Scientists at TU Wien have detected strong quantum entanglement inside a crystal large enough to hold in one hand, offering new evidence that quantum effects usually associated with single atoms or photons can also appear in macroscopic materials.
Quantum phenomena are typically studied in tiny, carefully isolated systems. Whether the same effects can occur in larger objects has been debated since the early days of quantum physics, famously illustrated by Erwin Schrödinger's thought experiment about a cat that is simultaneously alive and dead until observed.
The TU Wien team took a different approach. Rather than trying to place an entire crystal into a superposition of two states, they asked whether the particles inside it were collectively entangled. Prof. Silke Bühler-Paschen, from the university's Institute of Solid State Physics, compares the idea to an anthill: when disturbed, the colony as a whole responds, not any single ant acting alone.
Measuring entanglement through sensitivity
The experiment relied on a concept called quantum Fisher information, a framework developed by Innsbruck physicist Peter Zoller and colleagues, which shows that entanglement can be identified even in systems containing enormous numbers of interacting particles.
According to Bühler-Paschen, quantum Fisher information measures how sensitively a system responds to a disturbance. Independent particles produce only a limited response, but entangled particles can make the whole system react far more strongly than the sum of its parts. By measuring the strength of that response, researchers can estimate how much entanglement is present, a principle also relevant to quantum metrology, where extremely small signals must be detected with high precision.
To test this, the team examined a crystal made of cerium, palladium and silicon, a member of a class of materials known as strange metals that display unusual and only partly understood quantum properties.
At the Institut Laue-Langevin in Grenoble, PhD student Federico Mazza fired neutrons at the crystal and analyzed how it responded. "In a normal material, one would expect a neutron to transfer its energy to an individual particle," Mazza said. Instead, the data pointed to a collective response that could not be explained by independent particles, indicating groups of at least nine quantum-entangled entities acting together.
The findings provide direct evidence of strong, multipartite quantum entanglement inside a solid crystal large enough to fit in the palm of a hand.
Why it matters for strange metals
The researchers originally aimed to understand why strange metals behave so differently from conventional materials, a puzzle also relevant to high-temperature superconductors. In 2025, teams from TU Wien and Rice University had reported that electrical current moves through these materials with unusually low electrical noise. The newly observed entanglement may help explain that behavior, suggesting particles coordinate in ways that suppress current fluctuations.
"What we see here is not a detail of one particular material, but a general physical principle," said Fakher Assaad of the University of Würzburg, lead theorist on the project. "Strong entanglement appears to be directly linked to the unusual behavior of strange metals."
Bühler-Paschen called the results "a great success," confirming that combining quantum information methods with solid-state physics can reveal fundamentally new insight. The team now hopes to explore whether strange metals could eventually be useful for quantum technologies, including highly sensitive quantum metrology systems.
The study was published in Nature Physics.