Reimagining the double-slit experiment: Time as a new dimension for the control of light

"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. 

This could have very important applications for light amplification, light control, for example, for computation, and maybe even quantum computation with light," said Romain Tirole, a Ph.D. student from Imperial College London, in an interview with IE. Tirole was part of a research team that explored the double-slit experiment using time.  

In the following sections, we will explore how this research group built on the legacy of Young's experiment to create a new experiment using temporal slits and metamaterials. Their findings have opened up new possibilities for controlling light and exploring the fundamental nature of the universe.

History of the double-slit experiment 

Young presented his work “On the theory of colours and light" in 1801 at the Royal Society. In this, he detailed various interference experiments, including his now-famous slit experiment. Young was severely criticized at the time for arguing with Newton's idea that light was a particle.

Young's original setup, which only consisted of a single slit, used a piece of paper with a hole to allow sunlight to stream through as the light source. He then used a card to split the beam into two. These two beams of light interfered with each other to form an interference pattern on the wall.

The modern experimental setup consists of a beam of light passing through two slits and creating an interference pattern. Although the original experiment was designed to demonstrate the wave nature of light, it has since been used for many important discoveries.

Perhaps, the most significant has been to prove the wave-particle duality of electrons. In 1826, Clinton Davisson and Lester Germer used a stream of electrons (instead of light) in the double-slit experiment. The electrons formed a diffraction pattern on the screen after bouncing off from nickel, confirming that electrons had both wave and particle-like properties. This has since been extended to atoms and molecules.

Today, the wave-particle duality is a cornerstone of quantum mechanics. The double-slit experiment remains one of the most important and widely used tools for studying the behavior of waves and particles in the quantum realm.

Reimagining the double-slit experiment

In recent years, researchers have built on the legacy of Young's experiment to create new experiments. One such group, including Tirole from Imperial College London, has explored the double slit experiment in time. The research team also included Stefano Vezzoli, a Postdoctoral fellow at Imperial College London, and Riccardo Sapienza, a Professor in Physics at Imperial College London. The team's findings were published in Nature Physics.

IE spoke to Tirole about the team's work. According to Tirole, the team's shift to study the control of light using time resulted from the COVID-19 pandemic. 

"We have been working in nanophotonics, the science of light in nanostructure, for many years. During the COVID-19 crisis, we experienced trouble accessing the laboratory and fabricating our samples, but it also gave us an opportunity for reflection.

This pushed us to design experiments to unlock time as a new dimension for the control of light and, in particular, scattering from a temporal particle (a particle that exists only for a short time). Two years later, it turned out that light interacting with two temporal particles, the time slits, is easier to understand," said Tirole, explaining the team's motivation behind the study.

The experimental setup

The team used "time slits" instead of the traditional physical slits to observe the interference pattern. To create these slits, they used a thin indium tin oxide (ITO) film, commonly used in touch screens and LEDs. 

The reflectivity of the ITO film was modified by using lasers on ultrafast timescales. The lasers created tiny slits in the material, allowing light to pass through at specific times. The ITO thin film had a quick response time, with the reflectivity varying within a few femtoseconds.

The interference thus created was due to the changing frequency of light passing through the time slits, as opposed to the changing wavelength, as in the traditional experiment. 

Apart from the time slits, the ITO metamaterial is also a point of interest. Metamaterials are artificially engineered to have properties that are not found in nature. The fine control of light is a promising feature of metamaterials and could lead to new technologies. 

"This could have very important applications for light amplification, light control, for example, for computation, and maybe even quantum computation with light," explained Tirole speaking of the possible impact of their research on the future of physics.

Future research: Time crystals and beyond

"An important word of warning is that, albeit we have clear proof of light color control and temporal diffraction, this comes at the price of a very large and complex laser lab. 

We are still a long way from practical applications, for example, in a smaller device as a laser pointer. But as science has always shown us, more breakthroughs could be behind the corner," explained Tirole, speaking of future applications of their findings.

Despite the technology being very far from real-world applications, time crystals are the most exciting area of research that could be impacted. Time crystals are a new area of research, causing quite a stir in the scientific community. They are a unique type of matter that shows a periodic motion in time, unlike most forms of matter that have periodic motion in space.

Time crystals could be used for highly accurate time measurements or as a memory for quantum computers, among other things. However, the research is still in the early days, as their existence was only first theorized in 2012. 

Nanophotonics, or the manipulation of light at nanoscales, is another field that could be impacted by this research and one that Tirole and the team are already working on. This could lead to the developing of new devices and technologies, such as solar cells, high-speed computers, and optical fibers.

Discussing the scope of future research building on the current work, Tirole thinks there are still many challenges to tackle. "How do we make this shaping of the color of light more efficient? At the moment, we still require high energies for the experiment. These high energies can also burn our sample! 

Luckily, ITO is very resistant, but other materials may not display this tolerance for high heat. Another interesting point lies in the dynamics: how do we make the modulation faster and faster? We don’t fully understand how the material behaves under optical illumination yet, and there are problems linked to how slow the system relaxes after being excited," he concluded.

It seems like there are still several questions that need to be answered before this technology becomes available to us, maybe even in everyday objects like laser pointers!

Conclusion

The double-slit experiment has become one of the foundational experiments that continues to impact the world two centuries later. Recent work by Tirole and his team has put a new spin on this experiment, using time slits to control light. This research could have a significant impact on many different fields.

The path to knowledge in science is unpredictable, and it can be as simple as modifying a centuries-old experiment to obtain new and exciting results!