The Hidden Phase of the Spin-Boson Model

TL;DR

This paper explores the complex nonequilibrium dynamics of a two-level quantum system in a sub-Ohmic environment, revealing a new aperiodic phase and mapping the phase diagram using advanced numerical methods.

Contribution

It introduces a new aperiodic phase in the spin-boson model's phase diagram and accurately determines phase boundaries using the time-evolving matrix product operator approach.

Findings

Identification of a new aperiodic phase at strong coupling

Mapping of the phase diagram including known and new phases

Demonstration of non-coherent dynamics slaved to bath oscillations

Abstract

A quantum two-level system immersed in a sub-Ohmic bath experiences enhanced low-frequency quantum statistical fluctuations which render the nonequilibrium quantum dynamics highly non-Markovian. Upon using the numerically exact time-evolving matrix product operator approach, we investigate the phase diagram of the polarization dynamics. In addition to the known phases of damped coherent oscillatory dynamics and overdamped decay, we identify a new third region in the phase diagram for strong coupling showing an aperiodic behaviour. We determine the corresponding phase boundaries. The dynamics of the quantum two-state system herein is not coherent by itself but slaved to the oscillatory bath dynamics.