Photons Sense Each Other

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COPENHAGEN, Denmark, Dec. 28, 2012 — Photons can “sense” each other and coordinate their separate paths through a complex material, new research from the Niels Bohr Institute shows.

The scientists demonstrated that photons emitted from a light source embedded in a complex and disordered structure can coordinate their travel through the medium as a result of their wave properties.

The illustration shows how the scattering of photons occurs in a complex photonic medium. Two photons are emitted from a light source in the center and move through a labyrinth to illustrate complex scattering. The photons take different paths through the medium, but they are interdependent in the sense that the chance of observing a photon at one outlet is increased if a photon is observed at the other outlet. Courtesy of David García, Niels Bohr Institute.

“We work with nanophotonic structures in order to control the emission and propagation of photons,” said David García, a postdoctoral quantum photonics researcher at the institute, which is part of the University of Copenhagen. “We have discovered in the meantime that inevitable inaccuracies in the structures lead to random scattering. As a consequence, the transport of photons follow a random path — like a drunken man staggering through the city’s labyrinthine streets after an evening in the pub.”

Continuing with the analogy, just because one drunken man gets home safely, it is not certain that a whole crowd of drunken people spreading out from the pub will also find their way safely through the city’s winding streets. There is no relationship between the different random travelers.

There is, however, when you are talking about photons.

David García works in the quantum photonics laboratory at the Niels Bohr Institute. He experiments with using nanophotonic structures to control the emission and propagation of photons. The research shows that photons can “sense” each other and coordinate their way through a complex material. Courtesy of Ola Jakup Joensen, Niels Bohr Institute.

To see how photons can sense each other and coordinate their travel through a material, the scientists inserted a small light source — in this case, a quantum dot — in a nanophotonic structure containing disorder in the form of a random collection of light-diffusing holes, García said.

“The photons are scattered in all directions and are thrown back and forth,” he said. “But photons are not just light particles; they are also waves, and waves interact with each other. This creates a link between the photons, and we can now demonstrate in our experiments that the photons’ path through the material is not independent from the other photons.”

Analyzing the photons’ path through the medium could provide valuable insight into microscopic complex structures.

“The method could be a new way to measure the spatial properties of complex disordered materials, like biological tissue, and since the light sources are very small, you will be able to place them without destroying the material, and you have the potential for very high spatial resolution,” García said.

The results were published in Physical Review Letters (doi: 10.1103/PhysRevLett.109.253902).  

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Published: December 2012
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
quantum dots
A quantum dot is a nanoscale semiconductor structure, typically composed of materials like cadmium selenide or indium arsenide, that exhibits unique quantum mechanical properties. These properties arise from the confinement of electrons within the dot, leading to discrete energy levels, or "quantization" of energy, similar to the behavior of individual atoms or molecules. Quantum dots have a size on the order of a few nanometers and can emit or absorb photons (light) with precise wavelengths,...
biological tissueBiophotonicsDavid GarcíaDenmarkdisordered materialsEuropeImagingnanoNiels Bohr Institutephoton sensingphotonicsphotonsquantum dotsResearch & TechnologyspectroscopyUniversity of Copenhagenwave properties

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