Quantum Fisher information in a strange metal

A strange metal is an exotic state of correlated quantum matter, and intensive efforts are ongoing to understand its nature. Here we show that the quantum Fisher information-a concept from quantum metrology-may provide helpful insights. We use inelastic neutron scattering and quantum Monte Carlo simulations to study quantum critical fluctuations of the Kondo destruction type, which are considered to underlie strange metal behaviour in heavy-fermion compounds. We find that the associated quantum Fisher information increases strongly and without a characteristic scale as the strange metal forms with decreasing temperature. This provides evidence for a quantum state with high multipartite entanglement and offers a positive descriptor of strange metallicity that points towards its microscopic basis. Our work opens a direction for future studies across a range of strange metal platforms.