Long-Range Entanglement near a Kondo-Destruction Quantum Critical Point

The numerical renormalization group is used to study quantum entanglement in the Kondo impurity model with a density of states rho(epsilon) proportional to vertical bar epsilon vertical bar(r) (0 < r < 1/2) that vanishes at the Fermi energy epsilon = 0. This nonintegrable model features a Kondo-destruction quantum critical point (QCP) separating a partially screened phase from a local-moment phase. The impurity contribution S-e(imp) to the entanglement entropy between a region of radius R around the magnetic impurity and the rest of the system reveals a length scale R* that distinguishes a region R << R* of strong critical entanglement from one R>> R* of weak entanglement. Within each phase, S-e(imp) is a universal function of R/R* with a power-law decay for R/R* >> 1. The entanglement length R* diverges on approach to the interacting QCP, showing that the critical Kondo screening cloud subsumes the entire system as the impurity becomes maximally entangled with the conduction band. This work has implications for entanglement calculations in other models and for the nature of heavy-fermion quantum criticality.