Researchers control individual quanta of light at very high speeds

A team of German and Spanish researchers from Valencia, Münster, Augsburg, Berlin and Munich managed to control individual light quanta with an extremely high degree of precision. In Nature Communication, the researchers report how, by means of a sound wave, they switch individual photons on a chip 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 communications. While glass fibers with laser light form the World Wide Web, nanoscale sound waves on chips process signals at gigahertz frequencies for wireless transmission between smartphones, tablets or laptops. One of the most pressing questions for the future is how these technologies can be extended to quantum systems, to build secure (i.e. eavesdropping) quantum communication networks.

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

Dr Mauricio de Lima, who does research at the University of Valencia and coordinates the work carried out there, adds: “We knew the principle of operation of our chip with regard to conventional laser light, but now, in using quanta of light, we have succeeded in making the much-desired breakthrough into quantum technologies.”

In their study, the researchers fabricated a chip equipped with tiny “conductive paths” for light quanta, called waveguides. They are about 30 times thinner than a human hair. In addition, this chip contained sources of quantum light, called quantum dots.

Dr Matthias Weiß from the University of Münster carried out the optical experiments and adds: “These quantum dots, only a few nanometers in size, are islands inside the waveguides that emit light under form individual photons. Quantum dots are embedded in our chip, so we don’t need to use complicated methods to generate individual photons using another source.”

Dr. Dominik Bühler, who designed the quantum chips as part of his Ph.D. at the University of Valencia, emphasizes the speed of the technology: “Using nanoscale sound waves, we are able to directly switch photons on the chip between two outputs at unprecedented speed as they propagate through waveguides.

The researchers see their results as an important step on the way to hybrid quantum technologies because they combine three different quantum systems: quantum light sources in the form of quantum dots, created light quanta, and phonons (the quantum particles in the ‘sound wave). The hybrid quantum chips – designed at the University of Valencia and fabricated at the Paul Drude Institute for Semiconductor 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 to improve our chip so that we can program the quantum state of photons as we wish, even control multiple photons of different colors between four or more outputs,” says Dr. Mauricio de Lima, with a view into the future.

Professor Hubert Krenner adds: “Here we benefit from a unique strength possessed by our sound waves at the nanometer scale: because these waves propagate virtually losslessly across the surface of the chip, we can precisely control almost as many waveguides as many waves as we want with a single wave – and with an extremely high degree of precision.”