Neutral atoms, lattices of laser light, entanglements – the processing and memory components of quantum computers can be made from these. The more of these qubits that work without errors, the more powerful a quantum computer can be. Qubits made of neutral atoms are considered promising in this context. In order to advance the development of this technology, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) has awarded a contract. The start-up Planqc, based in Garching, near Munich, will develop a quantum computer based on neutral atoms within three and a half years. The contract has a value of 29 million euros.
Atoms – in contrast to charged ions – are electrically neutral. All atoms of the same isotope of an element have the same properties. Planqc therefore uses them in their ‘ground state’ for quantum computing: “In order for the neutral atoms to become qubits, they must first be trapped and confined in a vacuum by laser beams,” says Robert Axmann, Head of the DLR Quantum Computing Initiative (QCI). The atoms are then arranged regularly, similar to eggs in a carton, and can be manipulated with lasers. This is how individual qubits are created. “To have two qubits interact with each other, the atoms are excited into so-called Rydberg states. Without an interaction and entanglement between qubits, quantum computers do not work,” Axmann explains.
In atoms in the Rydberg state, the outermost electron in the atomic shell is much further away from the atomic nucleus than normal. This makes the atoms a thousand times larger. In very simplified terms, this leads to a Rydberg atom ignoring neighbouring atoms and interacting with a more distant Rydberg atom beyond them. This is how atomic shells become the computational building blocks of quantum computers.
Development work in close proximity to DLR institutes and other start-ups
Planqc is now creating a prototype quantum processor using this technology. It is to grow to a system with more than 100 qubits. The quantum computer is also to be scalable and, in the future, error correctable. This means that the number of qubits can be increased, and the system will work error-free. Error-proneness is considered one of the biggest obstacles in quantum computing.
Planqc uses offices and laboratories at the DLR Innovation Center in Ulm for its development work. In the immediate vicinity of the DLR institutes, start-ups and companies here are already producing quantum computers based on nitrogen vacancies in diamond, photonic quantum computers, hybrid systems with analogue computers and spin-enabling technologies on behalf of the QCI. At the second DLR Innovation Center in Hamburg, research is being conducted on quantum computers based on ion traps. The application process for solid-state quantum computers ended recently.
“Diversity is an important feature of the DLR Quantum Computing Initiative. The QCI pursues different technological approaches to investigate their respective advantages and disadvantages. With this project, we are adding another promising technology to our quantum computing portfolio at the Ulm site,” says Karla Loida, Hardware Lead for the QCI. It is not yet clear which architectures for quantum computers will prevail. Some are already relatively advanced, such as superconducting systems, but these need extremely low temperatures. There are other systems that could be considered for quantum computers, but which have not yet been explored in depth.