Quantum Shuttle to Quantum Processor Made in Germany

Germany has long been among the world leaders in the race to develop a quantum computer. As part of the BMBF-funded QUASAR project, top-class research institutions, universities and companies now aim to jointly apply the results into practice. The goal is a semiconductor quantum processor made in Germany that is based on the "shuttling" of electrons and is to be achieved with technology available in Germany. Project coordinator is Prof. Hendrik Bluhm, director at the JARA Institute for Quantum Information.

Quantum computers have the potential to outperform conventional supercomputers by far in certain problems, for example when it comes to controlling traffic flows in metropolitan areas or simulating materials at the atomic level. But it is still unclear which approach will win the race among quantum computers. Experiments with superconducting qubits, the smallest units of a quantum computer, are currently the most advanced. For example, Google’s quantum chips and the experimental quantum computer in the European Quantum Flagship project, which is to go into operation this year at Forschungszentrum Jülich, are based on them. But when it comes to large numbers of qubits, semiconductor qubits may have the advantage.

"At Jülich, we are investigating both types of qubits, semiconductor-based and superconductor-based. There are strong synergy effects, for example, in the development of quantum software, component development and their integration into experimental computer architectures," says Prof. Wolfgang Marquardt, Chairman of the Board of Directors of Forschungszentrum Jülich. "In the long term, we want to realize a freely accessible quantum computer for science at Jülich. The QUASAR project is an important step for this project – in combination with our other activities, such as the European Quantum Flagship or the research of quantum materials."

Silicon electron spin qubits are one promising system for semiconductor qubits because they have comparatively robust quantum properties and are much smaller in size than superconducting quantum bits. "A big advantage is that their production is largely compatible with the production of silicon processors. This means that, in principle, there is already a lot of experience with the fabrication processes," says project coordinator Professor Hendrik Bluhm, Director at the JARA Institute for Quantum Information. One example is Infineon in Dresden: in the project, the German semiconductor manufacturer helps with its production expertise adapting the component design for industrial manufacturing.

"Fundamental questions still need to be clarified. So far, it has not been possible to scale up quantum chips as easily as conventional computer chips. One problem has been geometric constraints. The qubits usually have to be very close together in order for them to be coupled to each other. Therefore, semiconductor qubits have been demonstrated up to now primarily in components that have no more than two coupled qubits close to each other. For a scalable architecture, however, we need more space on the quantum chip, for example for feed lines and control electronics," says Hendrik Bluhm.

In order to increase the distances, the researchers from the JARA cooperation of Forschungszentrum Jülich and RWTH Aachen University, together with other research partners, have developed a something called a quantum bus. This special interconnection element allows distances of up to 10 micrometres between the individual qubits to be bridged efficiently. In silicon qubits, the quantum information is encoded by the spin of electrons located in quantum dots – special nanoscopic semiconductor structures. The quantum bus can capture the electrons on these quantum dots and transport them in a controlled way without losing the quantum information.

A press release from Forschungszentrum Jülich. Further information on the QUASAR project and other projects in the field of quantum information and computing is available on the website of Forschungszentrum Jülich.