HomeSciencePhysicsResearchers control individual light quanta at very high speed

Researchers control individual light quanta at very high speed

A focused laser beam (left, blue) generates single pictures through a single quantum dot in the photonic waveguides (red), fabricated on top of crystalline gallium arsenide (GaAs) aluminum gallium arsenide (Al0.2Ga0.8As). Two interdigitated electrodes (interdigital transducers, IDT) generate nanoscale sound waves (surface acoustic waves, SAWs), which dynamically load the waveguides. The nanoscale sound wave generated by the left IDT changes the color of the individual photons emitted. The two waveguides are coupled by two so-called multimode interference beam splitters (MMIs). The sound wave generated by the right IDT sorts the single photons according to their color (red and green) between the two outputs on the right. Credits: Dominik Buhler

A team of German and Spanish researchers from Valencia, Münster, Augsburg, Berlin and Munich has succeeded in controlling individual light quanta with extreme precision. In Nature communication, the researchers report how they use a sound wave to switch individual photons on a chip back and forth between two outputs at gigahertz frequencies. This method, demonstrated here for the first time, can now be used for acoustic quantum technologies or complex integrated photonic networks.

Light waves and sound waves form the technological backbone of modern communication. While fiber optics with laser light make up the World Wide Web, nanoscale sound waves on chips process signals at gigahertz frequencies for wireless transfer between smartphones, tablets or laptops. One of the most pressing questions for the future is how to expand these technologies quantum systemsto build secure (i.e. tap-free) quantum communication networks.

“Light quanta or photons play a very central role in the development of quantum technologies,” says physicist Prof. Hubert Krenner, who is leading the study in Münster and Augsburg. “Our team has now managed to generate individual photons on a thumbnail-sized chip and then drive it with unprecedented precision, precisely clocked by sound waves,” he says.

Dr. Mauricio de Lima, who conducts research at the University of Valencia and coordinates the work there, adds: “The functional principle of our chip was known to us with regard to conventional laser light, but now, with the help of light quanta, we have succeeded in making the long-desired breakthrough into quantum technologies.”

In their study, the researchers fabricated a chip equipped with minute “conducting paths” for light quanta – so-called waveguides. These are about 30 times thinner than a human hair. In addition, this chip contained quantum light sources, so-called quantum dots.

Dr. Matthias Weiß from the University of Münster performed the optical experiments and adds: “These quantum dots, only a few nanometers in size, are islands in the waveguides that emit light as individual photons. The quantum dots are contained in our chip, so we don’t need to using complicated methods to generate individual photons through a different source.”

Dr. Dominik Bühler, who designed the quantum chips as part of his Ph.D. at the University of Valencia, points out how fast the technology is: “By using nanoscale sound waves, we are able to directly switch the photons on the chip back and forth between two outputs while propagating in the waveguides with an unprecedented speed.”

The researchers consider their results a milestone on the road to hybrid quantum technologies, as they combine three different quantum systems: quantum light sources in the form of quantum dots, the created light quanta, and phonons (the quantum particles in the sound wave). The hybrid quantum chips – designed at the University of Valencia and fabricated by the Paul Drude Institute of Solid-State Electronics using quantum dots produced at the Technical University of Munich – exceeded the expectations of the research team.

The international team has taken another decisive step towards acoustic quantum technologies. “We are already working hard on improving our chip so that we can program the quantum state of the photons as we want, or even control multiple photons with different colors between four or more outputs,” says Dr. Mauricio de Lima, with a view to the future.

prof. Hubert Krenner adds: “We are taking advantage here of a unique power that our nanoscale sound waves have: Since these waves propagate almost losslessly on the surface of the chip, we can cleanly drive almost as many waveguides as we want with just a single wave – and with an extremely high degree of precision.”

More information:
Dominik D. Bühler et al, On-chip generation and dynamic piezo-optomechanical rotation of single photons, Nature communication (2022). DOI: 10.1038/s41467-022-34372-9

Offered by Westfälische Wilhelms-Universität Münster

Quote: Researchers control individual light quanta at very high speed (2022, Nov. 21) Retrieved Nov. 21, 2022 from

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