The original double-slit experiment, performed in 1801 by Thomas Young at the Royal Institution, showed that light behaves like a wave, contradicting Newton’s corpuscular or particle-like nature of light. Later experiments, however, showed that light actually behaves as both a wave and as particles—revealing its quantum nature.
A team led by Imperial College London physicists performed the experiment using ‘slits’ in time rather than space, the college said on April 3. They achieved this by firing light through a material that changes its properties in femtoseconds (quadrillionths or 10-15 of a second), only allowing light to pass through at specific times in quick succession.
Lead researcher Professor Riccardo Sapienza said: “Our experiment reveals more about the fundamental nature of light while serving as a stepping stone to creating the ultimate materials that can minutely control light in both space and time.” Details of the experiment were published in Nature Physics.
The original double-slit setup involved directing light at an opaque screen with two thin parallel slits in it. Behind the screen was a detector for the light that passed through.
To travel through the slits as a wave, light splits into two waves that go through each slit. When these waves cross over again on the other side, they ‘interfere’ with each other. Where peaks of the wave meet, they enhance each other, but where a peak and a trough meet, they cancel each other out. This creates an interference pattern on the detector of bright and dark stripes.
In the new experiment the time slits change the frequency of light, which alters its colour. This created colours of light that interfere with each other, enhancing and cancelling out certain colours to produce an interference-type pattern.
The material used by the team was a thin film of indium-tin-oxide. The material had its reflectance changed by lasers on ultrafast timescales, creating the ‘slits’ for light.
The material responded much quicker to the laser control than expected, varying its reflectivity in a few femtoseconds. Such fine time control could create new technologies and even analogues for studying phenomena like black holes.