Scientists capture first ever image of light acting as a particle and a wave

Despite being a well-established tenet of modern physics, the particle-wave duality of light can be a real mind-bender. This approach to understanding the universe was pioneered by scientists like Albert Einstein and Max Planck, eventually leading to quantum mechanics. Researchers have been trying to visualize light in both forms ever since, but haven’t had success until now. A team at the Swiss Federal Institute of Technology in Lausanne (EPFL) claim they’ve devised an experiment to photograph light as both a particle and wave.

Einstein’s eureka moment in the study of light came when he described the photoelectric effect. When UV light hits a metal surface, it results in an emission of electrons. Einstein explained this phenomenon by proposing that light can act as a particle in addition to a wave. We now know these particles as photons, but that term wasn’t coined until later. Subsequent experiments have confirmed the dual property of light, but actually seeing both at once would be something. The EPFL team led by Fabrizio Carbone took that original experiment and turned it on its head to snap such a picture of light.

The experiment started with laser pulses being fired at a metallic nanowire. The laser excited the particles of the nanowire, causing energy to propagate back and forth down the length of the wire. This traps the light as a standing wave and serves as the source of light in the experiment. There are a variety of ways to observe this system and get a result that shows you light as a wave, but the EPFL researchers wanted to see the particle aspect at the same time. To resolve photons at the same time, they fired a stream of electrons at the wire and watched the resulting mishmash.

As the electrons pass the nanowire, some of them will interact with the photons in the standing wave. A highly sensitive microscope was used to observe the nanowire for evidence of electrons that sped up or slowed down from this interaction. So that’s the wave, but what about individual particles? This change in speed comes can be measured as an exchange of energy packets, or quanta. The microscope was used to map the locations where the energy packet exchange was taking place along the wire, leading to the image seen above — a depiction of light as a particle and a wave in the same system.

This direct observation of the quantum nature of light could affect things beyond the lab. Tracking the nuances of quantum mechanics on the small scale could prove invaluable to the development of quantum computing. The quantum universe is still bizarre and hard to fully grasp, but this could get us a little closer to understanding it.