Direct measurement of spin dynamics in InAs/GaAs quantum dots using time-resolved resonance fluorescence

We temporally resolve the resonance fluorescence from an electron spin confined to a single self-assembled quantum dot to measure directly the spin's optical initialization and natural relaxation time scales at 4 K. Our measurements demonstrate that spin initialization occurs on the order of microseconds in the Faraday configuration when a laser resonantly drives the quantum dot transition. We show that the mechanism mediating the optically induced spin-flip changes from electron-nuclei interaction to hole-mixing interaction at 0.6 T external magnetic field. Spin relaxation measurements result in times on the order of milliseconds and suggest that a B-5 magnetic field dependence, due to spin-orbit coupling, is sustained all the way down to 2.2 T.