Ultrafast non-linear optical signal from a single quantum dot: exciton and biexciton effects

TL;DR

This paper investigates the ultrafast non-linear optical response of a single quantum dot, revealing biexciton effects, coherent oscillations, and non-Markovian dynamics on a subpicosecond timescale.

Contribution

It demonstrates the importance of exciton-exciton interactions and phase dynamics in the non-linear optical response of quantum dots, highlighting effects not captured by mean-field models.

Findings

Biexciton effects dominate the FWM signal at subpicosecond timescales.

Coherent oscillations in the FWM signal are observed, linked to biexciton binding energy.

Non-Markovian effects are evidenced through phase dynamics analysis.

Abstract

We present results on both the intensity and phase-dynamics of the transient non-linear optical response of a single quantum dot (SQD). The time evolution of the Four Wave Mixing (FWM) signal on a subpicosecond time scale is dominated by biexciton effects. In particular, for the cross-polarized excitation case a biexciton bound state is found. In this latter case, mean-field results are shown to give a poor description of the non-linear optical signal at small times. By properly treating exciton-exciton effects in a SQD, coherent oscillations in the FWM signal are clearly demonstrated. These oscillations, with a period corresponding to the inverse of the biexciton binding energy, are correlated with the phase dynamics of the system's polarization giving clear signatures of non-Markovian effects in the ultrafast regime.