For most of a century, physicists have treated quantum entanglement as a fragile trait of the very small — a pair of photons, a handful of atoms, carefully shielded from the noise of the everyday world. A study published in Nature Physics now shows it surviving on a far grander stage: inside a centimetre-sized crystal you could comfortably hold in one hand.
The work was led by experimentalists at TU Wien, together with colleagues at the University of Würzburg, Rice University and the Institut Laue-Langevin (ILL) in Grenoble. Their sample was a "strange metal" made of cerium, palladium and silicon, Ce3Pd20Si6, a material long known for quantum behaviour that researchers still only partly understand.
Rather than trying to place the whole crystal into a Schrödinger's-cat-style superposition, the team asked a different question: are the crystal's countless constituents collectively locked into an entangled state? Prof. Silke Bühler-Paschen compares it to an anthill — disturb it and the colony responds as one, not as a single ant.
Nine partners, measured with neutrons
To read out that collective behaviour, the researchers borrowed a tool from quantum information theory called quantum Fisher information, which gauges how sharply a system reacts to a small perturbation. A collection of independent particles can only respond so much; an entangled system reacts more strongly than the sum of its parts. The theoretical groundwork was laid by Innsbruck physicist Peter Zoller and his colleagues.
At the ILL, PhD student Federico Mazza fired neutrons at the crystal using the cold-neutron spectrometer ThALES, cooling the sample to 60 millikelvin and tuning a magnetic field to 1.73 tesla — the precise point where the material sits at the edge of a transition tied to the breakdown of so-called Kondo screening. "In a normal material, one would expect a neutron to transfer its energy to an individual particle," Mazza said. Instead, the data pointed to groups of at least nine entangled entities acting together — what the authors describe as the largest entanglement depth reported so far in any quantum material.
The finding also offers a clue to a puzzle. In 2025, TU Wien and Rice reported that current flows through strange metals with unusually little electrical noise; coordinated, entangled particles may be the reason. "Strong entanglement appears to be directly linked to the unusual behaviour of strange metals," said lead theorist Fakher Assaad of the University of Würzburg.
The team now hopes the exchange can run both ways, exploring whether strange metals might one day serve quantum technologies such as ultra-sensitive metrology.