New building block for the quantum internet

The development of quantum technologies is progressing, with quantum computers in particular promising breakthroughs in medicine, materials science and cryptography. However, they only develop their full potential when they are networked. "At the moment, many quantum systems work 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."

To connect the systems, qubits are converted into photons, known as "flying qubits", which travel almost loss-free over fiber optic cables. With the help of quantum entanglement, quantum states can be reliably transferred from one system to another.

The coupling of different systems is particularly technically challenging: superconducting qubits work in the microwave range, while diamond-based quantum memories use light in the visible wavelength range. Special quantum transducers convert the states and adapt the photons for transport via fiber optic cables. At KIT, a quantum memory made of diamond defects is being developed that combines light and spin properties and can store the photons. "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.

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