Uncovering nonperturbative dynamics of the biased sub-Ohmic spin-boson model with variational Matrix Product States

TL;DR

This paper investigates the complex nonperturbative dynamics of the biased sub-Ohmic spin-boson model using a time-dependent variational matrix product state approach, revealing diverse regimes from damped oscillations to spin freezing.

Contribution

It introduces a TDVMPS method to study the nonperturbative dynamics of the biased sub-Ohmic spin-boson model across different coupling regimes, including intermediate.

Findings

Weak coupling shows damped spin oscillations

Strong coupling results in spin freezing near initial state

Intermediate coupling exhibits combined dynamic features

Abstract

We study the dynamics of the biased sub-Ohmic spin-boson model by means of a time-dependent variational matrix product state (TDVMPS) algorithm. The evolution of both the system and the environment is obtained in the weak- and the strong-coupling regimes, respectively characterized by damped spin oscillations and by a nonequilibrium process where the spin freezes near its initial state, which are explicitly shown to arise from a variety of reactive environmental quantum dynamics. We also explore the rich phenomenology of the intermediate-coupling case, a nonperturbative regime where the system shows a complex dynamical behavior, combining features of both the weakly and the strongly coupled case in a sequential, time-retarded fashion. Our work demonstrates the potential of TDVMPS methods for exploring otherwise elusive, nonperturbative regimes of complex open quantum systems, and points to the possibilities of exploiting the qualitative, real-time modification of quantum properties induced by nonequilibrium bath dynamics in ultrafast transient processes.