Superconducting circuits are a strong contender for realizing quantum computing systems. Constructing such systems with many thousands, possibly millions of superconducting qubits will require linking several computing nodes housed in their dedicated cryogenic systems into a larger networked cluster. Such networks could operate at optical frequencies using fiber links but would require large bandwidth and high-fidelity microwave-to-optical conversion, which is currently unavailable. At ETH Zurich, in a radically different approach, we have designed, realized, and tested a quantum microwave link which allows superconducting-circuit-based quantum processors located in different cryogenic systems to directly exchange quantum information and generate entanglement [1] over meter-scale distances [2]. Quantum links, for a quantum computer, take the role of a network transferring data between computing nodes located in a high-performance computing data center. However, unlike its conventional counterparts, our data link is operated at ultra-low temperatures, close to absolute zero. This allows our quantum data link to directly connect to quantum processors operating at the same temperature. Realizing a quantum link across 30 meters we have demonstrated non-locality as a new resource accessible with superconducting circuits by performing the first loophole-free Bell test with superconducting qubits [3]. We have exploited this resource to create perfect randomness certified by quantum physics for the first time [4]. The system we have constructed is the only one of its kind in the world and could play an important role in both growing the power of quantum computers in the future and allowing for fundamental quantum science experiments.

[1] P. Kurpiers et al., Nature 558, 264-267 (2018)

[2] P. Magnard et al., Phys. Rev. Lett. 125, 260502 (2020)

[3] S. Storz et al., Nature 617, 265-270 (2023)

[5] A. Kulikov et al., Nature 653, 1033 (2026)