A quantum computer based on individual Rydberg atoms is being developed at the 5th Physics Institute of the University of Stuttgart. A significant milestone has now been reached with the commissioning of a highly sophisticated laser-optical system, which was developed in close collaboration with the Fraunhofer Institute for Laser Technology ILT in Aachen. The system can precisely control up to 2,000 atoms, which is a key prerequisite for scaling the quantum computing platform being developed at the institute.
Patents lay the foundation for technology transfer
Since 2021, the research team at the 5th Physics Institute has been developing a novel quantum computer architecture based on individual Rydberg atoms arranged in freely configurable atom arrays using optical tweezers. Group leader Florian Meinert and his team have filed patent applications for a comprehensive set of key technologies for this platform, including a novel fast fine-structure qubit, an electric field control system compatible with a vacuum for sensitive Rydberg states, and a new method for creating dynamic qubit arrays. Together, these innovations form the technological basis for further development of the platform and its future technology transfer.
Precise control for scalable quantum computing
Neutral-atom quantum computers are widely regarded as one of the world's most promising approaches to powerful, scalable quantum computing (see the EuRyQa consortium white paper for more information). Following the successful experimental realization of the fine-structure qubit in 2024, the Stuttgart team is now focusing on system scalability. The long-term goal is to execute quantum algorithms involving hundreds of qubits.
To accomplish this, the researchers developed a laser-optical system that can generate up to 2,000 individually addressable laser beams. These beams form optical tweezers that trap and position Rydberg atoms inside an ultra-high-vacuum chamber. Twenty acousto-optic modulators control the beam positions, allowing the atom positions to be dynamically rearranged in just a few microseconds while a quantum algorithm is running. This dynamic qubit connectivity is a distinctive feature of neutral-atom quantum computing platforms, enabling entirely new classes of quantum circuits.
Joint development with Fraunhofer ILT
The Fraunhofer Institute for Laser Technology ILT in Aachen specifically designed and built the laser-optical system to meet the requirements of the Stuttgart quantum computer project. The ILT developed its specifications in close collaboration with researchers at the 5th Institute of Physics, who defined the physical requirements of the quantum processor architecture.
Despite its high level of integration, the resulting optical system comprises more than 150 individual components and occupies only about one square meter.
"We have now integrated the nearly 300-kilogram system into our experiment and carried out the first tests to determine whether we can control the atoms with the required precision. Controlling the optics is also challenging because more than a thousand radio-frequency tones must be synchronized with high temporal precision. The dynamic qubit shuttling operations in our system resemble those of an abacus," explains Florian Meinert.
Another step toward a quantum computer
The successful integration of the laser-optical system brings the realization of a scalable quantum computer based on Rydberg atoms at the 5th Institute of Physics significantly closer. The team plans to use its ‘quantum abacus’ to investigate fault-tolerant quantum computing architectures with several hundred to as many as one thousand qubits.
Neutral atoms as the basis for future quantum computers
Neutral atoms—in our case, strontium atoms—are trapped, held, and manipulated using laser beams before being excited into highly excited Rydberg states. In these states, the electron orbit expands dramatically. Quantum information (0, 1, or a superposition of both) is encoded in the energy levels of the neutral atoms, which serve as qubits.
A quantum logic gate is formed when two atoms are excited simultaneously to Rydberg states and interact with one another. The interaction is so strong that neighboring atoms cannot be excited at the same time, a phenomenon known as the Rydberg blockade. The coupled Rydberg atoms thus form a quantum gate that can perform computational operations. The resulting quantum states are highly stable because the atoms are effectively isolated from their environment inside an ultra-high-vacuum chamber.
Part of Germany's and Baden-Württemberg's quantum initiative
The Rydberg quantum computer project (QRydDemo) is funded by the German Federal Ministry of Research, Technology and Space (BMFTR) as part of its Quantum Systems research program. The project is also part of the QuantumBW initiative in Baden-Württemberg and is integrated into the Carl Zeiss Foundation Center for Quantum Photonics (CZS Center QPhoton).
The 5th Institute of Physics is working with numerous partners from academia and industry to translate fundamental research into market-ready quantum technologies and strengthen a competitive quantum ecosystem in Baden-Württemberg.