Abstract
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 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 in an excellent quantitative agreement between 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 rich evolution of 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 spectral and dynamical properties of single quantum structures.
Highlights
A comprehensive understanding of exciton complexes and their transitions in semiconductor quantum dots (QDs) is a crucial step for assessing their functionality as optically controllable solid state devices in quantum information technology [1,2,3]
In this paper we present a comprehensive set of measurements and simulations, exploring the oscillatory dynamics of coherences and populations in the exciton-biexciton system in a single QD
We have presented a combined experimental and theoretical study on four-wave mixing (FWM) signals retrieved from single, stronglyconfined InAs QDs embedded in a low-Q semiconductor microcavity
Summary
A comprehensive understanding of exciton complexes and their transitions in semiconductor quantum dots (QDs) is a crucial step for assessing their functionality as optically controllable solid state devices in quantum information technology [1,2,3]. While FWM has often been used to infer exciton dynamics in QWs [16] or for QD ensembles [17], for single QDs the experiments are more challenging because of the weak signal intensity. This longstanding issue has recently been solved by exploiting photonic nanostructures to enhance non-linear responses. In 2D FWM spectra transitions correspond to peaks on the diagonal, while the coupling between different states can be seen by off-diagonal peaks connecting the diagonal ones [24,25,26] We show that this technique allows for a fast, comprehensive characterization of exciton complexes. We study 2D FWM maps identifying neutral and charged exciton complexes
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