Dynamics of excitons in individual InAs quantum dots revealed in four-wave mixing spectroscopy

A detailed understanding of the population and coherence dynamics in optically driven individual emitters in solids and their signatures in ultrafast nonlinear optical signals is of prime importance for their applications in future quantum and optical technologies. In a combined experimental and theoretical study on exciton complexes in single semiconductor quantum dots, we reveal a detailed picture of the dynamics by employing three-beam polarization-resolved four-wave mixing (FWM) micro-spectroscopy. The oscillatory dynamics of the FWM signals in the exciton-biexciton system is governed by the fine-structure splitting and the biexciton binding energy. There is an excellent quantitative agreement between the measurement and analytical description. The analysis of the excitation conditions exhibits a dependence of the dynamics on the specific choice of polarization configuration, pulse areas, and temporal ordering of driving fields. The interplay between the transitions in the four-level exciton system leads to the rich evolution of the coherence and population. Using two-dimensional FWM spectroscopy, we elucidate the exciton-biexciton coupling and identify neutral and charged exciton complexes in a single quantum dot. Our investigations thus clearly reveal that FWM spectroscopy is a powerful tool to characterize the spectral and dynamical properties of single quantum structures. (C) 2016 Optical Society of America