Physicists Created 'Slits in Time' and Discovered 'Unexpected Physics' in Experiment

Scientists have discovered “unexpected physics” by opening up “slits” in time, a new study reports, achieving a longstanding dream that can help to probe the behavior of light and pioneer advanced optical technologies.

The mind-boggling approach is a time-based variation on the famous double-slit experiment, first performed by Thomas Young in 1801, which opened a window into the weird probabilistic world of quantum mechanics by revealing the dual nature of light as both a particle and a wave. 

The new temporal version of this test offered a glimpse of the mysterious physics that occur at ultrafast timescales, which may inform the development of quantum computing systems, among other next-generation applications.

In the original version of the double-slit experiment, light passes through two slits that are spatially separated on an opaque screen. A detector on the other side of the screen records the pattern of the light waves that emerges from the slits. These experiments show that the light waves change direction and interfere with each other after going through the slits, demonstrating that light behaves as both a wave and particle. 

This insight is one of the most important milestones in our ongoing journey into the quantum world, and it has since been repeated with other entities, such as electrons, exposing the trippy phenomena that occurs at the small scales of atoms.

Now, scientists led by Romain Tirole, a PhD student studying nanophotonics at Imperial College London, have created a “temporal analogue of Young’s slit experiment” by firing a beam of light at a special metamaterial called Indium Tin Oxide, according to a study published on Monday in Nature Physics. 

Metamaterials are artificial creations endowed with superpowers that are not found in nature. For instance, the Indium Tin Oxide used in the new study can change its properties in mere femtoseconds, a unit equal to a millionth of a billionth of a second. This incredible variability allows light waves to interact with the metamaterial at key moments in ultrafast succession, called “time slits,” which produces a time-based diffraction pattern that is analogous to the results returned in the spatial version of the experiment. 

“Showing diffraction from a double slit in time requires to flick a switch extremely fast, on time scales comparable to how fast the light field oscillates, about a few femtoseconds,” said Tirole in an email to Motherboard. “If the entire history of the universe from the Big Bang to the moment you read this was a second, an oscillation of light would only take the equivalent of a single day!”

“Switching at this speed has long been difficult, but a few years ago a new material, Indium Tin Oxide, which already covers the screens of our mobile phones or televisions, was shown to switch very fast when you shine an intense laser beam on it,” he continued. “This has enabled a rapid progress of the field—see for example a conference we are organizing.”

 In other words, the super-speedy changeability of Indium Tin Oxide finally made a time slit experiment possible, after many years of eluding scientists. To bring this vision to reality, Tirole and his colleagues used lasers to switch the reflectance of the material on and off at high speeds. 

When the material was turned on, it essentially became a mirror that allowed the team to record the diffraction patterns of light beams that interacted with the highly reflective surface. The brief moments when light was reflected off the metamaterial’s mirror state were the so-called time slits that form the basis of the experiment. The separation between these slits determined the pattern of oscillations that were observed by the researchers.

To the team’s astonishment, the results of the experiment revealed more oscillations than predicted by existing theories, as well as far sharper observations, which points to “unexpected physics” in the findings, according to the study.

“When we measured the spectra, we were very surprised by how clear they showed up on the detectors,” Tirole said. “How visible these oscillations are depends on how fast we can switch our metasurface on and off [and] this means that the speed at which our metamaterial changes is much faster than what was previously thought and accepted. This is exciting as it implies that new physical mechanisms are still to be uncovered and exploited.”

“In our experiment we show that this wonder material has an even faster switching speed, 10-100 times faster than previously thought, which enables a much stronger control of light,” he also noted.  

This temporal version of the double-slit experiment altered the frequency of the light, changing its color, which created distinctive patterns in which some colors were enhanced while others were canceled out. The results are similar to the patterns created by the traditional spatial version of the test, which produces light waves that bolster and nullify each other after they have passed through the slits.

The breakthrough paves the way toward new research into the enigmatic properties of light, and the many emerging technologies that rely on optical phenomena. Tirole and his colleagues are especially eager to try to repeat the experiment with a time crystal, a very strange quantum system that has revolutionized many fields in physics. 

“A double slit experiment is the first brick on the road to more complex temporal modulations, such as the much sought time-crystal where the optical properties are temporally modulated in a periodic fashion,” Tirole concluded. “This could have very important applications for light amplification, light control, for example for computation, and maybe even quantum computation with light.”