In a breakthrough, Swiss scientists have succeeded in taking the first ever photograph of light behaving both as a wave and as a particle.
Even though a variety of experiments have successfully observed both the particle- and wave-like behaviours of light, they have never been able to observe both at the same time.
Taking a radically different experimental approach, scientists at Swiss Federal Institute of Technology in Lausanne (EPFL) have now been able to take the first ever snapshot of light behaving both as a wave and as a particle.
The research team led by Fabrizio Carbone at EPFL carried out an experiment using electrons to image light.
In the experiment a pulse of laser light is fired at a tiny metallic nanowire. The laser adds energy to the charged particles in the nanowire, causing them to vibrate.
Light travels along this tiny wire in two possible directions, like cars on a highway. When waves travelling in opposite directions meet each other they form a new wave that looks like it is standing in place.
Here, this standing wave becomes the source of light for the experiment, radiating around the nanowire.
The scientists then shot a stream of electrons close to the nanowire, using them to image the standing wave of light. As the electrons interacted with the confined light on the nanowire, they either sped up or slowed down.
Using the ultrafast microscope to image the position where this change in speed occurred, Carbone’s team could visualise the standing wave, which acts as a fingerprint of the wave-nature of light.
While this phenomenon shows the wave-like nature of light, it simultaneously demonstrated its particle aspect as well.
As the electrons pass close to the standing wave of light, they “hit” the light’s particles, the photons.
This affects their speed, making them move faster or slower. This change in speed appears as an exchange of energy “packets” (quanta) between electrons and photons.
The very occurrence of these energy packets shows that the light on the nanowire behaves as a particle, researchers said.
“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” said Carbone.
“Being able to image and control quantum phenomena at the nanometre scale like this opens up a new route towards quantum computing,” Carbone said.
The work is published in Nature Communications.