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I just came across this article where they are claiming that they have photographed light behaving both as a wave and a particle!

The paper has been published in Nature Communications and I read the abstract which says,

Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave–particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinduced near-field is imaged synchronously with its spatial interference pattern. This methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits.

They do not really talk about photographing light but instead they seem to talk about Surface plasmon polaritons. The Wikipedia article says that the "polariton" is a quasiparticle. However, they still claim to have photographed light behaving both as a wave and a particle.

Is this a valid interpretation of the experiment?

noir1993
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  • Light wave is a probability wave because it assigns probability at each point in space at a certain time of detecting particle. Neither the wave carries particle nor the particle becomes wave. So, they can't simultaneously exist. They are just two incomplete pictures of the entity "light". Light wave is the probability wave that transports energy & momentum & not particle but of course, probability of detecting particle. . . –  Mar 02 '15 at 16:27
  • Yes, that is consistent with what I have read. – noir1993 Mar 02 '15 at 16:29
  • . . .I'll reiterate that light wave assigns probability at points at a certain time. Particles only apper when light interact with other body. When a particle is localized, which means we have a greater probability of finding the particle at a certain point, we are actually narrowing the probability wave group. So, when we actually detect the particle, there is no need of any probability! As Arthur Beiser remarks: There is a big difference between the probability of an event & the event itself. –  Mar 02 '15 at 16:35
  • Concerning wave-particle dualism I gave this description for photons in vacuum. In particular, there are no flying particles. – Moonraker Mar 02 '15 at 17:53
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    Quantum objects are neither particles nor waves, though they carry properties of both. I really don't understand why everyone insists on these weird "duality" statements when this idea has been laid to rest for decades now. – ACuriousMind Mar 03 '15 at 17:45
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    @ACuriousMind: Because a) people study quantum mechanics from the history books and historical books, even at many/most universities and b) the two concepts of "wave" and "particle" are "intuitive" (i.e. classical) and therefore people like to fall back on them... – Martin Mar 04 '15 at 09:51
  • Yes! See the 14 Mar 1013 article below. The classic Feynman double slit experiment answers your question: http://www.livescience.com/27881-feynman-double-slit-experiment-performed.html – Len Apr 25 '15 at 08:05

2 Answers2

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What they actually measured was not particle behavior. It was just a quantized energy transfer to the probing electrons. That corresponds to the absorption of individual photons, but it doesn't mean the Surface Plasmon Polariton (SPP) field was acting as a particle. It just interacted locally with the electron, as it must. Typically particle-like behavior happens when decoherence happens. In the two slit experiment, a superposition of a photon hitting the screen in two separate places is dynamically unstable and will decohere. Consequently, we only observe a single flash at a single point. Nothing like this happened in their experiment. They set up a standing wave in their SPP, and tossed electrons to image the interference fringes. If any interaction is to happen, it will happen at the electron's position, and if any decoherence is to take place in order to secure particle-like behavior, it will happen when the electron is detected. The SPP itself never acts like a particle -- it just acts like a quantum object, which, of course, it is. This paper would be much improved without mentions of confusing notions of wave particle duality. They have cool results as it is; anything else is spurious.

Here is a very good article explaining what it actually is, thereby clarifying the paper's findings.

Janus Boffin
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My answer to the question is first a question. How do you photograph a photon? You can measure a photon by detecting it's presence on photographic film, or by using some sort of photomultiplier and digital detector, or by a handful of other ways. My point is that these all require the photon to be absorbed by the detector, thus they must be localized, and therefor they are behaving as particles (as far our the image that results is concerned).

I suppose there are ways to indirectly image a photon, much as all photograph of non-photon objects is done, where we measure the photons that scatter off the surface of things. Possibly you could scatter light off of light, but again, to do that would be to "observe" light, to localize it, and it would once again lose any waviness to it and appear as a particle.

Anyways, if you can figure out how to take photographs of photons with out using any part of the electromagnetic field, maybe you can take pictures of wavicles. That would be worth a Noble or two. Of course, you are going to need pretty fast shutters, probably easier to just slow down the light.

Kebil Friesen
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