transferred to the Auger electron. We show here that the radiative Auger effect is a powerful probe for single electrons: the energy separations between the resonance fluorescence and the radiative Auger emission directly measure the single-particle energies of the QD with a very high precision. In semiconductors, these single-particle energies are otherwise hard to access by optical means since particles are generally excited in pairs, as excitons. After the radiative Auger excitation, the Auger carrier relaxes back to the lowest shell of the confinement potential. With a quantum optics-based correlation measurement, we determine the rate corresponding to this single-particle relaxation in the absence of any other particles. Also this is typically hard to achieve by optical means: even for quasi-resonant $p$-shell excitation, electron relaxation takes place in the presence of a hole, which changes the relaxation dynamics.

We observe the radiative Auger process on two different systems: first, a self-assembled InGaAs QD in GaAs grown in the Stranski-Krastanov mode [@Michler2003] and second, a GaAs QD in AlGaAs grown by infilling of droplet-etched nano-holes [@Huo2013]. This system-independence strongly suggests that radiative Auger has general applicability: it allows precise, sensitive and fast optical techniques to determine the energies and dynamics of single 