  We propose an all optical spin initialization and readout concept for single
self assembled quantum dots and demonstrate its feasibility. Our approach is
based on a gateable single dot photodiode structure that can be switched
between charge and readout mode. After optical electron generation and storage,
we propose to employ a spin-conditional absorption of a circularly polarized
light pulse tuned to the single negatively charged exciton transition to
convert the spin information of the resident electron to charge occupancy.
Switching the device to the charge readout mode then allows us to probe the
charge state of the quantum dot (1e, 2e) using non-resonant luminescence. The
spin orientation of the resident electron is then reflected by the
photoluminescence yield of doubly and singly charged transitions in the quantum
dot. To verify the feasibility of this spin readout concept, we have applied
time gated photoluminescence to confirm that selective optical charging and
efficient non perturbative measurement of the charge state can be performed on
the same dot. The results show that, by switching the electric field in the
vicinity of the quantum dot, the charging rate can be switched between a regime
of efficient electron generation and a readout regime, where the charge
occupancy and, therefore, the spin state of the dot can be tested via PL over
millisecond timescales, without altering it.
