Open Wilson chains for quantum impurity models: Keeping track of all bath modes

TL;DR

This paper introduces open Wilson chains that incorporate all bath modes for quantum impurity models, improving accuracy and addressing issues like the mass-flow problem, especially in asymmetric spectral functions at finite temperature.

Contribution

The authors develop a systematic method to include all bath modes via open Wilson chains, enhancing the modeling of quantum impurity systems.

Findings

Successfully cure the mass-flow problem in impurity models

Observe flow towards Gaussian critical fixed point in spin-boson model

Demonstrate improved treatment of asymmetric bath spectral functions

Abstract

When constructing a Wilson chain to represent a quantum impurity model, the effects of truncated bath modes are neglected. We show that their influence can be kept track of systematically by constructing an "open Wilson chain" in which each site is coupled to a separate effective bath of its own. As a first application, we use the method to cure the so-called mass-flow problem that can arise when using standard Wilson chains to treat impurity models with asymmetric bath spectral functions at finite temperature. We demonstrate this for the strongly sub-Ohmic spin-boson model at quantum criticality where we directly observe the flow towards a Gaussian critical fixed point.