Optical probing of the spin state of a single magnetic impurity in a self-assembled quantum dot

Optical spectra of a self-organized quantum dot with a single magnetic impurity are studied. The quantum dot potential and exchange interactions result in an additional fine structure of an exciton localized in a quantum dot with a magnetic impurity. In contrast to the undoped quantum dots, the ground state excitons in the quantum dot with a magnetic impurity are bright. It is also shown that an initial spin state of the $\mathrm{Mn}$ atom leaves a unique pattern in the optical response. This suggests the possibility to read out optically the spin polarization of a single $\mathrm{Mn}$ atom.

Figure 1

(a) Schematics of the optical absorption process. (b) Optical transitions in the system induced by the ${\sigma }_{+}$ photon.

Figure 2

(a) Geometry of an asymmetric quantum dot with a $\mathrm{Mn}$ impurity. (b) The lowest states of an exciton in a dot with $\mathrm{Mn}$ impurity. (c) Calculated PL spectrum; the width of Lorentzian peaks is $30\mu \mathrm{eV}$; for typical self-assembled $\mathrm{InGaAs}∕\mathrm{GaAs}$ QDs, $E_g^0$ is about $1\mathrm{eV}$. 

Figure 3

Absorption spectra for different initial $\mathrm{Mn}$ states $I_z$ of the $A^{-}$ impurity; the photon circular polarization is ${\sigma }_{+}$. The absorption for the initial $\mathrm{Mn}$ states with $I_z=+3∕2$ and $+5∕2$ is zero. The lowest panel presents the absorption spectrum of the $\mathrm{Mn}$ atom with a randomized spin in the initial state. For the broadening of the peaks we take $30\mu \mathrm{eV}$.

Figure 4

Absorption spectra of the $A^{-}$ impurity in a QD for two different initial spin distribution functions, $P_1\left(I_z\right)$ and $P_2\left(I_z\right)$; the polarization if incident photons is ${\sigma }_{+}$.