Optical Manipulation of a Single Mn Spin in a CdTe-Based Quantum Dot

Two coupled CdTe quantum dots, selected from a self-assembled system, one of them containing a single Mn ion, were studied by continuous wave and modulated photoluminescence, photoluminescence excitation, and photon correlation experiments. Optical writing of information on the spin state of the Mn ion has been demonstrated, using the orientation of the Mn spin by spin-polarized carriers transferred from the neighboring quantum dot. Mn spin orientation time values from 20 to 100 ns were measured, depending on the excitation power. Storage time of the information on the Mn spin was found to be enhanced by application of a static magnetic field of 1 T, reaching hundreds of microseconds in the dark. Simple rate equation models were found to describe correctly the static and dynamical properties of the system.

Figure 1

(a) Photoluminescence spectrum of a single QD with a single Mn ion, excited by linear polarization with indicated features related to neutral exciton ($X$), biexciton ($XX$), and charged excitons ($CX$). (b) Photoluminescence excitation map (density plot of PL intensity versus excitation/emission photon energy) close to the resonance. Inset: Schematic diagram of the relative position of the absorbing (smaller) and the emitting (larger, containing Mn ion) QD.

Figure 2

(a)–(d) Photoluminescence spectra excited at the resonance, using indicated excitation-detection polarizations. Measurements taken at $T=1.5\mathrm{K}$, and $B=0\mathrm{T}$ (a),(b) or $B=1\mathrm{T}$ (c),(d). (e) The mean spin of the Mn ion as a function of excitation power for $B=0$ and $B=1\mathrm{T}$ compared with model described in text (solid line). The arrow indicates the power at which averaged time delay between capture of two excitons (${\tau }_X$) is equal to 5 ns.

Figure 3

(a) Temporal profile of the PL intensity at one of the six components of the exciton spectrum (indicated in inset) during the excitation sequence described in text for $B=1\mathrm{T}$ and indicated values of excitation power. The horizontal arrow indicates the ratio between PL intensity measured in copolarization and cross-polarization setup at excitation power equal to $6\mu \mathrm{W}$. (b) PL intensity after turning on the excitation in ${\sigma }^{-}$ polarization versus length of dark period. (c) The Mn reorientation time upon illumination in ${\sigma }^{-}$ polarization (${\tau }_r$) versus averaged time delay between capture of two excitons (${\tau }_X$) and excitation power.