Coherent control of a semiconductor quantum dot ensemble

Abstract

Coherent control of semiconductor quantum dots (QDs) has been the subject of intensive research to be used as a key technology for quantum engineering. Such technologies require phase-sensitive coherent manipulation of excitations in a QD, which have been demonstrated extensively in single QD studies. However, practical applications require extending these experiments to an ensemble of QDs. The presence of unavoidable large inhomogeneity in semiconductor QDs has been detrimental to progress on this front. A particularly difficult problem has been to unambiguously demonstrate Rabi oscillations in an inhomogeneously broadened excitation. Nonlinear coherent spectroscopy techniques such as two-dimensional coherent spectroscopy (2DCS) have enabled studying homogeneous properties of an inhomogeneously broadened system. Here we present our work on studying coherent population evolution of excitation in a QD ensemble through an extension of the 2DCS technique inspired by the traditional pump-probe spectroscopy. We have used 2DCS to “probe” the frequency-resolved-exciton population generated through coherent interaction with an initial “pump” pulse in an ensemble of self-assembled InAs QDs. Our results revealed intricate interplay between exciton, trion and biexciton populations, detuning effects, and the dominant damping mechanism for Rabi oscillation in the strongly-driven regime. Along with the population dynamics measurements, these insights are relevant for optimizing properties of QDs for useful applications.