The Quantum Bus: Shuttling Electrons, Laying Foundation for Industrial Production of Quantum Processors

Quantum Shuttle to Quantum Processor Made in Germany Launched

The quantum computer race is in full swing. Germany has long been one of the world leaders in basic research. An alliance between Forschungszentrum Jülich and the semiconductor manufacturer Infinion, together with institutes of the Fraunhofer-Gesellschaft (IAF, IPMS) as well as the Leibniz Association (IHP, IKZ), the universities of Regensburg and Konstanz and the quantum startup HQS, now aims to apply the results to industrial production. 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. The QUASAR project, which is funded with over 7.5 million euros by the Federal Ministry of Education and Research (BMBF), aims to lay the foundations for the industrial production of quantum processors over the next four years.

Halbleiter-Quantenchip der JARA-Kooperation des Forschungszentrum Jülich und der RWTH AachenSemiconductor quantum chip from the JARA cooperation between Forschungszentrum Jülich and RWTH Aachen University
Copyright: Jülich Aachen Research Alliance (JARA)

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 at Forschungszentrum Jülich. 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.

Arbeitsgruppe Prof. Dr. Hendrik BluhmProject coordinator Prof. Dr Hendrik Bluhm (2nd from left) at the JARA Institute for Quantum Information
Copyright: Simon Wegener

“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.

From the laboratory to production

The exchange of electrons is also known as “shuttling”. In the laboratory, experimental samples are already showing promising results. Now the Jülich researchers want to adapt the device’s design to industrial manufacturing processes. To this end, they have joined forces in the QUASAR project with Infineon Dresden, the start-up HQS specialising in quantum mechanical material simulations, institutes of the Fraunhofer-Gesellschaft (IAF, IPMS) as well as the Leibniz Association (IHP, IKZ) and the universities in Regensburg and Konstanz.

Quantum Shuttle

The quantum bus (QuBus) makes it possible to transport individual electrons together with their quantum information over distances of up to 10 micrometres. The technology is based on electrodes connected in series, which use pulsating voltages to move the quantum dots from one end to the other as if on a conveyor belt.

Elektronenmikroskopische Aufnahme eines 10 Mikrometer langen Quantenbusses.

Electron microscope image of a quantum bus (Copyright: RWTH Aachen / Inga Seidler)

 “One of the challenges here is the required degree of material quality, which is much higher for this application than for the production of conventional computer chips,” says Hendrik Bluhm. “Another open point is the miniaturisation of the control systems on the chip. In principle, however, we see great potential in this approach for complex circuits. Millions of qubits are realistic.”

The QUASAR project will run until January 2025. The next step is to build a demonstrator with around 25 coupled qubits, which will be implemented in a follow-up project and integrated into the modular HPC environment of the Jülich Supercomputing Centre via the “Jülich User Infrastructure for Quantum Computing” (JUNIQ) with cloud access.

Other quantum projects launched

In addition to the QUASAR project, Forschungszentrum Jülich is participating in other quantum technology projects that have been launched in recent weeks and months. In the new QLSI project of the European Quantum Flagship, which started in September 2020, Forschungszentrum Jülich, together with partners from the QUASAR project and other European institutions, is developing an industry-compatible technology for semiconductor qubits as a complement to QUASAR, which will be explored by a demonstrator with 16 quantum dots. The QLSI project is coordinated by the French research institute CEA-Leti, with Infineon, the Fraunhofer institutes IAF and IPMS as well as the Leibniz Institute for Innovative Microelectronics and the University of Konstanz also involved in the project.
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Together with other German research institutions and universities as well as Infineon, Forschungszentrum Jülich is involved in the GeQCoS joint project to develop an improved quantum processor based on superconducting qubits. The project, funded by the BMBF with 14.5 million euros, started in February 2021 and is coordinated by the Walther-Meißner-Institute of the Bavarian Academy of Sciences and Humanities. Other partners in the project include the Karlsruhe Institute of Technology, the Friedrich-Alexander-Universität Erlangen-Nürnberg, the Technical University of Munich and the Fraunhofer Institute for Applied Solid State Physics.
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The DAQC joint project brings start-ups and companies together with research institutions and computing centres. The goal is the production and operation of a digital-analogue quantum computer, as well as the development of the associated calibration and control technology. The project, funded by the BMBF with 12.4 million euros, also started in February 2021 and is coordinated by the quantum start-up IQM Germany GmbH. In addition to Forschungszentrum Jülich, Infineon and the startup Parity Quantum Computers from Austria, as well as the Leibniz Supercomputing Centre and Freie Universität Berlin are also involved in the project.
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Profiles of the project partners in the QUASAR joint project

