Quantum dot Rabi rotations beyond the weak exciton-phonon coupling regime

TL;DR

This paper develops an advanced theoretical model for quantum dot excitonic dynamics that surpasses the limitations of weak exciton-phonon coupling approximations, accurately capturing multiphonon effects and phonon-induced frequency renormalization.

Contribution

It introduces a combined polaron transform and time-local projection operator approach to model excitonic dynamics beyond weak coupling regimes, including non-Markovian effects.

Findings

Weak-coupling and polaron theories agree below 30 K

Discrepancies arise at higher temperatures due to multiphonon effects

Non-Markovian effects have minimal impact on Rabi rotations

Abstract

We study the excitonic dynamics of a driven quantum dot under the influence of a phonon environment, going beyond the weak exciton-phonon coupling approximation. By combining the polaron transform and time-local projection operator techniques we develop a master equation that can be valid over a much larger range of exciton-phonon coupling strengths and temperatures than the standard weak-coupling approach. For the experimentally relevant parameters considered here, we find that the weak-coupling and polaron theories give very similar predictions for low temperatures (below 30 K), while at higher temperatures we begin to see discrepancies between the two. This is due to the fact that, unlike the polaron approach, the weak-coupling theory is incapable of capturing multiphonon effects, while it also does not properly account for phonon-induced renormalisation of the driving frequency. In particular, we find that the weak-coupling theory often overestimates the damping rate when compared to that predicted by the polaron theory. Finally, we extend our theory to include non-Markovian effects and find that, for the parameters considered here, they have little bearing on the excitonic Rabi rotations when plotted as a function of pulse area.