A team at ETH Zurich in Switzerland has constructed a 30-metre cryogenic quantum communication link connecting two separate quantum computers, each housed inside its own specialised refrigeration unit.
Two new papers posted to the arXiv research server this week describe how the link functions and what it can already do. Neither has yet been peer-reviewed, but the hardware results are experimentally verified.
The challenge these researchers are solving is fundamental. Quantum computers of the type most likely to outperform conventional machines are built from superconducting circuits — components that only work at temperatures close to absolute zero, the coldest temperature anything can physically reach.
Absolute zero is minus 273 degrees Celsius. The ETH Zurich system operates at 50 millikelvin, which is 50 thousandths of a degree above absolute zero. That is roughly 50 times colder than the average temperature of deep space.
Getting a signal from one of these machines to another is not simply a matter of running a wire between them. Any connection has to maintain that extreme cold along its entire length, otherwise the quantum information it carries is destroyed by thermal noise before it arrives. Building a link that stays cold enough across 30 metres, while remaining modular enough to extend further, is precisely what the ETH Zurich team has achieved.
The link is constructed in segments of 5, 10, and 30 metres. The full 30-metre system takes about six and a half days to cool down to its operating temperature after assembly. Once cold, it connects two dilution refrigerators through a quantum communication channel that preserves the fragile quantum states being transmitted.
To confirm the link is doing genuine quantum communication and not just copying classical signals, the researchers performed a loophole-free Bell test. This is a rigorous physics experiment that can only give a positive result if the two ends of the system are truly sharing quantum non-locality, a property that has no equivalent in ordinary physics and that forms the foundation of quantum communication security. The test passed.
A second paper from the same group demonstrates an additional capability built on the same platform. When you send signals down a communication channel, being able to carry multiple independent messages at the same time is essential for any practical network.
The ETH Zurich team showed that individual microwave photons, the particles that carry quantum information at these frequencies, can be shaped into three distinct pulse patterns that do not interfere with each other. A receiver can selectively absorb one pattern and reflect the other two with a selectivity ratio of 40, meaning the channels stay almost entirely separate. This is the quantum equivalent of tuning to one radio station while ignoring two others playing on the same wire simultaneously.
The significance of these results is not that quantum computers will suddenly be networked together next year. The systems involved are still research instruments, and scaling cryogenic links from 30 metres to the distances needed for practical quantum data centres remains a considerable engineering challenge. What these papers establish is that the physics works at real distances, that the hardware can be built in modular form, and that multiplexing is achievable within the same platform.
Quantum computers connected through verified quantum links would offer capabilities that no ordinary network can match. Quantum communication channels are physically impossible to eavesdrop on without detection, because any measurement of a quantum state disturbs it in a way that reveals the intrusion. Distributed quantum computing, where multiple processors work together on problems too large for any single machine, also becomes possible once processors can reliably exchange quantum information.
Sources
The infrastructure paper is arXiv:2604.15971, submitted 17 April 2026. The multiplexing paper is arXiv:2604.12947. Both are from the research group of Andreas Wallraff at ETH Zurich.
Primary sources
Schär, J.D., Storz, S., Magnard, P., Kurpiers, P., Lütolf, J., Gehrig, M., Besse, J.-C., Kulikov, A., Wallraff, A. “A Modular Cryogenic Link for Microwave Quantum Communication Over Distances of Tens of Meters.” arXiv:2604.15971 [quant-ph]. Submitted 17 April 2026. https://arxiv.org/abs/2604.15971
“Emission and Absorption of Microwave Photons in Orthogonal Temporal Modes across a 30-Meter Two-Node Network.” arXiv:2604.12947. Submitted ~14 April 2026. https://arxiv.org/abs/2604.12947
Background and context sources consulted during research
ETH Zurich Wallraff Group — prior cryogenic quantum link work referenced in both papers: Magnard et al. (2020), “Microwave quantum link between superconducting circuits housed in spatially separated cryogenic systems.” Physical Review Letters 125, 260502. https://arxiv.org/abs/2007.01859
Storz et al. (2023), “Loophole-free Bell inequality violation with superconducting circuits.” Nature 617, 265–270. https://www.nature.com/articles/s41586-023-05885-0
Storz et al. (2025), “Cryogenic microwave link for quantum local area networks.” npj Quantum Information. https://www.nature.com/articles/s41534-025-01046-5
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Ray Jackson holds a BSc in Electrical Engineering from the University of Manitoba and a PhD in Physics from Carleton University. His reporting interests include Current and Future Technologies, Engineering and Artificial Intelligence.