Recreating the double slit experiment that demonstrated the wave nature of light in time, rather than space

Imperial physicists have recreated the famous double slit experiment, which showed that light behaves as a particle and a wave, in time rather than space.

The experiment relies on materials that can change their optical properties in fractions of a second, which could be used in new technologies or to explore fundamental questions in physics.

The original double-slit experiment, performed by Thomas Young at the Royal Institution in 1801, showed that light acts as a wave. However, further experiments have shown that light actually behaves both as a wave and as a particle – revealing its quantum nature.

These experiments had a profound impact on quantum physics, revealing the double particle and wave nature of not just light, but other “particles” including electrons, neutrons and whole atoms.

Now, a team led by physicists from Imperial College London has conducted the experiment using “rifts” in time rather than space. They achieved this by shooting light through a material that changes its properties in a fraction of a second (four millionths of a second), allowing the light to pass through at precise times in rapid succession.

Lead researcher Professor Riccardo Sapienza, from Imperial’s Department of Physics, said, “Our experiment reveals more about the fundamental nature of light while serving as a starting point for creating the ultimate materials that can precisely control light in both space and time.”

Details of the trial were published today (April 3) in nature physics.

The original double-slit setup involved directing light onto an opaque screen with two thin parallel slits in it. Behind the screen was a detector of light passing through it.

To travel through the slits as a wave, the light splits into two waves that pass through each slit. When these waves cross again on the other side, they “interfere” with each other. When wave crests meet, they reinforce each other, but when crests and troughs meet, they cancel each other out. This creates a striped pattern on the detector of areas of more light and less light.

The light can also be broken down into “particles” called photons, which can be recorded hitting the detector one by one, gradually building up the striped interference pattern. Even when the researchers fired just one photon at a time, the interference pattern continued to appear, as if the photon split in two and traveled through both slits.

In the classical version of the experiment, the light coming out of the physical slits changes direction, so the interference pattern is written in the angular profile of the light. Instead, the time slits in the new experiment change the frequency of the light, which changes its colour. This created colors of light that overlapped each other, enhancing and canceling out certain colors to produce an interference-type pattern.

The material the team used was a thin film of indium tin oxide, which makes up most cellphone screens. The reflection of the material has been altered by the lasers on ultra-fast timescales, creating “slits” of light. The material responded much faster than the team expected to control the laser, and varied its reflectivity within a few femtoseconds.

Matter is a metamaterial – engineered to have properties not found in nature. Such precise control of light is one of the promises of metamaterials, and when combined with spatial control, could create new techniques and even analogues for studying fundamental physical phenomena such as black holes.

Co-author Professor Sir John Pendry said, “The double temporal slits experiment opens the door to an entirely new spectral analysis capable of resolving the temporal structure of a light pulse on the scale of a single period of radiation.”

The team next wants to explore this phenomenon in a “time crystal,” which is similar to an atomic crystal, but where the optical properties vary over time.

Co-author Professor Stefan Meyer said, “The concept of time crystals has the potential to lead to balanced ultrafast optical switches.”