Correlation and dephasing effects on the non-radiative coherence between bright excitons in an InAs QD ensemble measured with 2D spectroscopy

TL;DR

This study investigates how exchange interactions and dephasing influence the non-radiative coherence of bright excitons in InAs quantum dots using 2D spectroscopy, revealing energy-dependent splitting and coherence protection mechanisms.

Contribution

It provides new insights into the correlation between fine-structure splitting and emission energy, and the role of pure dephasing in exciton coherence decay in quantum dot ensembles.

Findings

Fine-structure splitting decreases with increasing emission energy at 0.1 μeV/meV.

Pure dephasing causes exciton coherence to decay faster than the radiative limit at low temperature.

Bright state transition energy fluctuations are nearly perfectly correlated, protecting coherence.

Abstract

Exchange-mediated fine-structure splitting of bright excitons in an ensemble of InAs quantum dots is studied using optical two-dimensional Fourier-transform spectroscopy. By monitoring the non-radiative coherence between the bright states, we find that the fine-structure splitting decreases with increasing exciton emission energy at a rate of 0.1 $\mu$eV/meV. Dephasing rates are compared to population decay rates to reveal that pure dephasing causes the exciton optical coherences to decay faster than the radiative limit at low temperature, independent of excitation density. Fluctuations of the bright state transition energies are nearly perfectly-correlated, protecting the non-radiative coherence from interband dephasing mechanisms.