A semiconductor quantum dot (QD) containing a single Mn atom is a promising system from the point of view
of future information processing and storage devices. An efficient optical read-out of the single Mn spin state in
a CdTe/ZnTe quantum dot, as well as studies of dynamics of this state, were recently reported by L. Besombes
and co-workers. However, to construct the building blocks of future memory devices basing on single magnetic
atoms the ability to control a single spin is still needed.
This work is focused on the advancement in writing and storing of information on the Mn spin state. We
demonstrate optical writing of information on the spin state of a single Mn ion embedded in a CdTe QD and we
test the storage time in the range of a few tenths of a millisecond. A spin-conserving excitation transfer between
two coupled QDs is used as a tool for optical manipulation of the Mn spin. Excitons resonantly created in a
dot without magnetic atom by circularly polarized light tunnel to the dot with the Mn ion in a few picoseconds.
Then they act on the Mn ion via the sp-d exchange interaction and orient its spin. The orientation is much
more efficient in presence of a magnetic field of about 1T, due to suppression of fast spin relaxation channels.
Dynamics of the Mn spin under polarized excitation as well as the information storage time on the Mn spin was
measured in a time-resolved experiment, in which the intensity and polarization of excitation were modulated.
Observed dynamics can be described with a simple rate equation model. The storage time was enhanced by the
magnetic field and reached about half a millisecond at 1T.
In this paper we describe the study of the magnetization dynamics after a short magnetic pulse, down to
zero field and with a temporal resolution of a few ns, in (Cd,Mn)Te QWs with 0.2% to 1.5% Mn, and various
densities of carriers. Short pulses of magnetic field were applied in the Faraday configuration by a small magnetic
coil mounted at the surface of the sample. We analyzed the temporal evolution of the giant Zeeman shift of
spectroscopic lines after the pulse with resolution down to a few nanoseconds. This evolution reproduces the
dynamics of the magnetization of the Mn system. The dynamics in absence of magnetic field was found to be up
to three orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for
this fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system
of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional
This work is devoted to correlation spectroscopy of individual II-VI CdTe/ZnTe QDs in view to determine non-resonant
excitation mechanisms and provide information on spin relaxation of QD states. Second order photon autocorrelations
and cross-correlations were measured in a Hanbury-Brown and Twiss setup for neutral and charged exciton and
biexciton transitions, excited by pulses of a frequency-doubled femtosecond Ti:Sapphire laser. Some of the
measurements were circular- or linear polarization resolved and performed in magnetic field. Besides, measurements of
photoluminescence excited by pairs of laser pulses revealed fast excitation phenomena in the range of tens of ps. The
results of measurements without polarization resolution were interpreted using a simple rate equation model and allowed
us to establish the dominant role of single carrier capture in the non-resonant excitation of the QD. Polarization-dependent
correlation measurements were used to study the magnetic field controlled transition between anisotropic QD
exciton eigenstates active in linear polarization and those active in circular polarization. The same measurements
provided information on spin relaxation of the carriers left in the dot after charged exciton recombination.