# Readout of a dopant spin in the anisotropic quantum dot with a single magnetic ion

## TL;DR

This paper presents a method to accurately read out and control the spin of a magnetic ion in an anisotropic quantum dot, overcoming polarization complications caused by electron-hole exchange interactions, with experimental validation on CdSe/ZnSe quantum dots.

## Contribution

It introduces a novel approach to extract spin polarization of both excitons and magnetic dopants in anisotropic quantum dots, verified experimentally on CdSe/ZnSe with Fe$^{2+}$ ions.

## Key findings

- Achieved record high optical orientation efficiency of dopant spin.
- Developed a method to extract spin polarization despite anisotropic exchange effects.
- Validated the approach on CdSe/ZnSe quantum dots with single Fe$^{2+}$ ions.

## Abstract

Owing to exchange interaction between the exciton and magnetic ion, a quantum dot embedding a single magnetic ion is a great platform for optical control of individual spin. In particular, a quantum dot provides strong and sharp optical transitions, which give experimental access to spin states of an individual magnetic ion. We show, however, that physics of quantum dot excitons also complicate spin readout and optical spin manipulation in such a system. This is due to electron-hole exchange interaction in anisotropic quantum dots, which affects the polarization of the emission lines. One of the consequences is that the intensity of spectral lines in a single spectrum are not simply proportional to the population of various spin states of magnetic ion. In order to provide a solution of the above problem, we present a method of extracting both the spin polarisation degree of a neutral exciton and magnetic dopant inside a semiconductor quantum dot in an external magnetic field. Our approach is experimentally verified on a system of CdSe/ZnSe quantum dot containing a single Fe$^{2+}$ ion. Both the resonant and non-resonant excitation regimes are explored resulting in a record high optical orientation efficiency of dopant spin in the former case. The proposed solutions can be easily expanded to any other system of quantum dots containing magnetic dopants.