  Coherent control of individual two-level systems (TLSs) is at the basis of
any implementation of quantum information. An impressive level of control is
now achieved using nuclear, vacancies and charge spins. Manipulation of bright
exciton transitions in semiconductor quantum dots (QDs) is less advanced,
principally due to the sub-nanosecond dephasing. Conversely, owing to their
robust coupling to light, one can apply tools of nonlinear spectroscopy to
achieve all-optical command. Here, we report on the coherent manipulation of an
exciton via multi-wave mixing. Specifically, we employ three resonant pulses
driving a single InAs QD. The first two induce a four-wave mixing (FWM)
transient, which is projected onto a six-wave mixing (SWM) depending on the
delay and area of the third pulse, in agreement with analytical predictions.
Such a switch enables to demonstrate the generation of SWM on a single emitter
and to engineer the spectro-temporal shape of the coherent response originating
from a TLS. These results pave the way toward multi-pulse manipulations of
solid state qubits via implementing the NMR-like control schemes in the optical
domain.
