Three-photon excitation of quantum two-level systems

TL;DR

This paper demonstrates efficient three-photon excitation of semiconductor quantum dots, enabling direct measurement of exciton radiative lifetimes and improved polarization properties, with theoretical modeling confirming the process's underlying physics.

Contribution

It introduces a resonant three-photon excitation technique for quantum dots, supported by Floquet theory modeling, offering new insights into their intrinsic properties.

Findings

Efficient three-photon excitation observed in quantum dots.

Direct measurement of exciton radiative lifetime achieved.

Enhanced linear polarization in emission without filtering.

Abstract

We demonstrate that semiconductor quantum dots can be excited efficiently in a resonant three-photon process, whilst resonant two-photon excitation is highly suppressed. Time-dependent Floquet theory is used to quantify the strength of the multi-photon processes and model the experimental results. The efficiency of these transitions can be drawn directly from parity considerations in the electron and hole wavefunctions in semiconductor quantum dots. Finally, we exploit this technique to probe intrinsic properties of InGaN quantum dots. In contrast to non-resonant excitation, slow relaxation of charge carriers is avoided which allows us to measure directly the radiative lifetime of the lowest energy exciton states. Since the emission energy is detuned far from the resonant driving laser field, polarization filtering is not required and emission with a greater degree of linear polarization is observed compared to non-resonant excitation.