Optical Stark Effect and Dressed Exciton States in a Mn-Doped CdTe Quantum Dot

Abstract

We report on the observation of spin dependent optically dressed states and optical Stark effect on an individual Mn spin in a semiconductor quantum dot. The vacuum-to-exciton or the excitonto-biexciton transitions in a Mn-doped quantum dot are optically dressed by a strong laser field and the resulting spectral signature is measured in photoluminescence. We demonstrate that the energy of any spin state of a Mn atom can be independently tuned using the optical Stark effect induced by a control laser. High resolution spectroscopy reveals a power, polarization and detuning dependent Autler-Townes splitting of each optical transition of the Mn-doped quantum dot. This experiment demonstrates a complete optical resonant control of the exciton-Mn system.Semiconductor quantum dots (QDs) exhibit discrete excitonic energy levels with an atom-like light-matter interaction. Resonant optical excitation of QDs has allowed to observe the absorption of a single QD [1] and the efficient preparation of the quantum state of a single confined carrier [2,3] It has also been demonstrated that the optical Stark effect can be used to compensate the exchange splitting in anisotropic QDs to produce entangled photon pairs [10].We show in this letter that the energy of any spin state of an individual Mn atom embedded in a II-VI semiconductor QD, can be tuned using the optical Stark effect induced by a strong laser field. Under resonant excitation, hybrid light-matter states are created independently for all Mn spin states. The corresponding Rabi energy measured through the Autler-Townes splitting can reach 250 µeV . At low temperature, the energies that control the dynamics of an isolated Mn spin in a CdTe QD, like the strain induced magnetic anisotropy or hyperfine coupling to the nuclei, are weaker than the observed optical Stark shifts. This opens a way to control the dynamics of a single Mn spin in its solid state environment. We also report optical Stark shifts and optically dressed states of the Mn exchanged coupled with the exciton or biexciton. Finally, we discuss a particular situation where two Mn spin states are mixed by the coupling between bright and dark excitons. In spite of the Mn spin mixing, we show that an optical manipulation of individual spin states can be performed.The sample used in this study is grown on a ZnTe substrate and contains CdTe QDs. A 6.5 monolayer thick CdTe layer is deposited at 280 • C by atomic layer epitaxy on a ZnTe barrier grown by molecular beam epitaxy at 360 • C. The dots are formed by a Tellurium deposition/desorption process [11] and protected by a 100 nm thick ZnTe top barrier. The QDs are 10-20 nm wide and few nm high. Mn atoms are introduced during the growth of the CdTe layer. The Mn concentration is adjusted to optimize the probability to detect one Mn per dot.Optical addressing of QDs containing a single magnetic atom is achieved using micro-spectroscopy techniques. A high refractive index hemispherical solid immersion lens is mounted on the surface of the sample to enhance the spatia...

Spin dynamics of a Mn atom in a semiconductor quantum dot under resonant optical excitation

“…The coupling with a resonant laser field can be used to tune the energy of one selected Mn spin state across the full fine structure of the Mn atom 13 . This allows in particular to restore the degeneracy of two consecutive Mn spins states giving an optical way to control the flipflops of the electronic and nuclear spins.…”

“…This crystal field splits the spin states of the Mn according to D 0 S 2 z . We demonstrated recently the possibility to tune this fine structure using the optical Stark effect 13 . Under strong resonant excitation of a Mndoped QD optical transition, optically dressed states of the Mn atom are created.…”

“…In the case of a singly Mn-doped QD, this leads to a splitting of the once simple photoluminescence (PL) spectrum of an individual QD into six (2S+1) components 11,15,16 . Since the confined carriers and Mn spin wave functions become strongly mixed, the optical excitation of the QD affects the spin state of the Mn through the exchange interaction offering a possibility of optical control 4,13,[17][18][19][20] .…”

“…The Autler-Townes effect in the fine structure of a neutral or charged QD 7,8 , the Mollow absorption spectrum of an individual QD 9 and the emission of an optically dressed exciton and biexciton complex 10 have been reported. In magnetic QDs containing an individual Mn atom 11,12 , it has been recently demonstrated that the energy of any spin state of a Mn can be tuned using the optical Stark effect induced by a strong laser field 13 . We present here a new way to exploit this coupling with a resonant laser field to initialize the spin of a magnetic atom inserted in a self-assembled QD.…”

Resonant photoluminescence and dynamics of a hybrid Mn hole spin in a positively charged magnetic quantum dot

“…Semiconductor quantum dots (QDs) permit efficient electrical or optical manipulation of individual carrier spins [6][7][8][9] . It has been shown that the optical properties of a QD can also be used to control the spin state of individual [10][11][12][13][14][15] or pairs 16,17 of magnetic atoms. The spin of a 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 [18][19][20] .…”