Researchers at TU Wien have detected high-degree quantum entanglement within a centimeter-sized crystal of a “strange metal,” proving that macroscopic objects can exhibit collective quantum behavior. Using the quantum Fisher information technique, the team observed how particles within the cerium, palladium, and silicon material act in coordinated groups rather than as independent entities.
Strange metals deviate from conventional materials, often exhibiting unusual quantum properties that remain only partly understood. This phenomenon suggests a state of matter where particles are so strongly correlated that they no longer behave as individual units, but as a highly integrated system.
Moving from Schrödinger’s cat to an anthill model
For decades, the physics community has debated whether the strange, non-intuitive rules of quantum mechanics apply only to microscopic particles or if they can manifest in larger, visible objects. While Erwin Schrödinger’s famous thought experiment involving a cat in a state of superposition remains the standard metaphor for quantum uncertainty, TU Wien has detected strong quantum entanglement using a different conceptual framework.
Instead of attempting to force a large object into a single state of superposition, the researchers focused on the collective coordination of the particles within the material.
“Our approach is different. 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.” Prof.
Bühler-Paschen compares this collective behavior to an anthill. In such a system, a disturbance does not trigger a reaction from a single ant, but rather from the entire colony acting as one coordinated unit.
Quantifying entanglement through quantum Fisher information
The ability to measure this coordination in a large-scale material relies on a theoretical framework developed by Innsbruck quantum physicist Peter Zoller. The team utilized quantum Fisher information, a tool from quantum information science that quantifies how sensitively a quantum system responds to external changes.
In a standard material, a system’s response to a perturbation is limited because each particle contributes to the reaction independently. However, an entangled system can respond more strongly than the sum of its individual parts. This enhanced sensitivity allows researchers to infer the degree of entanglement present by measuring the strength of the material’s reaction to a disturbance.
This measurement technique is central to the field of quantum metrology, where one aims to detect extremely small signals with the highest possible precision.
Collective responses in cerium, palladium, and silicon crystals
To test this, the researchers produced a crystal composed of cerium, palladium, and silicon. This specific material is classified as a “strange metal,” a category of matter known for unusual properties that continue to challenge current physical models.
The experimental phase took place at the ILL in Grenoble, France, where the team subjected the crystal to neutron bombardment.
By analyzing how the crystal reacted to these neutrons, the researchers were able to observe the internal particle dynamics.
"In a normal material, one would expect a neutron to transfer its energy to an individual particle. But by analyzing the data using the quantum Fisher information, we found a response that cannot be explained in terms of independent particles.
Bridging solid-state physics and quantum information
The findings, which were published in Nature Physics, establish a direct link between the fields of solid-state physics and quantum information theory. By demonstrating that entanglement can be measured directly in a macroscopic strange metal, the research provides a new way to study materials that have long been poorly understood.
This discovery has significant implications for the future of quantum metrology.
Furthermore, understanding the collective behavior of these particles may offer insights into the mechanics of high-temperature superconductors, as similar behavior appears in those materials. In 2025, researchers from TU Wien and Rice University reported that electrical current moves through strange metals with unusually low electrical noise; the discovery of entanglement may help explain why particles coordinate their behavior to suppress current fluctuations.
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