Quantum entanglement has long been observed in tiny, carefully isolated groups of particles. Scaling that effect up to objects visible to the naked eye has been a much harder problem. Now researchers at the Vienna University of Technology have reported detecting a high degree of quantum entanglement inside a centimeter-sized cube of material, a result that pushes the boundaries of what physicists thought was observable at that scale.
The material they used belongs to a class known as strange metals. These substances behave in unusual ways. Their electrical resistance increases sharply when warmed, and at lower temperatures they become superconductive, though at higher temperatures than standard superconductive materials. In a strange metal, electrons appear to lose their individual identity and move through the material as a kind of diffuse collective, rather than as separate particles. That behavior has long challenged the standard model of condensed matter physics.
The crystal tested by the TU Wien team was made of cerium, palladium, and silicon. To probe whether it contained quantum entanglement, the researchers bombarded it with neutrons and measured how it responded. The material did not behave like normal matter. Its responses could not be explained by treating its particles as independent. Instead, at least nine quantum-entangled entities were found to be acting together, demonstrating what researchers describe as high multipartite quantum entanglement in a solid object.
Professor Silke Bühler-Paschen from TU Wien described the approach. "We do not try to bring the crystal as a whole into a superposition of two states. Instead, we ask whether its constituents are — collectively — in such a state of entanglement," she said.
The finding, reported this week by Phys.org, does not mean that everyday objects like coffee mugs are quantum entangled. Strange metals are a specific and unusual class of material, and the conditions required to observe entanglement in them are tightly controlled. But the result does show that quantum entanglement is not strictly limited to the microscopic world, and that it can survive and be detected in matter at a scale far larger than previously demonstrated.
The research adds to a growing body of work pushing at the edges of what quantum mechanics can describe, and raises deeper questions about the nature of electrons and collective behavior in condensed matter systems.
