Professor Stephan Reitzenstein 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.
Felix Noah
Imagine having to build a state-of-the-art smartphone with key components randomly appearing somewhere on the circuit board. You would have to laboriously search for every single part and plan the rest of the electronics around it. What sounds like a logistical nightmare was, until recently, the bitter reality of quantum technology. Or as John Martinis, Nobel Prize winner for Physics 2025, recently put it: “We are currently still building qubits in an almost hand-crafted way.”
But scientists at the TU Berlin now seem to have achieved a breakthrough. It could pave the way for the mass production of quantum chips. Until now, the production of optical quantum chips – the heart of future quantum computers and tap-proof communications – has been a laborious process.
No more chance
The required light sources, so-called semiconductor quantum dots, were previously created purely by chance on the chip during growth. Researchers first had to spend a lot of time localizing these artificial atoms before they could manufacture the nanophotonic structures for light guidance precisely around them. “This approach was successful for individual laboratory experiments. But when it came to producing many comparable light sources on one chip, the random position became the central bottleneck,” explains Kartik Gaur, who developed the new components as part of his doctoral thesis.
The team led by Professor Stephan Reitzenstein at the TU succeeded – in cooperation with the University of Oldenburg – in developing an architecture that leaves no chance for chance. The highlight of the method lies deep inside the chip: a special, hidden layer creates precise material tensions, so-called stressors, on the surface.
36 out of 36 hits
These tensions act like a blueprint for nature. This means that the quantum dots grow exactly in the places where they will later be needed for the finished component. They are then immediately integrated into nanophotonic resonators, which capture the light generated with the highest efficiency.
The researchers demonstrated how precise the new process is with a 6×6 grid made up of 36 quantum light sources. All 36 components were fully functional. This 100 percent yield and reproducibility marks a crucial step away from individually optimized one-off pieces towards scalable, industry-compatible platforms.
Experts are of the opinion that the TU Berlin has thus addressed one of the biggest hurdles in quantum photonics: the transition from laboratory experiments to technologically usable applications. The vision of powerful quantum computers and absolutely secure communication networks has now become a lot more tangible.
