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?
Answer
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.
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