A new technology for manipulating light

Quantum computers are one of the most important future technologies in the 21st centuryst century. Researchers from the University of Paderborn, led by Professor Thomas Zentgraf and in collaboration with colleagues from the Australian National University and the Singapore University of Technology and Design, have developed a new technology for manipulating light that can be used as a basis for future optical quantum computers. The results have just been published in the journal Nature photonics.

New optical elements for manipulating light will allow more advanced applications in modern information technologies, especially in quantum computers. But a major challenge that remains is the non-reciprocal propagation of light through nanostructured surfaces, where these surfaces have been manipulated on a small scale. Professor Thomas Zentgraf, head of the working group for ultra-fast nanophotonics at the University of Paderborn, explains: “In mutual propagation, light can take the same path back and forth through a structure; however, non-reciprocal prevalence can be compared to a one-way street. where it can only extend in one direction. Non-reciprocity is a special property of optics that causes light to produce different material properties when its direction is reversed. An example could be a glass window that is transparent on one side and lets light through, but acts as a mirror on the other side and reflects light. This is called duality. “In photonics, such duality can be very useful in developing innovative optical elements to manipulate light,” says Zentgraf.

In a current collaboration between his working group at the University of Paderborn and researchers from the Australian National University and the Singapore University of Technology and Design, non-reciprocal propagation of light has been combined with a conversion frequency of the laser light, i.e. a change in frequency and therefore also the color of the light. “We used frequency conversion in specially designed structures, with dimensions in the order of a few hundred nanometers, to convert infrared light – which is invisible to the human eye – into visible light,” explains Dr. Sergey Kruk, Marie Curie Fellow in Zentgraf group. Experiments show that this conversion process takes place in only one illumination direction of the nanostructured surface, while it is completely suppressed in the opposite illumination direction. This duplication of frequency conversion characteristics has been used to encode images to an otherwise transparent surface. “We arranged the different nanostructures in such a way that they produced a different image depending on whether the sample surface was illuminated from the front or back,” explains Zentgraf, adding: “The images only became visible when we used infrared laser light for illumination.”

In their first experiments, the intensity of frequency-converted light in the visible range was still very low. So the next step is to further improve the efficiency so that less infrared light is required for frequency conversion. In future optically integrated circuits, frequency conversion directional control could be used to directly switch light with other light or to produce specific photonic conditions for quantum optics calculations directly on a small chip. “Perhaps we will see an application in future optical quantum computers where the directed production of individual photons using frequency conversion will play an important role,” says Zentgraf.

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Materials supplied by University of Paderborn. Note: The content can be edited for style and length.

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