Spin dynamics of an individual Cr atom in a semiconductor quantum dot under optical excitation

Abstract

We studied the spin dynamics of a Cr atom incorporated in a II-VI semiconductor quantum dot using photon correlation techniques. We used recently developed singly Cr-doped CdTe/ZnTe quantum dots (A. Lafuente-Sampietro et al., [1]) to access the spin of an individual magnetic atom. Auto-correlation of the photons emitted by the quantum dot under continuous wave optical excitation reveals fluctuations of the localized spin with a timescale in the 10 ns range. Cross-correlation gives quantitative transfer time between Cr spin states. A calculation of the time dependence of the spin levels population in Cr-doped quantum dots shows that the observed spin dynamics is controlled by the exciton-Cr interaction. These measurements also provide a lower bound in the 20 ns range for the intrinsic Cr spin relaxation time.Diluted magnetic semiconductor systems combining high-quality nano-structures and the magnetic properties of transition metal elements are good candidates for the development of single spin nano-electronic devices [2]. Thanks to their expected long coherence time, localized spin of individual magnetic atoms in a semiconductor host are an interesting media for storing quantum information in the solid state. Optical probing and control of the spin of individual or pairs of magnetic atoms have been obtained in both II-VI [3][4][5][6][7] and III-V [8,9] semiconductors. The variety of magnetic transition elements that could be incorporated in semiconductors gives a large choice of electronic and nuclear spins as well as orbital momentum [10,11]. In this context, growth and optical addressing of II-VI semiconductor quantum dots (QDs) containing an individual Cr atom were achieved recently [1].Cr is incorporated in II-VI compounds as Cr 2+ ions carrying a localized electronic spin S = 2 and an orbital momentum L = 2 [12]. In addition, most of the Cr isotopes have no nuclear spin. In the presence of a large bi-axial strain, the ground state of the Cr is an orbital singlet with spin degeneracy 2S+1=5. The nonzero orbital momentum of Cr and spin-orbit coupling result in a large sensitivity of its spin to local strain. This large spin to strain coupling, at least two orders of magnitude larger than for magnetic elements without orbital momentum (NV centers in diamond [13,14], Mn atoms in II-VI semiconductors [15]) makes Cr a very promising spin qubit for the realization of hybrid spin-mechanical systems in which the motion of a microscopic mechanical oscillator would be coherently coupled to the spin state of a single atom [16]. Large spin to strain coupling also enhances the spin-phonon interaction ultimately responsible for the spin relaxation and decoherence of an isolated magnetic atom in a semiconductor matrix. A too large interaction with phonons could limit the prac- * lucien.besombes@grenoble.cnrs.fr tical use of Cr as a qubit and an investigation of the spin dynamics in Cr-doped QDs is required.We show here how we can use the statistics of the photons emitted by a Cr-doped QD to probe the dynamics of the magnet...

Direct determination of the zero-field splitting for a singleCo2+ion embedded in a CdTe/ZnTe quantum dot

“…Therefore, optical manipulation of a single magnetic ion spin is possible not only in classical systems with a single Mn 2+ ion in QDs with a relatively low energy gap, CdTe/ZnTe [2][3][4][5][6] and InAs/GaAs [7][8][9], but also in QDs with a higher-energy gap such as CdSe/ZnSe [1,[10][11][12] or in QD systems doped with impurities considered previously as killers of photoluminescence: Co 2+ [1], Fe 2+ [13,14], and Cr 2+ [15,16]. For all the systems studied so far it has been found that the ground state of the magnetic ion is significantly influenced by the local strain present in a quantum dot.…”

Magnetoacoustic Relaxation by Cr2+ Jahn–Teller Centers Revealed from Elastic Moduli

“…Recently a first‐principle study of the Cr 2+ ‐doped ZnSe has been published . Experimental studies revealed a ferromagnetic p ‐ d exchange in the valence band (in contrast to Mn, Co, and Fe centers, which exhibit antiferromagnetic exchange), and a large spin to strain coupling . The latter makes Cr very promising as a spin qubit for the realization of hybrid spin‐mechanical systems, in which the motion of a microscopic mechanical oscillator would be coherently coupled to the spin state of a single atom .…”

“…Typically ultrasound experiments deal with temperature dependences of the phase velocity or attenuation. But in view of possible application in quantum computing, magneto‐acoustic investigation is deemed to be important. We have performed such experiments in wurtzite CdSe:Cr 2+ , fluorite SrF 2 :Cr 2+ , and sphalerite ZnSe:Cr 2+ single crystals.…”

“…[1] Experimental studies revealed a ferromagnetic p-d exchange in the valence band (in contrast to Mn, Co, and Fe centers, which exhibit antiferromagnetic exchange [2] ), and a large spin to strain coupling. [3] The latter makes Cr very promising as a spin qubit for the realization of hybrid spin-mechanical systems, in which the motion of a microscopic mechanical oscillator would be coherently coupled to the spin state of a single atom. [4] As in the majority of systems with openshell impurities, ZnSe:Cr 2þ is subject to the Jahn-Teller effect (JTE) with specific local properties.…”

Single-Mode-Fiber-Based Mach-Zehnder Interferometer Setup for Correlation Measurements for Single CdTe/ZnTe Quantum Dots

“…In the meantime, the II-VI QD systems were brought to spotlight as a host for single transition metal dopants [7,8]. For example, a single Mn 2+ ion or Cr atom spin in a single CdTe/ZnTe QD was shown to undergo coherent evolution [9,10], which is important from the point of view of quantum information processing. Progress in the solotronics urged us to explore the issue of photon indistiguishability in the II-VI system.…”