  In a radiative Auger process, optical decay is accompanied by simultaneous
excitation of other carriers. The radiative Auger process gives rise to weak
red-shifted satellite peaks in the optical emission spectrum. These satellite
peaks have been observed over a large spectral range: in the X-ray emission of
atoms; close to visible frequencies on donors in semiconductors and quantum
emitters; and at infrared frequencies as shake-up lines in two-dimensional
systems. So far, all the work on the radiative Auger process has focussed on
detecting the spontaneous emission. However, the fact that the radiative Auger
process leads to photon emission suggests that the transition can also be
optically excited. In such an inverted radiative Auger process, excitation
would correspond to simultaneous photon absorption and electronic
de-excitation. Here, we demonstrate optical driving of the radiative Auger
transition on a trion in a semiconductor quantum dot. The radiative Auger and
the fundamental transition together form a $\Lambda$-system. On driving both
transitions of this $\Lambda$-system simultaneously, we observe a reduction of
the fluorescence signal by up to $70\%$. Our results demonstrate a type of
optically addressable transition connecting few-body Coulomb interactions to
quantum optics. The results open up the possibility of carrying out THz
spectroscopy on single quantum emitters with all the benefits of optics:
coherent laser sources, efficient and fast single-photon detectors. In analogy
to optical control of an electron spin, the $\Lambda$-system between the
radiative Auger and the fundamental transitions allows optical control of the
emitters' orbital degree of freedom.
