For most of us, quantum physics feels like something that belongs in the invisible world of atoms and photons.
Focusing on a crystal as small as a centimeter of a strange metal, they saw clear signs of quantum entanglement across not just single atoms but entire scales that an amorphous solid could describe.
To achieve this, quantum Fisher information (QFI), a concept in quantum information theory, was used.
A collaboration between TU Wien and Rice University showed in 2025 that electrical charge flowing through these materials can unexpectedly “quiet” low-noise.
This shows that quantum entanglement is not merely confined to the microscopic regime but can be quantified in a macroscopic sample you can grip.
For most of us, quantum physics feels like something that belongs in the invisible world of atoms and photons. It’s the science of the very small, where particles can be in two places at once, or mysteriously linked across space. But scaling these phenomena up raises a pragmatic question: could they become too large (more or less) to hold in your hand and still exhibit a measurable quantum effect?
At TU Wien, researchers have shown that the answer is yes. Focusing on a crystal as small as a centimeter of a strange metal, they saw clear signs of quantum entanglement across not just single atoms but entire scales that an amorphous solid could describe.
In a paper published in Nature Physics, the authors present a tangible connection between commonly observed properties of materials and the fundamental quantum mechanics that underpin them.
Since the very beginning of quantum theory, there has been controversy over whether or not quantum effects occur in large objects. The original Schrödinger’s cat thought experiment was formulated to highlight the apparent absurdity of applying quantum rules to macro-sized objects.
But the TU Wien team took a different approach. “We do not try to bring the crystal as a whole into a superposition of two states,” says Prof. Silke Bühler‑Paschen from the Institute of Solid State Physics at TU Wien.
“Instead, we ask whether its constituents are, collectively, in such a state of entanglement.”
Instead of Schrödinger’s cat, she compares the phenomenon to an anthill: disturb one ant and its colony reacts as a unit. Analogously, particles entangled in the crystal do not just scatter as isolated entities; their response is organized by their quantum-interconnected states, a phenomenon that cannot be explained by classical physics.
To achieve this, quantum Fisher information (QFI), a concept in quantum information theory, was used. Physicist Peter Zoller and his group in Innsbruck originally introduced QFIs. They now offer a mathematical way to detect entanglement in large many-body systems.
“The quantum Fisher information quantifies how sensitively a quantum system responds to a change,” explains Bühler‑Paschen. “For a collection of independent particles, the response is limited because each particle contributes on its own. However, if the particles are entangled, the entire system can respond more strongly than the sum of its individual parts.”
“This enhanced sensitivity is precisely what makes entanglement such a valuable resource for quantum metrology, where one aims to detect extremely small signals with the highest possible precision. By measuring how strongly a system responds to a perturbation, one can therefore infer the degree of entanglement present in the material.”
The TU Wien team then synthesized a cerium-palladium-silicon crystal, a well-studied strange metal known to exhibit unusual quantum properties. Ph. at the Institut Laue-Langevin (ILL) in Grenoble, in the setup of their experiment, D. student Federico Mazza bombarded the crystal with neutrons to analyze how they scatter.
“In a normal material, one would expect a neutron to transfer its energy to an individual particle,” Mazza explains. “But by analyzing the data using the quantum Fisher information, we found a response that cannot be explained in terms of independent particles. Instead, it indicates that groups of at least nine quantum‑entangled entities act collectively.”
In this regard, it provides direct evidence of multipartite entanglement in a macroscopic solid (a readily visible crystal).
The motivation behind the study was to understand better the peculiar behavior of strange metals, a class of materials that also includes high‑temperature superconductors. A collaboration between TU Wien and Rice University showed in 2025 that electrical charge flowing through these materials can unexpectedly “quiet” low-noise.
A potential explanation is that it was a consequence of their charge carriers not going missing but reacting (or, more to the point, coordinating) as a thermal reducer in response to temperature fluctuations.
“What we see here is not a detail of one particular material, but a general physical principle,” says Fakher Assaad from the University of Würzburg, lead theorist of the work. “Strong entanglement appears to be directly linked to the unusual behavior of strange metals.”
“The results are a great success for us,” says Bühler‑Paschen. “They confirm that our unusual approach of using methods from quantum information science for solid‑state physics studies of novel materials can reveal fundamentally new insight.”
The team’s next goal is to see whether strange metals might one day find applications in quantum technologies. “We want the transfer of knowledge between the two fields to also work in the other direction. Our aim is to explore whether strange metals may one day find applications in quantum technologies, for example, in high‑precision measurements for quantum metrology.”
But far from a laboratory curiosity. This shows that quantum entanglement is not merely confined to the microscopic regime but can be quantified in a macroscopic sample you can grip. The odd metal seems to function in a way analogous to the one that allows billions of ants living together within the same anthill to act collectively, with trillions of particles synchronizing their actions.
The discovery shows that we can observe quantum mechanics not only in tiny particles but also in larger objects. It suggests that the boundary between the quantum world and our everyday world is thinner than we believed. For everyone else, it’s a reminder that even an ordinary-looking crystal can hide incredible secrets inside, like quiet quantum whispers resonating through the universe.
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