Quantum Magnetic Impurities in Magnetically Ordered Systems

TL;DR

This paper investigates a quantum impurity in a magnetically ordered system, revealing quantum frustration effects that influence decoherence and susceptibility, with implications for quantum computing and experimental measurements.

Contribution

It introduces a generalized dissipative two-level system model with two heat baths and demonstrates quantum frustration effects using RG and NRG methods.

Findings

Quantum frustration suppresses decoherence in the strong coupling regime.

Impurity magnetic susceptibility exhibits quasi-scaling behavior.

Predictions made for NMR experimental observations.

Abstract

We discuss the problem of a spin 1/2 impurity immersed in a spin S magnetically ordered background. We show that the problem maps onto a generalization of the dissipative two level system (DTLS) with two independent heat baths, associated with the Goldstone modes of the magnet, that couple to different components of the impurity spin operator. Using analytical perturbative renormalization group (RG) methods and accurate numerical renormalization group (NRG) we show that contrary to other dissipative models there is quantum frustration of decoherence and quasi-scaling even in the strong coupling regime. We make predictions for the behavior of the impurity magnetic susceptibility that can be measured in nuclear magnetic resonance (NMR) experiments. Our results may also have relevance to quantum computation.