electrons in semiconductor nanostructures.

![image](fig1c){width="1.8\columnwidth"}

We resonantly excite the negative trion ($X^{1-}$) of a QD with a narrow-bandwidth laser. In both QD systems, the charge state of the QD is precisely controlled via Coulomb blockade [@Warburton2000]. We collect the emission of the QD and resolve it spectrally, as schematically shown in Fig. \[fig:mechanism\](a). Shown in Fig. \[fig:mechanism\](b) is the result of such a measurement for an InGaAs QD. The main peak at photon energy $\sim1.321\ \text{eV}$ is the resonance fluorescence of the trion. This spectrally narrow emission is accompanied by an LA-phonon sideband on the red side [@Hansom2014b; @Koong2019; @Brash2019]. The crucial observation we report here is the appearance of two weak emission lines, red-shifted by $\sim17\ \text{meV}$ from the main fluorescence peak. We show that these emission lines originate from a radiative Auger process, which is illustrated in Fig. \[fig:mechanism\](c): an electron and a hole recombine optically and with a small probability, the second electron is promoted to an excited state, the $p$-shell of the QD. In the case of resonance fluorescence, in contrast, the optical recombination of the trion leaves behind a single electron in the ground state ($s$-shell of the QD).

![image](fig2e){width="1.8\columnwidth"}

In the following, we prove 