Quantum networks are considered a key technology for secure communication and digital sovereignty. In the EU-funded 'Superspin' project, researchers at the Karlsruhe Institute of Technology (KIT) are working with partners from Finland, the Czech Republic and the Netherlands to develop an interface between a superconducting quantum computer and a spin-based quantum memory.

"Many quantum systems are currently working independently of each other," explains Professor David Hunger from the KIT Institute of Physics. "In the Superspin project, we are developing a technology with which a quantum computer and a quantum memory can be reliably coupled. In this way, we are also creating the basis for linking quantum computers in the future, realizing distributed quantum computing and building a quantum internet."

Development of special quantum transducers

The technical challenge lies in combining two systems that are based on different physical principles. Superconducting qubits work in the microwave range, while diamond-based quantum memories store information in spin states and are addressed with visible light. In order to couple both components, the researchers are developing so-called quantum transducers. These convert quantum states into individual photons whose wavelength is adapted to the telecommunications band so that they can be transmitted via optical fibers.

A quantum memory made of special diamond defects that combine light and spin properties is being created at KIT for this purpose. The memory will be compatible with one of the two transducers so that the converted photons can be efficiently stored and retrieved when required. "Our project goal is to connect the physically completely different systems and create an entanglement between a superconducting qubit and a spin-based quantum memory," says Hunger. "This would not only be a technical breakthrough, but also an important step towards modular and scalable quantum technologies."

'Superspin' as part of the 'Pathfinder' program

The Superspin project is one of 44 projects that the European Innovation Council is funding with a total of over 140 million euros as part of the Pathfinder program. The partners involved are Aalto University (Finland), Palacký University in Olomouc (Czech Republic) and the Dutch start-up 'QphoX'.