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For more than 60 years, Bell's theorem has been the gold standard for demonstrating that quantum mechanics defies the rules of classical physics. Now, an international team of researchers, including Constructor University Professor Dr. Nicolas Gisin, has extended this principle to new limits, using an “elegant triangle” to reveal new forms of quantum nonlocality that specifically emerge in multi-node quantum networks. The study, published in leading physics journal Physical Review Letters, opens a new frontier in our understanding of how quantum correlations behave in realistic network settings, one that could help usher in the age of Quantum Internet.
"This is not simply a more elaborate version of Bell's theorem applied to networks, it's something genuinely new that only emerges when multiple independent quantum sources interact through entangled measurements," explained Dr. Gisin, who collaborated on the experiment with researchers from China, France and Austria.
Bell’s theorem, recognized with the 2022 Nobel Prize in Physics, demonstrated that a pair of entangled particles separated by a large distance and measured at random can somehow remain connected and exhibit correlations beyond what any classical physics theory can explain, a phenomenon known as quantum nonlocality. This counterintuitive behavior puzzled classical physicists like Albert Einstein, who rejected the idea that the particles’ physical properties only become determined upon measurement, famously quipping that “God does not play dice.” Yet decades of experiments have confirmed that nature does, in fact, appear to “play dice” when it comes to probabilistic quantum rules.
Whereas Bell tests typically feature a single source of entangled particles distributed to two observers who randomly choose which measurements to perform, the latest experiment from Dr. Gisin et. al. pushed the limits of nonlocality to new levels of complexity by using three observers arranged as the nodes of a triangle network. Each node received particles from two of the three independent sources and performed the same fixed measurement—eliminating the random measurement choice entirely.
These seemingly modest shifts introduce a profound new layer of complexity, like moving from a two to three-dimensional world. Rather than a single shared source, each observer measured particles from two independent sources, creating a more complex web of relationships. The results were striking: even in this distributed, multi-source configuration with no random measurements, correlations between all three sources were observed that defy all classical physics models. The findings demonstrate a distinct form of network nonlocality called “genuine quantum network nonlocality,” that emerges from the network structure itself and cannot be reduced to a standard two-particle Bell scenario.
To achieve this, the team generated what is known as the "elegant distribution," a specific pattern of correlations predicted to exhibit this network-dependent behavior. Using machine learning techniques and sophisticated mathematical analysis, the researchers showed that these correlations cannot be reproduced by any classical model, even one that allows complex patterns of hidden variables shared within the triangular network.
"The elegant distribution is genuine to the triangle network in a precise sense,” explained Dr. Gisin. “This cannot be reduced to standard Bell tests embedded within a more complex setup. It demonstrates quantum behavior that is uniquely a network phenomenon."
The findings suggest that quantum nonlocality is not limited to idealized lab settings, but extends to the kind of complex, realistic network structures that could underpin incoming quantum technologies. This is particularly relevant for the development of large-scale quantum networks aimed at connecting quantum devices across distances, often referred to as the “Quantum Internet.”
Demonstrating that nonlocal correlations can be created and verified in such networks using fixed measurements is an important step towards making these technologies viable, and advancing new forms of quantum security, verification and true randomness generation.
“The possibilities for downstream applications are quite exciting, as quantum networks evolve from laboratory demonstrations to real-world deployment,” said Dr. Gisin. “This includes advances in quantum security, such as device-independent cryptography, which could enable ultra-secure communication across future quantum networks.”
The experiment was conducted at the University of Science and Technology of China as part of an international collaboration involving institutions across China, Germany, Switzerland, Spain and France. Funding sources included the Innovation Program for Quantum Science and Technology, the National Natural Science Foundation of China, the European Research Council, and other agencies.
Looking ahead, Dr. Gisin said the work opens new avenues for both theory and experiment. “Just as Bell's theorem revealed that quantum particles are correlated in ways classical physics can’t explain, we now see quantum networks produce forms of correlation that go beyond even those scenarios,” he said. “It sets the stage for further experimentation and exploration into larger, more intricate quantum networks as we build towards scalable quantum internet.”
Dr. Nicolas Gisin, Professor of Physics, Constructor University
Nicolas.Gisin@unige.ch
https://doi.org/10.1103/5hhc-rw3t - "Experimental Genuine Quantum Nonlocality in the Triangle Network," Physical Review Letters, May 2026
Constructor University Physics Professor and Member of the Constructor Group Strategic Advisory Boar ...
Source: Constructor University
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