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Tuesday, March 3, 2015

Cool Science: Light as a particle and a wave

Sou | 3:44 PM Go to the first of 5 comments. Add a comment

Do you want to see light as both a particle and a wave? Didn't think you could?

Well, now you can, thanks to Fabrizio Carbone and his colleagues. Here it is:

Source: EPFL via

From EPFL:
A research team led by Fabrizio Carbone at EPFL has now carried out an experiment with a clever twist: using electrons to image light. The researchers have captured, for the first time ever, a single snapshot of light behaving simultaneously as both a wave and a stream of particles particle.
The experiment is set up like this: 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 traveling 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.
This is where the experiment’s trick comes in: The scientists 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 now visualize 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. As mentioned above, 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.
“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” says Fabrizio Carbone. In addition, the importance of this pioneering work can extend beyond fundamental science and to future technologies. 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.” 

Read the full article at EPFL.


L Piazza, T.T.A. Lummen, E Quiñonez, Y Murooka, B.W. Reed, B Barwick  & F Carbone. Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field. Nature Communications 6, Article number: 6407 doi:10.1038/ncomms7407


  1. Now all they need to do is rig that sucker up to an interferometer and see if they can catch the wave function collapsing.

  2. So smart yet they still use effing rainbow pallete to present their results! Sigh. See Ed Hawkins blog as to why this shouldn't be happening.

    R The Anon. (who is forced to use rainbow in his job)

    1. err palette. Colour me stupid...

      R. (somewhere over the rainbow)

  3. that reminds me of the heated debates I got with some friends when we were students : they were defending the ondulatory nature of particles totth and nails, while I was basically saying you cannot define it with macroscopic analogies but only characterize its behaviour. Of course, since we were students it ended in the tv room of the dorm with a Godfrey Ho movie ...
    I have dropped quantum mechanics for geophysics, but it's nice to see that kind of experiment trying to tackle with the mere nature of quantum mechanics. And for the first commenter, I *think* I've seen an experiment on collapsing functions - unless it was on quantic entanglement, I don't remember.

  4. From my old days in the EM laboratory involved with electron diffraction and imaging my faltering memory gives me a bit of insight what is going on. I am not absolutely sure but here is my take on this.
    If the wire was not energised by the laser the electron beam in the EM microscope would show classic Fresnel fringes either side of the wire. This shows the wave nature of the electrons in the EM beam interacting with the electric field of the nuclei in the wire to produce elastic scattering of the electrons. Elastic scattering means that there is no loss or gain of energy by any electrons in the EM beam.
    What is interesting is that there is quantum exchange of energy between the electrons in the beam and the standing wave plasmons in the wire when the laser is turned on. This causes the Fresnel fringe intensities to be modulated by the standing waves in the wire.
    I am assuming that this is a time averaged image even though the delta t is very small.
    I would have to read the original paper to get it clear in my mind. Very interesting work. Bert


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