This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Quantum communication promises many advantages over today's standard technologies, including absolutely secure transmission of large amounts of data. However, it requires single photons—and generating them is very difficult.
Researchers at the Technical University of Munich (TUM) and the Munich Center for Quantum Science and Technology (MCQST) have developed a new method that overcomes the problems of previous approaches. Instead of amplifying the desired frequency, the researchers selectively suppress unwanted frequencies. Until now, so-called resonators have mostly been used to produce single photons—tiny optical structures that influence photon sources, causing them to emit light predominantly at a specific frequency.
However, these resonators function only within a narrow frequency range and must be precisely tuned to the respective photon source. Researchers at TUM and MCQST have developed a new approach that takes the opposite route. Instead of causing emitters to emit more light at a specific frequency, they adapt the emitter's environment so that less light is emitted at unwanted frequencies.
To do this, they use photonic crystal waveguides. These nanostructures use regularly arranged patterns to block pathways through which a photon source can emit light. The team designs the photonic crystal waveguides to suppress only unwanted light frequencies while preserving the desired ones.
The research is published in the journal Nature Communications. Initial experiments confirm the technology's effectiveness: Using photonic crystal waveguides, the researchers were able to increase the proportion of desired photons in emitted light from about 23% to around 72%. This means the new method achieves results that were previously attainable only with significantly more complex resonator approaches.
With the new approach, photon generation also occurs slightly more slowly than before. This, too, is important for quantum communication: "If photons are generated too quickly, it's difficult for us to control their properties," explains Andreas Reiserer, professor of quantum networks at TUM. "Our approach is therefore significantly better suited for many emitters than the resonators used to date." The researchers conducted their initial experiments using erbium as the photon source—an element already used in fiber-optic technologies today.
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