International audienceWe demonstrate the optical addressability of the spin of an individual chromium atom (Cr) embedded in a semiconductor quantum dot. The emission of Cr-doped quantum dots and their evolution in magnetic field reveal a large magnetic anisotropy of the Cr spin induced by local strain. This results in the zero field splitting of the 0, ±1, and ±2 Cr spin states and in a thermalization on the magnetic ground states 0 and ±1. The observed strong spin to strain coupling of Cr is of particular interest for the development of hybrid spin-mechanical devices where coherent mechanical driving of an individual spin in an oscillator is needed. The magneto-optical properties of Cr-doped quantum dots are modeled by a spin Hamiltonian including the sensitivity of the Cr spin to the strain and the influence of the quantum dot symmetry on the carrier-Cr spin coupling

We report on the coherent dynamics of the spin of an individual magnetic atom coupled to carriers in a semiconductor quantum dot which has been investigated by resonant photoluminescence of the positively charged exciton (X + ). We demonstrate that a positively charged CdTe/ZnTe quantum dot doped with a single Mn atom forms an ensemble of optical Λ systems which can be addressed independently. We show that the spin dynamics of the X + -Mn complex is dominated by the electronMn exchange interaction and report on the coherent dynamics of the electron-Mn spin system that is directly observed in the time domain. Quantum beats reflecting the coherent transfer of population between electron-Mn spin states, which are mixed by an anisotropic strain in the plane of the quantum dot, are clearly observed. We finally highlight that this strain induced coherent coupling is tunable with an external magnetic field.Semiconductor quantum dots (QDs) are solid-state systems which permit efficient manipulation of single charge and spin. The optical properties of a QD can be used to control the spin state of carriers, nuclei as well as individual 1-4 or pairs 5,6 of magnetic atoms. The spin of one magnetic atom in a QD can be prepared by the injection of spin polarized carriers and its state can be read through the energy and polarization of the photons emitted by the QD. The insertion of a magnetic atom in a QD where the charge and strain states can be controlled offers additional degrees of freedom to tune the properties of the localized spin. Development of information processing using the spin of magnetic atoms in semiconductors will require tuning the coherent coupling between two or more spins. Controlling the exchange coupling of magnetic atoms with the spin of a carrier is an attractive approach to coherently transfer information between the atomic localized spins.Here we report on the coherent dynamics of the spin of a magnetic atom coupled to the spin of individual carriers. This dynamics has been investigated by resonant photoluminescence (PL) of the positively charged exciton (X + ) coupled to a single Mn in a p-doped CdTe/ZnTe QD 7 . We have analysed the spin dynamics of the X + -Mn complex under resonant excitation and show that it is controlled by the electron-Mn (e-Mn) interaction. We demonstrate that a positively charged Mn-doped QD forms optical Λ systems that can be addressed with resonant lasers. We show that the coherent dynamics of the coupled electron and Mn spins is extremely sensitive to the local strain at the Mn location. Oscillations in the circular polarization rate of the resonant PL reveal quantum beats between e-Mn spin states mixed by an anisotropic strain in the plane of the QD. This coherent coupling, characterized by a change in the angular momentum ∆S z = ±2, can be tuned by a magnetic field.The sample consist of Mn-doped CdTe QDs grown by molecular beam epitaxy on a p-doped ZnTe(001) substrate 8 . A positive bias voltage is applied between a 6 nm thick gold semi-transparent Schottcky gate deposi...