Understanding and utilizing atomic quantum effects

The first Junior Research Groups for Quantum Photonics have started work at the Carl-Zeiss-Stiftung Center for Quantum Photonics (CZS Center QPhoton), where three universities have been conducting joint research into new quantum technologies since 2022. They are headed by physicist Dr. Laëtitia Farinacci and physicist Dr. Stephan Welte respectively and are based at the University of Stuttgart. Stuttgart's strong quantum research offers both groups ideal conditions.

"Stuttgart provides a highly stimulating environment for my research in quantum technologies," says Farinacci. "And thanks to the collaboration within QPhoton, I have access to a network that works on closely related research topics." Welte also appreciates the ideal environment, stating, "There is a wealth of theoretical and experimental expertise available for my work here. In addition, the other QPhoton sites in Ulm and Jena, as well as the Center for Integrated Quantum Science and Technology  (IQST), located in Ulm and Stuttgart, represent an ideal research network."

Welte and Farinacci head the first two early career research groups at the Carl-Zeiss-Stiftung Center for Quantum Photonics (CZS Center QPhoton) in Stuttgart.  At the CZS Center QPhoton, scientists from three universities have been conducting cross-location research on innovation topics in quantum technology since 2022. The center is funded by the foundation Carl-Zeiss-Stiftung with 12 million euros. QPhoton now also offers outstanding young scientists the opportunity to set up independent research groups. A total of four early career research groups are being funded with a budget of up to EUR 700,000 over five years, two of them in Stuttgart.

The goal of Stephan Welte's CZS Junior Research Group, which is based at the 5th Institute of Physics at the University of Stuttgart, is to set up an experiment for information transmission in a quantum network. Welte uses atoms as qubits for this purpose. Qubits are the smallest units of information on which the function of quantum computers and quantum networks is based. Using qubits, certain tasks can be calculated faster, and information can be transmitted securely without the risk of interception.

Welte and his team want to build a quantum computer in the laboratory that can preserve and distribute the quantum-specific properties of the atomic qubits. In the future, such individual nodes could be used to build a complete network, a quantum network. “I want to build a small quantum computer with a network interface in Stuttgart that can be connected to other quantum computers to form a quantum internet,” explains Welte.

The new experiment is a customized setup for the planned quantum network applications. Two doctoral positions are planned. “We will also be offering interesting projects for Bachelor's and Master's theses,” says the physicist. His aim is to be able to position and manipulate all atoms individually in a very controlled manner in a space between two highly reflective mirrors. The mirrors are only half a millimeter apart. “It is possible to control the atoms with laser light, with so-called optical tweezers - in a vacuum, at extremely low temperatures,” explains the physicist.

Farinacci's early career research group investigates the magnetic properties of atoms - a topic she has been working on since her doctorate. “We capture images of an atom, for example on a surface,” explains Farinacci. “In order to understand the quantum nature of atoms, technology is now so advanced that it allows us to explore different ways to record atomic videos.” Fast, temporal changes in particular are extremely interesting for gaining a fundamentally better understanding of the dynamic magnetic behavior of materials on length scales of nanometers.

Such experiments are important because they can help, for example, to better understand qubits based on magnetic quantum effects in the future. This improved understanding could lead to better control of qubits compared to current capabilities, either by increasing the time during which these qubits keep their quantum properties or by controlling their quantum nature dynamically. This will pave the way for more powerful quantum computers.

Farinacci's CZS Junior Research Group is based with Prof. Sebastian Loth at the Institute for Functional Matter and Quantum Technologies (FMQ). “Our different fields of expertise complement each other perfectly,” says the physicist. There will be at least one doctoral position in the early career research group, and students can also write their Bachelor's or Master's theses at the institute.

Laëtitia Farinacci studied physics at the École Polytechnique near Paris and at the FU Berlin. She completed her doctorate at the FU Berlin in 2020. She then spent three years as a post-doctoral researcher at Delft University of Technology. This was followed by a year as a visiting researcher at the FU Berlin. Since February 2024, Farinacci has headed the CZS Junior Research Group for Quantum Photonics "Dynamic Control on the Atomic Scale" at the University of Stuttgart.

Stephan Welte studied physics in Freiburg and earned his doctorate from Munich in 2019, completing his doctoral thesis at the Max Planck Institute of Quantum Optics. He remained there as a postdoc until he moved to ETH Zurich in 2022. In August 2024, Welte became head of the new CZS Junior Research Group for Quantum Photonics "Quantum Network Nodes" at the University of Stuttgart.

About the CZS Center QPhoton
The CZS Center QPhoton, founded in 2022, is based at the universities of Stuttgart, Ulm and Jena. The center, which is funded by the Carl-Zeiss-Stiftung with 12 million euros, offers around 50 scientists a cross-disciplinary and cross-location platform for research and exchange in the innovative fields of quantum sensor technologies, quantum imaging processes and quantum information processing. Four CZS Junior Research Groups for Quantum Photonics will be established at the CZS Center QPhoton in the near future. Each project has a duration of five years and is funded with 700,000 euros. Two of the groups are based in Stuttgart.

About the Carl-Zeiss-Stiftung
The Carl-Zeiss-Stiftung’s mission is to create an open environment for scientific breakthroughs. As a partner of excellence in science, it supports basic research as well as applied sciences in the STEM subject areas (science, technology, engineering and mathematics). Founded in 1889 by the physicist and mathematician Ernst Abbe, the Carl-Zeiss-Stiftung is one of the oldest and biggest private science funding institutions in Germany. It is the sole owner of Carl Zeiss AG and SCHOTT AG. Its projects are financed from the dividend distributions of the two foundation companies.

The University of Stuttgart, with its strong research profile Quantum Technologies, spans a broad spectrum of fundamental research, all the way to the development of cutting-edge applications through generously funded, international, cooperation projects.

In 2014, the University of Stuttgart, the University of Ulm, and the Max Planck Institute for Solid State Research founded the Center for Integrated Quantum Science and Technology (IQST) as a hub for both basic and application-oriented research. This centre is being funded by the Carl-Zeiss-Stiftung with a further eight million euros.

IQST has been home to the office of the state initiative QuantumBW since 2023. This bundles research activities and initiatives in Baden Württemberg.

Researchers at the University of Stuttgart are also heavily involved in several projects at the Competence Center Quantum Computing Baden Württemberg. The center has set itself the goal of advancing the key technology of quantum in Baden-Württemberg and across Germany.

Quantum researchers at the University of Stuttgart have access to excellently equipped laboratories at the Center for Applied Quantum Technology (ZAQuant). Opened in 2021, the research building is considered one of the most modern of its kind. Researchers here are developing innovative nanophotonic quantum sensors.