Activity Report 2010 - CNRS

SCIENTIFIC REPORT
FURTHER READING:
[10] Phys. Rev. B 81, 245315 (2010).
Optical initialization, readout, and dynamics
of a Mn spin in a quantum dot
Semiconductor
quantum
dots
Chair of Excellence 2007: Joaquin
FERNANDEZ-ROSSIER
Coordinator: Henri MARIETTE (Institut
Néel).
Electron spins confined in quantum dots
(QDs) are one of the proposed physical
realizations for a qubit. The most studied
system is a QD defined by gating a 2D
electron gas in GaAs. Two original
systems based on self-assembled QDs
are studied within programs of the
Nanosciences Foundation: a single
magnetic impurity in a QD, and Si-Ge
QDs (see the Quantum Electronics
report).
Thanks to the strong spin-carrier
coupling, one can exploit the absorption
of an individual II-VI QD to optically
initialize the spin state of a single
magnetic impurity contained in the QD,
and to optically monitor its dynamics.
A new set-up involving resonant
excitation to achieve optical pumping of
the single quantum dot, with or without a
trapped carrier, allowed us to study the
dynamics of an isolated Mn spin, and the
effect of the Mn spin on the electron-hole
pair dynamics. For instance, when the Mn
spin is embedded in the strongly strained
QD, we observe a long spin lifetime in the
dark, and a short one in the presence of
an exciton, so that an efficient optical
pumping is achieved. Within the Chair of
Excellence, the full dynamics of the
coupled system has been modelled [10].
In a second step, the model is further
extended to encompass coherent
manipulation through optical Stark effect
or microwaves. This is a much more
complex experiment for which
preliminary results have been obtained
(Fig. 9).
Dissemination and Training
A user list has been established to
coordinate the conferences and seminars
held at the Institut Néel (CNRS),
Nanomagnétisme Laboratory (CEA/INAC)
and SPINTEC Laboratory (UMR
CEA/CNRS/UJF & Grenoble INP).
A two day colloquium “Nanomagnetism
and Spintronics” has been organized on
November, 24 th and 25 th 2010 with the
aim to present an overview on current
research in Rhône-Alpes and in France, in
Quebec and Canada, along with a
broader outline of cutting-edge research
on-going in other European research
centres.
Thesis Prize Laureate
Dimitri HOUSSAMEDDINE, one of the two
laureates of the 2010 Nanosciences
Foundation Thesis Prize, has deposited 3
patents and published 4 publications as
main author (in addition to 6 other
publications) during his thesis.
On December 2, 2010, in the frame of
the Prize Award Ceremony, his talk
entitled “Magnetization dynamics in spin
torque microwave nano-oscillators” has
illustrated the excellence of his results.
Fig. 9: Spin dependent optically dressed states
in a Mn-doped QD: TEM cross section of a QD
(left) and anticrossing due to the optical Stark
effect (right).
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