16. June 2026

Many quantum effects can only be observed when a small number of particles is studied — individual atoms, molecules or photons, for example, carefully shielded from the rest of the world. But what about macroscopic objects, consisting of an unimaginably large number of particles? Can they, too, display effects that provide a direct glimpse into the quantum world?

Experimentalists at TU Wien now showed that this is possible: a centimetre-sized crystal of a so-called strange metal was investigated, and a high degree of quantum entanglement was evidenced. This was made possible by a clearly defined method from quantum information theory: the quantum Fisher information.

It establishes a new bridge between solid-state physics and quantum physics: quantum entanglement can be directly quantified in a macroscopic strange-metal material.

Cats or ants?

The question of whether the strange statements of quantum theory can also be applied to large, macroscopic objects is almost as old as quantum theory itself. Erwin Schrödinger famously asked whether a cat could be both dead and alive at the same time. Since then, many experiments have attempted to generate quantum effects deliberately in ever larger systems.

“Our approach is different,” says Prof. Silke Bühler-Paschen from the Institute of Solid State Physics at TU Wien. “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 entanglement.” The experiment is therefore less reminiscent of Schrödinger’s cat than of an anthill:.when it is disturbed, it is not a single ant that reacts, but the entire colony as a collective.

Quantum Fisher information: entanglement enhances sensitivity

The theoretical basis for this approach was developed by the Innsbruck quantum physicist Peter Zoller and his team. They showed that the concept of quantum Fisher information can be used to detect quantum entanglement even 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 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 produced a crystal made of cerium, palladium and silicon — a strange metal already known to display highly intriguing quantum properties, many of which are still not fully understood. At the ILL in Grenoble, PhD student Federico Mazza bombarded the crystal with neutrons and measured how the material responded.

One neutron asks a question — at least nine particles answer

“In a normal material, one would expect a neutron to transfer its energy to an individual particle,” says Mazza. “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.” This provides direct evidence of high multipartite quantum entanglement in a solid — a macroscopic object large enough to be comfortably held in one’s hand.

The background: research on strange metals

The scientific motivation for the study was to better understand the strange-metal behaviour of the crystal — behaviour that is also observed in other classes of materials, such as high-temperature superconductors. In recent years, research on this topic has intensified, and more and more unusual properties have come to light. In a collaboration between TU Wien and Rice University in the United States, it was found in 2025 that electric current flows through such materials in an astonishingly “quiet”, low-noise manner. The discovery of entanglement now provides a new possible explanation for this phenomenon: the particles have not disappeared, but coordinate to suppress current 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 behaviour of strange metals.”

“The results are a great success for us,” says Silke 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 next goal is already set: “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.”

Original publication

F. Mazza et al., Quantum Fisher information in a strange metal, Nature Physics (2026). DOI: 10.1038/s41567-026-03298-0 https://www.nature.com/articles/s41567-026-03298-0