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

•Optical 2D spectroscopy is implemented to study an InAs quantum dot ensemble.•Exchange-mediated splitting of bright excitons is measured with 30 neV resolution.•With increasing emission energy, the splitting decreases at a rate of 0.1μeV/meV.•Pure dephasing broadens the interband exciton linewidths beyond the radiative limit.•The two lowest-energy exciton states exhibit nearly perfectly correlated dephasing.

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 0.1μeV/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.