Hidden Caldeira-Leggett dissipation in a Bose-Fermi Kondo model

TL;DR

This paper demonstrates an exact mapping of the Bose-Fermi Kondo model to the Caldeira-Leggett model, revealing an emergent Kosterlitz-Thouless quantum phase transition, and uses numerical methods to analyze critical behavior.

Contribution

It establishes a precise mapping between the Bose-Fermi Kondo model and the Caldeira-Leggett model, uncovering a quantum phase transition in the former.

Findings

Identification of an emergent Kosterlitz-Thouless transition

Exact mapping between BFKM and Caldeira-Leggett model

Numerical analysis of physical quantities near transition

Abstract

We show that the Bose-Fermi Kondo model (BFKM), which may find applicability both to certain dissipative mesoscopic qubit devices and to heavy fermion systems described by the Kondo lattice model, can be mapped exactly onto the Caldeira-Leggett model. This mapping requires an ohmic bosonic bath and an Ising-type coupling between the latter and the impurity spin. This allows us to conclude unambiguously that there is an emergent Kosterlitz-Thouless quantum phase transition in the BFKM with an ohmic bosonic bath. By applying a bosonic numerical renormalization group approach, we thoroughly probe physical quantities close to the quantum phase transition.