Entanglement Peaks at the Quantum Critical Point of a Strange Metal

Rice University and TU Wien used inelastic neutron scattering at the Institut Laue-Langevin to probe a centimeter-sized Ce3Pd20Si6 crystal at 60 mK under 1.73 T, extracting quantum Fisher information as a bulk entanglement metric.

Schrödinger’s anthill: Quantum entanglement detected inside a centimeter-sized strange metal

Strange metals show linear-in-temperature resistivity and, in Ce3Pd20Si6, the quantum critical point marks Kondo screening collapse, driving the system into a non-Fermi-liquid regime with anomalous transport.

Schrödinger’s anthill: Quantum entanglement detected inside a centimeter-sized strange metal

The study was led by Qimiao Si (Rice) and Prof. Silke Bühler-Paschen (TU Wien), with PhD student Federico Mazza performing the neutron work and theorist Fakher Assaad (Würzburg). Funding came from the U.S. DOE, Air Force Office of Scientific Research, Robert A. Welch Foundation, and Vannevar Bush Faculty Fellowship.

Rice Physicists Measure Entanglement in Quantum Critical Metal

QFI density increased ~40-fold from 10 K to 60 mK, reaching 8.2 ± 0.9, which sets a lower bound of nine-partite entanglement. The spin quantum Fisher information peaked at the quantum critical point, confirming maximal entanglement at the phase transition.

Rice Physicists Measure Entanglement in Quantum Critical Metal

The result provides a bulk metric for multipartite entanglement, directly linking quantum correlations to the anomalous transport of strange metals. It also demonstrates that entangled electrons amplify collective response, suggesting applications in high-precision quantum sensing.

Rice Physicists Measure Entanglement in Quantum Critical Metal

Qimiao Si described the experimental determination as “really gratifying,” noting its validation of theory. Silke Bühler-Paschen emphasized the deliberate focus on collective entanglement rather than macroscopic superposition. Fakher Assaad said strong entanglement appears directly linked to strange-metal behavior.

Schrödinger’s anthill: Quantum entanglement detected inside a centimeter-sized strange metal

The authors note that competing theories of strange-metal physics remain unresolved and that a unified description of entanglement-driven criticality is still lacking, calling for additional experimental and theoretical investigations.

Schrödinger’s anthill: Quantum entanglement detected inside a centimeter-sized strange metal

• “In quantum critical metals, electrons act so collectively that they lose their individual identity,” — Qimiao Si, Rice University

Rice Physicists Measure Entanglement in Quantum Critical Metal

• “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.” — Prof. Silke Bühler-Paschen, TU Wien

Schrödinger’s anthill: Quantum entanglement detected inside a centimeter-sized strange metal

• “In a normal material, one would expect a neutron to transfer its energy to an individual particle,” — Federico Mazza, PhD student, ILL

Schrödinger’s anthill: Quantum entanglement detected inside a centimeter-sized strange metal

• “But by analyzing the data using the quantum Fisher information, we found a response that cannot be explained in terms of independent particles.” — Federico Mazza, PhD student, ILL

Schrödinger’s anthill: Quantum entanglement detected inside a centimeter-sized strange metal

• “What we see here is not a detail of one particular material, but a general physical principle,” — Fakher Assaad, University of Würzburg

Schrödinger’s anthill: Quantum entanglement detected inside a centimeter-sized strange metal

Future work will apply QFI-based entanglement diagnostics to other quantum-critical systems and explore strange metals as platforms for high-precision sensing. The full study appears in *Nature Physics*.

Schrödinger’s anthill: Quantum entanglement detected inside a centimeter-sized strange metal