For the first time ever, scientists have photographed light behaving simultaneously as both a particle and a wave.
The photograph, above, is a momentous achievement, providing direct observation of both behaviours simultaneously for the first time, after decades of attempts by the scientific community. Previous research projects have successfully observed wave-like behaviours and particle-like behaviours in light, but not at the same time.
The dual behaviour of light, which is demonstrated through quantum mechanics and was first proposed by Albert Einstein, was only possible to capture by scientists at École polytechnique fédérale de Lausanne (EPFL), Switzerland, due to an unorthodox imaging technique.
The scientists generated the image with electrons, making use of EPFL’s ultrafast energy-filtered transmission electron microscope. This gave them a rare advantage over other institutions, as EPFL has one of only two such microscopes in the world.
The image was achieved first by firing a pulse of laser light at a miniscule metallic nanowire, adding energy to charged particles in the nanowire and making them vibrate.
The light waves travel along the nanowire in opposite directions, like lanes of cars on a road, but when they meet from opposite directions they form a new wave then appears as if it is “standing in place”, effectively confined to the nanowire.
This wave, which radiates around the nanowire, was the light source that was imaged.
The scientists fired a stream of electrons in close proximity to the nanowire, and imaged their interaction with this “standing wave”. As they came into contact with the light, their changes in behaviour acted as a visualisation of the light’s behaviour.
The electrons that interacted with the light, or photons, either slowed down or sped up, together forming a visualisation of the light’s wave.
However, the changes in speed also appeared as an exchange of quanta – packets of energy – between the electrons and the photons. These packets were the tell-tale sign of the light behaving as a particle.
The experiment is a significant step for future quantum mechanics research.
“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” said research leader Fabrizio Carbone.
However, the research could also be important for the future development of quantum-based technology.
“Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing,” he added.
The research, which was a collaborative effort between EPFL, Trinity College and the Lawrence Livermore National Laboratory, is published today in the journal Nature Communications.
Image courtesy of Fabrizio Carbone/EPFL.
Journal Reference: Piazza L, Lummen TTA, Quiñonez E, Murooka Y, Reed BW, Barwick B, Carbone F. Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field. Nature Communications 02 March 2015. DOI: 10.1038/ncomms7407