02/07/2026 | Press Release from TU Berlin
Optical quantum chips are considered key components of future communications and computing technologies. However, their production has proven a complex process up to now due to the fact that the sources of individual light particles – known as semiconductor quantum dots – formed randomly on the chip and had to be located first using a complex and time-consuming process. Researchers at Technische Universität Berlin have now developed a solution to this problem: By carefully integrating "stressors" into the substrate, they can generate surface tension in such a way that artificial atoms in the form of semiconductor quantum dots grow precisely where desired. In doing so, they are laying the groundwork for scalable, industry-compatible manufacturing of optical quantum chips.
The research was conducted under the direction of Professor Stephan Reitzenstein at the Chair of Optoelectronics and Quantum Devices at TU Berlin's Institute of Physics and Astronomy, in collaboration with researchers from Carl von Ossietzky University Oldenburg. Together, they developed a new quantum chip architecture in which quantum dots, nanoscale semiconductor structures used to generate individual photons, are precisely integrated into the chip at specified locations. The results were published in the journal Light: Science & Applications.
From randomness to targeted fabrication
Quantum dots are considered promising sources of individual particles of light (photons). Such light particles are a key foundation for future applications such as secure quantum communication, quantum networks, quantum sensing, and photonic quantum computers. So far, however, a major problem has arisen during fabrication, with the quantum dots forming randomly on the semiconductor material during the growth process. As a result, researchers had to go to great lengths to identify suitable quantum dots before they could produce the necessary photonic structures around them. "For individual demonstrators, this approach was very successful. However, if you want to fabricate a lot of quantum light sources of comparable quality on a single chip, the random positioning of the quantum dots becomes a major obstacle," explains Kartik Gaur, who developed the quantum devices as part of his doctoral thesis. "Our approach moves this step to the crystal growth stage so that the quantum dots are created right where they will be needed in the photonic device."
Professor Reitzenstein's research group set about developing a method that determines the position of the quantum dots during the crystal growth process. This is made possible by a special layer hidden within the chip's substrate, which generates very precise material stresses and thus precisely controls the growth of the quantum dots. The quantum dots are then integrated directly into nanophotonic resonators, which collect the generated light particularly efficiently and make it available for quantum technology applications.
Professor Dr. Reitzenstein standing in front of the sample chamber of the electron beam lithography system, which is used to produce high-precision nanostructures for scalable next-generation quantum light sources.
High yield and consistent quality
Using the new method, the researchers fabricated a 6x6 array of 36 quantum light sources, in which all of the fabricated devices were functional. In doing so, they achieved excellent reproducibility, something which has rarely been achieved to date in semiconductor-based quantum photonics. "The real significance of this work doesn't only lie in the high yield of the devices," says Reitzenstein. "Most important is that we can demonstrate how high-performance quantum light sources can be realized on a semiconductor chip with controllable quality and high reproducibility. In doing so, we are addressing a key challenge in quantum photonics – namely the transition from individually optimized laboratory demonstrators to scalable, technologically viable platforms for future quantum systems."
Foundations for the next generation of quantum chips
In addition, the research team conducted a detailed investigation into how even the smallest deviations in the positioning of the quantum dots affect the performance of the devices. To do this, they combined various imaging, spectroscopic, and quantum-optical measurement techniques with numerical simulations. The theoretical work was carried out by Professor Christopher Gies's research group at Carl von Ossietzky University of Oldenburg. The models explain how the exact position of the quantum dots affects the properties of the light particles generated, and provide important guidelines for the development of future quantum chips.
High quality of quantum light sources successfully demonstrated
The team was also able to quantitatively demonstrate the performance of the quantum light sources. With the best devices, the researchers were able to extract nearly half of the generated light particles from the chip for further use, which represents a very good result. At the same time, the quantum mechanical "purity" of the individual light particles was over 99 percent. In addition, the light particles generated exhibited nearly identical quantum-optical properties. This is an important prerequisite for future photonic quantum computers and quantum networks, as these systems require that many photons interact with one another in exactly the same way.
Further information:
Scalable Quantum Photonic Platform Based on Site-Controlled Quantum Dots Coupled to Circular Bragg Grating Resonators, Kartik Gaur, Avijit Barua, Sarthak Tripathi, Léo J. Roche, Steffen Wilksen, Alexander Steinhoff, Sam Baraz, Neha Nitin, Chirag C. Palekar, Aris Koulas-Simos, Imad Limame, Priyabrata Mudi, Sven Rodt, Christopher Gies & Stephan Reitzenstein
https://www.nature.com/articles/s41377-026-02343-0
Author: Wolfgang Richter
Further information is available from:
Professor Dr. Stephan Reitzenstein
Chair of Optoelectronics and Quantum Devices
Institute of Physics and Astronomy
Faculty II – Mathematics and Natural Sciences
Technische Universität Berlin
Phone: +49 30 314-79704
Email: stephan.reitzenstein(at)tu-berlin.de