In 1801, British scientist Thomas Young performed a ‘double slit’ experiment that has gone down in the history of physics: by shining light through two slits in a material, he showed that light behaves like a wave, taking different paths simultaneously only to interfere. Once they recombine in predictable ways.
Since that pioneering moment, the experiment has been repeated to show electromagnetic radiation exhibits both wave-like and particle-like behavior. To put it another way, light can act like a marble rolling down a slope and like a ripple in a pond, depending on how it’s measured.
It’s not just photons that work this way. Scientists have used a similar setup to show that electrons, neutrons and whole atoms behave in the same fashion, establishing a key principle of quantum physics as a theory based on probability.
Now scientists have recreated Young’s experiment with a modern twist. Instead of a pair of slits separated in space, they used ‘time slits’ created by rapid adjustments to the reflection of a material, testing the ability of light waves to interfere with their own past and future.
“Our experiment reveals more about the fundamental nature of light while serving as a stepping stone toward creating the ultimate materials that can control light in both space and time.” said Physicist Ricardo Sapienza from Imperial College London, UK.
Sapienza and his colleagues used a thin layer of indium tin oxide, a material used in smartphone screens. The laser pulse changes its reflection to create two distinct periods in which the light hitting the material can be measured, providing distinct paths in time in which a single wave of light can interfere with itself.
These differences over time change the frequency of light as it hits the material, creating distinct colors rather than differences in brightness with interference between different wavelengths. Scientists studied this interference pattern to make observations about the wave-like behavior of light.
“The double time slit experiment opens the door to an entirely new spectroscopy capable of resolving the temporal structure of a light pulse.” said Physicist John Pendry from Imperial College London.
Interestingly, the slits opened much faster than scientists expected – between 1 and 10 femtoseconds (a quarter of a second). The experiment, which goes beyond theoretical modeling, suggests that part of that modeling needs to be rethought: Materials certainly don’t interact with light exactly the way scientists thought (when the intensity or speed changes, for example).
Having such material, which can change the way it reacts to light on a minute scale, could be useful in developing new technologies and digging deeper into the mysteries of quantum physics.
It is also going to be useful on the largest scale in studying phenomena like black holes. Next, the team applied their ‘time twist’ to another material, atomic crystals, where the atoms are arranged in a rigid pattern – which could lead to rapid advances in electronics.
“The time crystal concept has the potential to lead to ultrafast, parallel optical switches,” said Physicist Stephen Mayer from Imperial College London.
The study was published Nature Physics.