Scientists create 'slits in time' in mind-bending physics experiment

Researchers used lasers to recreate the well-known double slit experiment, but their slits are in time rather than space.

For the first time, researchers have demonstrated the ability to send light through "slits" in time.

In the new experiment, light is shone through two slits in a screen to produce a novel diffraction pattern over space, where the peaks and troughs of the light wave add up or cancel out. This experiment updates a demonstration that dates back 240 years. In the latest work, scientists produced a comparable temporal pattern, basically altering the hue of an ultrashort laser pulse.

The discoveries open the door to improvements in analog computers, which manage data encoded on light beams rather than digital bits; they may even enable such computers to "learn" from the data. Additionally, they enhance our comprehension of the fundamental properties of light and how it interacts with various materials.

Indium tin oxide (ITO), the substance used in the majority of phone screens, was employed in the new study, which was published on April 3 in the journal Nature Physics. ITO can transition from transparent to reflective in reaction to light, as scientists already knew, but the researchers discovered it happens far more quickly than previously believed—in less than 10 femtoseconds. (10 millionths of a billionth of a second).

Riccardo Sapienza, a physicist at Imperial College London and the study's principal author, told Live Science, "This was a really huge surprise and at the beginning it was something that we couldn't understand. By carefully examining the idea of how the electrons in ITO react to incoming light, the researchers eventually discovered why the reaction occurred so quickly. But it took us a while to figure it out.

changing space for time

In 1801 English physicist Thomas Young used the now-famous "double-slit" experiment to show that light behaves like a wave. The waves on a screen with two slits change direction when light shines on it, causing the waves coming through one slit to fan out and cross over the waves coming through the other. An interference pattern is produced when the peaks and troughs of these waves either add up or cancel out, producing brilliant and dark fringes.

In the latest research, Sapienza and associates used an ITO-coated screen and a "pump" laser pulse to simulate an interference pattern over time. Although the ITO was initially clear, the laser's light caused the electrons there to change their characteristics, making the material reflect light like a mirror. This momentary alteration in the optical characteristics would then be seen as a few hundred femtosecond-long slit in time by a subsequent "probe" laser beam striking the ITO screen. The material behaved as though it had two time-dependent slits, simulating light traveling through spatial double slits, when a second pump laser pulse was applied.

When light travelled through these twin "time slits," it varied in frequency, which is inversely proportional to its wavelength, as opposed to traveling through ordinary spatial slits, which cause light to shift direction and fan out. The color of visible light is determined by its wavelength.

Fringes or extra peaks in the frequency spectra, which are graphs of the observed light intensity at various frequencies, appeared in the new experiment as the interference pattern. The spacing of the interference fringes in the frequency spectra is determined by the lag between the temporal slits, just as changing the distance between spatial slits alters the interference pattern that results. It also tells how rapidly the ITO characteristics are changing by how many fringes in these interference patterns can be seen before their amplitude drops to background noise; materials with slower responses produce fewer discernible interference fringes.

It's not the first time that researchers have discovered a way to control light through time rather than just space. In contrast to atoms being organized in a periodic pattern throughout space, Google scientists claim that their quantum computer "Sycamore" developed a time crystal, a new phase of matter that changes regularly in time.

A physicist at The City University of New York named Andrea Alù(opens in new tab), who was not engaged in these tests but has carried out other investigations that resulted in light reflections in time, called it yet another "neat demonstration" of how time and space may be interchangeable.

Alù told Live Science via email that the experiment's most surprising feature is how it shows how we can quickly and significantly change the material (ITO)'s permittivity, which describes how much a material transmits or reflects light. This demonstrates that this substance is a prime candidate for showing time reflections and time crystals.

The goal of the research is to develop metamaterials—structures made to specifically and frequently intricately modify the course of light—using these phenomena.

As of until, these metamaterials have remained static, necessitating the use of a whole new metamaterial structure, such as a new analog computer for each distinct sort of calculation, according to Sapienza.

"Now that we have a material that we can reconfigure, we can use it for multiple purposes," Sapienza added. He continued by saying that such technology may allow for brain-like neuromorphic computing.