Impact of phonons on dephasing of individual excitons in deterministic quantum dot microlenses

TL;DR

This study investigates how phonons influence the dephasing of excitons in quantum dots, combining advanced fabrication, spectroscopy, and theoretical modeling to understand coherence loss mechanisms at low temperatures.

Contribution

It introduces a deterministic fabrication method for quantum dot microlenses and combines experimental and theoretical approaches to analyze phonon-induced dephasing.

Findings

Phonons cause initial coherence decay within picoseconds.

The zero-phonon line fraction is explained by the independent boson model.

The phonon-assisted photoluminescence lineshape matches theoretical predictions.

Abstract

Optimized light-matter coupling in semiconductor nanostructures is a key to understand their optical properties and can be enabled by advanced fabrication techniques. Using in-situ electron beam lithography combined with a low-temperature cathodoluminescence imaging, we deterministically fabricate microlenses above selected InAs quantum dots (QDs) achieving their efficient coupling to the external light field. This enables to perform four-wave mixing micro-spectroscopy of single QD excitons, revealing the exciton population and coherence dynamics. We infer the temperature dependence of the dephasing in order to address the impact of phonons on the decoherence of confined excitons. The loss of the coherence over the first picoseconds is associated with the emission of a phonon wave packet, also governing the phonon background in photoluminescence (PL) spectra. Using theory based on the independent boson model, we consistently explain the initial coherence decay, the zero-phonon line fraction, and the lineshape of the phonon-assisted PL using realistic quantum dot geometries.