Light confined on a nanowire, behaving as both particle and wave.An innovative experimental technique by a team from the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland has helped produce the first image of light behaving simultaneously as a particle and a wave. The approach allows for the control and visualization of plasmonic fields at the nanoscale, offering potential for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits, as well as potential benefits in optical data storage devices and biosensing applications.
Although previous studies have demonstrated light as either a wave or a particle, this was at different times – no experiment has managed to photograph light behaving simultaneously as both a wave and a stream of particles, despite quantum mechanics showing that light can show both natures at the same time.
The experiment, as reported in Nature Communications [Piazza et al. Nat. Commun. (2015) DOI: 10.1038/ncomms7407], used a pulse of laser light fired at a metallic nanowire, which added energy to the charged particles in the nanowire, resulting in it vibrating. The light can move along the wire in either direction; when waves traveling in opposite directions meet each other, they form a new wave that appears to not be moving. This standing wave then becomes the source of light for the experiment, radiating around the nanowire.
At this point, the team fired a stream of electrons close to the nanowire, using them to image the standing wave of light. As the electrons pass near to and interact with the light, they collide with the light's particles, the photons, changing their speed. Ultrafast microscopy was used to image the position at which this change in speed took place, and visualize the standing wave. The change in speed resembles an exchange of energy “packets” (quanta) between the electrons and photons, proving the light on the nanowire is behaving as a particle. As team leader Fabrizio Carbone said, “This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly.”
The researchers are continuing their measurements to expose other aspects of the complementarity principle, and investigate their implications for circuits that exploit confined electromagnetic fields for quantum devices. They are also investigating developing and characterizing photonics circuits using the same methodology. As Carbone explains, “Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing.”