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.