Radiative Auger Process in the Single Photon Limit on a Quantum Dot.

In a multi-electron atom, an excited electron can decay by emitting a photon. Typically, the leftover electrons are in their ground state. In a radiative Auger process, the leftover electrons are in an excited state and a red-shifted photon is created. In a quantum dot, radiative Auger is predicted for charged excitons. For a singly-charged trion, a photon is created on electron-hole recombination, leaving behind a single electron. Radiative Auger determines the quantisation energies of this single electron, information which is otherwise difficult to acquire. For this reason, radiative Auger is a powerful tool. However, radiative Auger has not been observed on single quantum dots. Here, we report radiative Auger on trions in single quantum dots. There are sharp red-shifted emission lines with intensities as high as 1% of the main emission enabling the single-electron quantisation energies to be measured with high precision. Going beyond the original proposals, we show how quantum optics -- an analysis of the photon correlations -- gives access to the single-electron dynamics, notably relaxation and tunneling. All these properties of radiative Auger can be exploited on other semiconductor nanostructures and colour centres.