Illustration of the double-slit experiment
Russell Kaitley/Science Photo Library
The famous double-slit experiment, which demonstrated that light is both a wave and a particle, was performed using a ‘time-slit’. A related technology presents a new way of manipulating light that can be used to create strange substances called time crystals.
The double-slit experiment, first performed by Thomas Young in 1801, requires a beam of light to hit a plate or card with two small slits cut through it for the light to pass through. As the light waves pass through the slit, they interfere with each other, creating bright and dark stripes on the screen. This is one of his first proofs that light is also a wave, as this would not be possible if light were simply made of particles.
While the original double-slit experiment used two spatially separated slits, Riccardo Sapienza at Imperial College London and his colleagues found that obstacles to light propagation were separated temporally as well. experiment was conducted. “Temporal manipulation of waves is an old subject, but it has been driven mostly by theory for the last 30 years,” he says. “Especially the experiments with light were very difficult.”
This is because conducting such experiments requires a material that can change from transparent to reflective at an extraordinary rate in order to create what the researchers call a “time slit.” Sapienza and his team used a material called indium tin oxide, which is commonly used for coating various electronic displays. When hit by a powerful laser beam, it goes from being almost completely transparent to reflecting most of the light that hits it for a short time.
To perform the experiment, the researchers used two sequential laser pulses to reflect off the material while simultaneously illuminating it with a low-intensity ‘probe’ laser. Light from the probe laser passes through the material when unreflected and bounces off when struck at the same time as the laser pulse.
A measurement of the bounced light showed an interference pattern similar to that seen in the previous version of the experiment, but this time it was in the light frequencies that determined the color, rather than the brightness. “In Young’s experiments, light enters at one angle and leaves at different angles. In our experiments, light enters at one frequency and leaves at different frequencies,” he says. says Sapienza.
This was as predicted by theoretical calculations, but the frequency of light oscillated far beyond researchers’ expectations. Since the frequency depends on the sharpness of the material’s transition from transparent to reflective, this means that the material responded to the laser pulse with incredible speed, within a few femtoseconds of the pulse.1 A femtosecond is one millionth of a billionth of a second.
“The materials reacted 10 to 100 times faster than expected, which was a big surprise,” says Sapienza. “We were hoping to see some vibrations, but we have seen a lot of vibrations.”
This quick transition time can be useful for crafting time crystals. Time crystals are strange substances with moving structures that repeat over and over again. It could also be useful for more everyday applications, says his Maxim Shcherbakov at the University of California, Irvine. “Temporal interference is an exciting discovery that has applications in many state-of-the-art technologies, but especially in telecommunications, where the way signals are processed in time is very important,” he says.
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