Fig. 1: Radiative Auger emission and excitation of the radiative Auger transition.

a Schematic illustration of the fundamental transition and the radiative Auger process. The trion state \(\left|t\right\rangle\) optically decays by recombination of one electron in the conduction band (cb) with a hole in the valence band (vb). The second electron either stays in its ground state \(\left|s\right\rangle\) (fundamental transition), or is left in a higher shell \(\left|p\right\rangle\) (radiative Auger). The radiative Auger photon is red-shifted from the fundamental transition by the energy transferred to the Auger electron. b Emission spectrum from a negatively charged quantum dot upon optical excitation at the fundamental transition. In addition to the fundamental transition (highlighted in blue), there is a red-shifted satellite line (highlighted in red). This emission arises from the radiative Auger process, where the trion state \(\left|t\right\rangle\) decays to the excited electron state \(\left|p\right\rangle\). c Two possible absorption channels in the presence of one confined conduction band electron. When the electron is in the ground state \(\left|s\right\rangle\), a laser resonant with the fundamental transition (blue, frequency ω₁, Rabi frequency Ω₁) excites a valence band electron and brings the system to the trion state, \(\left|t\right\rangle\). When the conduction band electron is in an excited state \(\left|p\right\rangle\), a red-shifted laser (frequency ω₂, Rabi frequency Ω₂) can excite the system to the same trion state \(\left|t\right\rangle\). In this inverted radiative Auger process, the missing energy is provided by the excited electron. d Resonance fluorescence from the fundamental transition in the presence of a strong second laser. When the second laser (ω₂) is on resonance with the radiative Auger transition (Δ₂ = 0), the resonance fluorescence intensity is strongly reduced.