Optical control of the spin of a magnetic atom in a semiconductor quantum dot

The control of single spins in solids is a key but challenging step for any spin-based solid-state quantum-computing device. Thanks to their expected long coherence time, localized spins on magnetic atoms in a semiconductor host could be an interesting media to store quantum information in the solid state. Optical probing and control of the spin of individual or pairs of Mn atoms (S=5/2) have been obtained in II-VI and III-V semiconductor quantum dots during the last years. In this paper , we review recently developed optical control experiments of the spin of an individual Mn atoms in II-VI semiconductor self-assembled or strain free quantum dots. We first show that the fine structure of the Mn atom and especially a strained induced magnetic anisotropy is the main parameter controlling the spin memory of the magnetic atom at zero magnetic field. We then demonstrate that the energy of any spin state of a Mn atom or pairs of Mn atom can be independently tuned by using the optical Stark effect induced by a resonant laser field. The strong coupling with the resonant laser field modifies the Mn fine structure and consequently its dynamics. We then describe the spin dynamics of a Mn atom under this strong resonant optical excitation. In addition to standard optical pumping expected for a resonant excitation, we show that the Mn spin population can be trapped in the state which is resonantly excited. This effect is modeled considering the coherent spin dynamics of the coupled electronic and nuclear spin of the Mn atom optically dressed by a resonant laser field. Finally, we discuss the spin dynamics of a Mn atom in strain free quantum dots and show that these structures should permit a fast optical coherent control of an individual Mn spin.