Light photographed as simultaneous wave and particle

This rendering shows light's behaviour as a wave (top) and particle EPFL

It has long been known that light can behave as a particle or a wave, but for the first time researchers at the Swiss Federal Institute of Technology Lausanne (EPFL) have managed to document light behaving as both simultaneously.

Using a tiny metal nanowire, the research team aimed a pulse of light at the wire, causing it to vibrate and resulting in a standing wave of light. The scientists then tried something new: they focused a stream of electrons near the wire, causing them to interact with the light travelling along it from the pulse.

During this interaction, the electrons sped up and slowed down as they hit the light on the wire. Using a highly sophisticated microscope, researchers were able to see and document not only the standing wave but also the electrons hitting the photons in the nanowire. This demonstrated the electrons’ and photons’ energy exchange, showing the light on the wire behaving as a particle while simultaneously producing a wave.

The laser aims both light particles and photons at the wire (centre), which creates both a particle interaction and a standing wave EPFL

The energy exchange between electrons and photons are known as “quanta” and serves as the backbone of quantum mechanics – physics at the level of subatomic particles, with applications ranging from understanding the composition of the universe to medical imaging and computing.

“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” said Fabrizio Carbone, the project’s lead researcher.

“Being able to image and control quantum phenomena at the nanometre scale like this opens up a new route towards quantum computing.”

The team’s results were published in the scientific journal Nature Communications.