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Control of the Structure of Light at the Nanoscale

Final Report Summary - CONSTANS (Control of the Structure of Light at the Nanoscale)

The CONSTANS program has explored the ultimate limits of nanoscale light control. The program has demonstrated that infinitely small optical entities called optical singularities can be exploited to actively manipulate light and its interactions with matter at the smallest possible scale.
In the first half of the program optical singularities were investigated in the static situation. Several different nanophotonic structures both dielectric and metallic were evaluated to ascertain their usefulness for manipulating optical singularities. The behavior of the optical singularities was studied in detail. Through experiment, theory and simulations we found that various strategies for creating optical singularities with nanostructures are viable. Moreover, we determined that both photonic crystal waveguides and plasmonic nanowires are promising routes for enhancing the required nonlinear optical interactions. We demonstrated that the visualization of the actual light fields at the nanoscale not only showed beautiful and intriguing light patterns, but was also instrumental in explaining the underlying science.
One of the crucial properties of light that played an ever increasing role in the project was that of topology. It specifies a characteristic of light that may not change if small changes are made to the system. One such topological property was that of the topological charge of the optical singularities. We showed how it affects their distribution in space, but it also yielded a tragic love story: as the topological charge of the system cannot change singularities cannot just appear out of nowhere, they appear in pairs of opposite charge so that the total charge of the system stays constant, the also die/annihilate in similar pairs; the latter the can do with their birth partner –life-long fidelity- or with a random singularity of opposite charge -promiscuity-; the promiscuous singularities live longer. We also used topology as a means to transport light. Borrowing concepts from solid state physics we constructed photonic crystals that when put in contact, would produce optical states that could only travel in one direction given by the pseudospin of the light. Combining such phenomena we coupled the spin of light to the spin of matter to create a one-to-one relation between the spin of an excited quantum state and the direction in which a photon is emitted when that state returns to the ground state. This breakthrough can impact both quantum optics and help reduce the energy consumption of the internet.