Dynamics of the sub-Ohmic spin-boson model: a time-dependent variational study

TL;DR

This study uses a time-dependent variational method with the Davydov D1 ansatz to explore how initial conditions affect the dynamics and coherence in the sub-Ohmic spin-boson model, revealing a coherence transition at strong coupling.

Contribution

It demonstrates the effectiveness of the Dirac-Frenkel variational approach with the Davydov D1 ansatz in modeling sub-Ohmic spin-boson dynamics and highlights the impact of initial conditions on quantum coherence.

Findings

Quantum coherence survives under polarized bath initial condition even at strong coupling.

A coherence-incoherence transition occurs at alpha ~ 0.1 for s=0.25 with factorized bath initial condition.

The variational approach remains accurate for strong dissipation and deep sub-Ohmic baths.

Abstract

The Dirac-Frenkel time-dependent variation is employed to probe the dynamics of the zero temperature sub-Ohmic spin-boson model with strong friction utilizing the Davydov D1 ansatz. It is shown that initial conditions of the phonon bath have considerable influence on the dynamics. Counterintuitively, even in the very strong coupling regime, quantum coherence features still manage to survive under the polarized bath initial condition, while such features are absent under the factorized bath initial condition. In addition, a coherent-incoherent transition is found at a critical coupling strength alpha ~ 0.1 for s=0.25 under the factorized bath initial condition. We quantify how faithfully our ansatz follows the Schr\"{o}dinger equation, finding that the time-dependent variational approach is robust for strong dissipation and deep sub-Ohmic baths (s<<1).