this find to classical mathematics “just like complex numbers have brought us new possibilities in mathematics, complex exceptional points give us new ideas for the physics of waves. I am sure that we will soon hear a lot more about exceptional points in many different areas of physics”.
In the past exceptional points have been shown to exhibit strange characteristics when investigated. Lasers have been seen to switch on, even though energy is taken away from them, light is being emitted only in one particular direction, and waves which are strongly jumbled emerge from the muddle in an orderly, well-defined state. The future of exceptional point research is sure to have some wacky consequences.