To explain the radiative Auger process, the Coulomb interactions between the carriers forming the trion must be considered. The radiative Auger process takes place because these interactions change the eigenfunctions of the system (see Supplement). In a single-particle basis, the initial state contains admixtures of Slater-determinants of higher single-particle shells. The optical recombination removes an electron-hole pair from the initial trion state, leading to a final state which is a superposition of single-electron single-particle states. Every state in that superposition consists of an electron in a particular shell along with a photon of a certain energy. Since the initial state is always the same, the energy separations between the different emission lines correspond to precise single-particle splittings. The ratio of radiative Auger emission and resonance fluorescence reflects the expansion of the trion state in single-particle states. Compared to the resonance fluorescence, the radiative Auger emission is weaker by about 2–3 orders of magnitude. The trion wavefunctions are close, yet not equal to, single-particle states.

In conclusion, we experimentally demonstrate that there is a radiative Auger process connected to the optical recombination of a trion in a single QD. The measurements are performed on two different types of semiconductor QDs. We 