Quantum computers are making headlines... but what's behind the hype? With this question in mind, Daniela Zahn, group leader for electronics and quantum component testing at Fraunhofer EMFT, took the audience on a journey into the tiny, ice-cold world of superconducting quantum computers. She gave a highly accessible introduction to the quantum mechanical fundamentals of quantum computers – What are qubits? How can their special abilities for superposition and entanglement be exploited for this very different type of computing? – and talked about the areas of application in which quantum computers are expected to offer advantages. However, the young scientist also addressed the many challenges that she and many other scientists have to overcome in their daily research on the way to large-scale systems.
One of these challenges is connecting the qubits. Each qubit on a superconducting quantum chip is controlled by at least one link and read out by a second link. As long as the number of qubits is in the double-digit or low triple-digit range, this can be achieved with the coaxial cables used to date. However, if the number of qubits rises to a level that will eventually be necessary for practical applications – tens of thousands to millions of qubits – the space required for cabling with the control and readout electronics also increases enormously. One solution that Fraunhofer EMFT is therefore working on is extremely thin, superconducting cables that enable a high density of signal connections in a very small space. However, these connections must also meet high requirements in terms of thermal stress, for example, because frosty temperatures of only a few millikelvin are essential for the operation of a superconducting quantum computer. Elias Meltzer, one of the scientists involved in the development of these foil-based superconducting cables, spoke about this complexity and the technical challenges involved in manufacturing them. The audience's keen interest and in-depth knowledge were evident in the many detailed questions that were already asked during the presentation.
There was time for even more questions after the presentations, when visitors had the opportunity to visit various laboratories at Fraunhofer EMFT in small groups. From the antechamber, they were able to look into the clean room where the flexible connections are manufactured. There was not enough time for all participants of the well-attended event to change into the protective clothing required to enter the clean room, but the machines were clearly visible through the large windows. Martijn Goedbloed, who is also involved in the development of the special cables, showed the various stages of production – films that are coated with more and more materials and finally given their structure using a lithographic process – right through to the finished, gold-coated cable with connection points.
Daniela Zahn demonstrated where and how this connection is then used in the cryo lab on a small dilution refrigerator. One of the larger cryostats in her lab was busy performing a measurement, hidden behind a cover that shields the system from environmental influences, especially room temperature. The characteristic hissing and whistling of the helium pumps used for cooling created an authentic laboratory atmosphere. When asked about this, Daniela Zahn laughs – she says she hasn't noticed the noise for a long time.
More information:
All other events in the “MQV-Einblicke” series, with links to registration, can be found here: https://www.munich-quantum-valley.de/quantum-2025/mqv-einblicke
An overview of all further events organized by the MQV and its partners to mark the International Year of Quantum can be found here: https://www.munich-quantum-valley.de/quantum-2025