Optical properties of a semiconductor quantum dot with a single magnetic impurity: photoinduced spin orientation

Abstract

We describe the optical resonant manipulation of a single magnetic impurity in a self-assembled quantum dot. We show that using the resonant pumping one can address and manipulate selectively individual spin states of a magnetic impurity. The mechanisms of resonant optical polarization of a single impurity in a quantum dot involve anisotropic exchange interactions and are different to those in diluted semiconductors. A Mn impurity can act as qubit. The limiting factors for the qubit manipulation are the electron-hole exchange interaction and finite temperature. The spins of electrons in semiconductors strongly couple with electric and magnetic fields due to the spin-orbit and exchange interactions. Spintronics and quantum computation utilize these interactions to manipulate the electron spins 1,2. One important class of spintronics materials is diluted magnetic semiconductors 3 which combine high-quality semiconductor structures with magnetic properties of impurities. Since many semiconductors efficiently emit and absorb light, the spin states of electrons and magnetic impurities can be manipulated optically by using circularly-polarized light pulses 4. In diluted magnetic semiconductors such as bulk crystals, quantum wells and dots, photo-generated excitons interact with a large collection of spins of Mn impurities and therefore a large number of degrees of freedom becomes involved 5,6,7,8,9,10,11. In these systems, it is challenging to address individual spins of Mn atoms. At the same time, the quantum computational schemes are based on qubits, pairs of well-controlled quantum states. These elementary blocks, qubits, should be made interacting or decou-pled on demand. In a diluted magnetic semiconductor, even a single Mn atom has 6 spin states (I Mn = 5/3). Therefore, 15 different pairs of states (qubits) can be defined for a single Mn impurity. Here we study a system which allows us to manipulate optically a single Mn spin. This system is composed of a quantum dot (QD) and a single Mn impurity. Note that the optical properties of a QD with a single Mn impurity were recently discussed in refs. 12,13. This letter describes a single Mn impurity embedded into a self-assembled QD. Importantly, such a system permits efficient selective optical control and manipulation of individual spin states and defining a single qubit for the Mn impurity. This ability comes from the exciton spectrum of a QD with a Mn atom. An exciton in a QD has a well-defined discrete spectrum and, simultaneously , strongly interacts with the Mn spin via the exchange interaction. Since the exciton and Mn spin functions become strongly mixed, the resonant optical exci-tation strongly affect the spin state of Mn impurity. In particularly, we show that one can write spin states of Mn atom. Since spin relaxation of paramagnetic ions in the absence of carriers (i.e. after the exciton recombina-tion) is an extremely slow process (∼ 10 µs), a single Mn spin is a very promising candidate for spintronics applications. The mechanisms of Mn-spin polarizat...

Electrical Control of a Single Mn Atom in a Quantum Dot

“…The PL emission pattern of the charged excitons differs strongly from that of the neutral exciton. This difference reflects the fact that the Mn spin is very sensitive to the number of electrons and holes in both the excited and the ground states of the optical transitions [11,12].…”

“…The PL emission pattern of the charged excitons differs strongly from that of the neutral exciton. This difference reflects the fact that the Mn spin is very sensitive to the number of electrons and holes in both the excited and the ground states of the optical transitions [11,12].Micro-spectroscopy was used to study the magnetooptical properties of self-assembled CdTe=ZnTe QDs doped with single Mn atoms. A low density of Mn atoms is introduced in the QD plane exploiting the Mn diffusion through a ZnTe spacer layer grown on a ZnMnTe barrier [4,17].…”

Single-exciton spectroscopy of single Mn doped InAs quantum dots

“…Quantum dots doped with a single magnetic atom are a model system for nanospintronics. [9][10][11] These systems can also be used as a reference to interpret the experiments on Mn doped nanocrystals. 12,13 The focus of this work is the single exciton spectroscopy of a single Mn atom in a InAs quantum dot ͑QD͒, motivated by recent experimental results on InAs QD ͑Ref.…”

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

“…The transition rates Γ γ→γ ′ between the different Mnhole states depend on their energy separation 53 . This accounts for a thermalization among the 12 Mn-hole levels with an effective spin temperature T .…”