  The Zeeman-split spin states of a single quantum dot can be used together
with its optical trion transitions to form a spin-photon interface between a
stationary (the spin) and a flying (the photon) quantum bit. Besides long
coherence times of the spin state itself, the limiting decoherence mechanisms
of the trion states are of central importance. We investigate here in
time-resolved resonance fluorescence the electron and trion dynamics in a
single self-assembled quantum dot in an applied magnetic field of up to $B =
10\,$T. The quantum dot is only weakly coupled to an electron reservoir with
tunneling rates of about $1\,$ms$^{-1}$. Using this sample structure, we can
measure, in addition to the spin-flip rate of the electron and the spin-flip
Raman rate of the trion transition, the Auger recombination process, that
scatters an Auger electron into the conduction band. The Auger effect destroys
the radiative trion transition and leaves the quantum dot empty until an
electron tunnels from the reservoir into the dot. The Auger recombination rate
decreases by a factor of three from $\gamma_A=3\,\mu$s$^{-1}$ down to
$1\,\mu$s$^{-1}$ in an applied magnetic field of $10\,$T in Faraday geometry.
The combination of an Auger recombination event with subsequent electron
tunneling from the reservoir can flip the electron spin and thus constitutes a
previously unaccounted mechanism that limits spin coherence, an important
resource for quantum technologies.