(“Semiconductor QUAntum processor with Shuttling-based Scalable ARchitecture”)

HQS Quantum Simulations GmbH is a KIT spin-off with 18 employees and focuses on quantum mechanical material simulations. HQS cooperates with companies such as BASF, BOSCH and Merck in the fields of materials science and chemistry.

The Fraunhofer Institute for Applied Solid State Physics IAF develops hardware for quantum technology and electronic systems. Its core competencies range from materials research, design and technology development and (cryogenic) measurement technology to circuits and systems.

Innovations for High Performance Microelectronics / Leibniz-Institut für Innovative Mikroelektronik (IHP) conducts research and development on silicon-based high-frequency circuits and technologies, including new materials. It also offers prototype production via its 200 mm production line.

The Leibniz Institute for Crystal Growth (IKZ) specialises in the growth of solid crystals, epitaxial thin films and nanostructures. Its development and characterisation of isotopically pure 28Si crystals is of particular note.

Infineon Technologies Dresden GmbH & Co. KG is considered one of the most modern and largest semiconductor development and production sites in Germany with around 2,700 employees. Infineon Dresden has two highly automated production lines covering around 50 different technologies. The Infineon group is strategically involved in post-quantum cryptography as well as different quantum hardware concepts such as ion traps, superconductors and approaches based on SiGe quantum wells, the latter of which are being investigated at their Dresden location.

Fraunhofer IPMS-CNT works on innovative components and technologies with the aim of integrating them into CMOS platforms. It has more than 40 industry-standard processing facilities and makes use of comprehensive analytics, while also having a close connection to the production lines of industrial project partners.

The JARA Institute for Quantum Information (JARA) is located at Forschungszentrum Jülich and RWTH Aachen University. The research group led by Prof. Hendrik Bluhm and Dr. Lars Schreiber has many years of experience in the fabrication, coherent manipulation and modelling of semiconductor qubits. One of the research focuses is on their scalability.

The Chair of Condensed Matter Theory and Quantum Information at the University of Konstanz, held by Prof. Guido Burkard, has a long history of research in quantum computing in solid-state systems, especially spins in semiconductors and two-dimensional materials.

The “Epitaxial Nanostructures” group of Prof. Dominique Bougeard at the University of Regensburg researches quantum effects in semiconductor nanostructures. The focus is on molecular beam epitaxy of 28Si/SiGe heterostructures and quantum transport for spin qubits.

Funding of QUASAR project

Funding organisation: Federal Ministry of Education and Research (BMBF)
Funding programme: Quantentechnologien – von den Grundlagen zum Markt
Funding reference no. of Forschungszentrum Jülich: 13N15652

Halbleiter-Quantenchip der JARA-Kooperation des Forschungszentrum Jülich und der RWTH Aachen

Semiconductor quantum chip from the JARA cooperation between Forschungszentrum Jülich and RWTH Aachen University
Copyright: Jülich Aachen Research Alliance (JARA)

Further information:

Press release, Infineon, 24 February 2021

Dossier: Quantum Technology

JARA Institute for Quantum Information

Image usage: The images contained in this press release may be used for context-related media coverage, provided credit is given, unless otherwise stated.


Prof. Dr. Hendrik Bluhm (project coordination)
Head of the JARA Institute for Quantum Information (PGI-11)
Forschungszentrum Jülich
Phone: +49 241 80-27110
E-mail: [email protected]

Press contact:

Tobias Schlößer
Corporate Communications
Forschungszentrum Jülich
Phone: +49 2461 61-4771
E-mail: [email protected]

Source:  Julich Forschungszentrum.  Prof. Dr. Hendrik Bluhm,  Quantum Shuttle to Quantum Processor Made in Germany Launched…

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