High-fidelity optical preparation and coherent Larmor precession of a single hole in an (In,Ga)As quantum dot molecule

We employ ultrafast pump-probe spectroscopy with photocurrent readout to directly probe the dynamics of a single hole spin in a single, electrically tunable self-assembled quantum dot molecule formed by vertically stacking (In,Ga)As quantum dots. Excitons with defined spin configurations are initialized in one of the two dots using circularly polarized picosecond pulses. The time-dependent spin configuration is probed by the spin selective optical absorption of the resulting few fermion complex. Taking advantage of sub-5 ps electron tunneling to an orbitally excited state of the other dot, we initialize a single hole spin with a purity of >96%, i.e., much higher than demonstrated in previous single dot experiments. Measurements in a lateral magnetic field monitor the coherent Larmor precession of the single hole spin with no observable loss of spin coherence within the ∼300 ps hole lifetime. Thereby, the purity of the hole spin initialization remains unchanged for all investigated magnetic fields.