QCNEWS
A Fraunhofer ISI and Saarland University roadmap finds no dominant platform has emerged for quantum repeaters — the relay devices a future quantum internet needs to carry quantum signals over long fiber links — and sets a before 2035 benchmark for
Europe's plan for a long-distance quantum network does not run through a single winning chip. A new roadmap from Fraunhofer ISI, a German applied-research institute, and Saarland University, released under Germany's SQuaD consortium for Quantum Communication Germany, finds that six competing hardware platforms for quantum repeaters remain roughly even, and that the field's own clock for the first long-distance demonstration runs out before 2035.
Quantum repeaters are the missing relay in a future quantum internet. Classical internet signals can be copied and amplified at will; quantum information cannot. That hard rule of physics, the no-cloning theorem, means a long fiber-optic link that carries quantum bits loses signal to noise faster than engineers can clean it up. A repeater for quantum signals has to do something classical repeaters do not: store an entangled quantum state, swap entanglement with the next node, and forward it down the line without ever measuring or copying the data it is carrying. The Fraunhofer ISI / Saarland roadmap treats getting that right as the central hardware problem of the field.
The team, led by Dr. Lukas Weymann of Fraunhofer ISI, ran a literature review, individual expert interviews, and a roadmapping workshop with 22 participants from academia and industry. Their conclusion, published as "Quantum Repeaters – A Technology Roadmap" and hosted as a PDF on the SQuaD site: no single hardware platform has pulled ahead.
The six platforms the roadmap evaluates all encode and store quantum states in different physical substrates. Color centers in diamond are atom-sized defects in a diamond lattice that hold a quantum state inside the crystal. Trapped atoms and ions are individual atoms held in place by electromagnetic fields, and are the most precise quantum memories in the lab. Warm and cold atomic ensembles store quantum states in large clouds of atoms, with cold clouds offering longer coherence. Rare-earth-ion-doped crystals embed rare-earth ions in a solid host for longer-lived quantum memory. Semiconductor quantum dots are nanoscale islands of semiconductor that emit single photons on demand. Each makes different trade-offs in storage time, efficiency, scalability, and compatibility with existing telecom fiber.
The roadmap does not pick a winner. Instead, it flags hybrid systems, or repeaters that use, say, a quantum-dot photon source feeding into a rare-earth memory, as a potentially important direction. That is a quieter finding than a winner-emerging headline, and it is the one the consortium chose to publish.
The applications column is clearer than the hardware column. Quantum repeaters, once they work at scale, unlock quantum key distribution (QKD), or communications whose security rests on physics rather than on the difficulty of factoring large numbers, over distances where direct links now lose too much signal. The same network fabric would let quantum computers pool processing power across sites and tie quantum sensor arrays into continent-scale instruments.
The roadmap's clearest deliverable is a deadline. The authors expect the first demonstrations of quantum repeaters transmitting entanglement or quantum information over long distances with lower losses than direct fiber connections to land before 2035. That is the field's own benchmark, written into a public document by the German consortium, and it is the line European funding agencies, hardware startups, and competing national programs will be measured against.
Open problems the roadmap names, including efficiency, storage times, transmission rates, telecom-infrastructure integration, standardization, and industrial scaling, are not new to anyone in the field. Putting them in a single document, with a clock attached, is.
The next checkpoint is not a product launch. It is whether the next round of European and partner-country experimental work, funded under SQuaD and adjacent programs, can post a long-distance repeater result that beats a direct fiber link before that 2035 line is reached.