Entanglement and Criticality in Quantum Impurity Systems
Abstract
We investigate the entanglement between a spin and its environment in impurity systems which exhibit a second-order quantum phase transition. As an application, we employ the spin-boson model, describing a two-level system (spin) coupled to a subohmic bosonic bath with power-law spectral density, J(ω) ωs and 0<s<1. Combining Wilson's Numerical Renormalization Group method and hyperscaling relations, we demonstrate that the entanglement between the spin and its environment is always enhanced at the quantum phase transition resulting in a visible cusp (maximum) in the entropy of entanglement. We formulate a correspondence between criticality and impurity entanglement entropy, and the relevance of these ideas to Nano-systems is outlined.
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