# Antireflective photonic structure for coherent nonlinear spectroscopy of single magnetic quantum dots

## TL;DR

This paper demonstrates a photonic structure that enhances nonlinear spectroscopy of single magnetic quantum dots, enabling detailed studies of exciton coherence and spin interactions in a controlled environment.

## Contribution

It introduces a half-cavity photonic structure for coherent nonlinear spectroscopy of individual magnetic quantum dots, including measurements of exciton dephasing times and detection of magnetic dopants.

## Key findings

- Achieved resonant spectroscopy of single QDs with enhanced signal.
- Measured exciton dephasing time T2 ≈ 210 ps.
- Detected single Mn2+ ions in quantum dots.

## Abstract

This work presents epitaxial growth and optical spectroscopy of CdTe quantum dots (QDs) in (Cd,Zn,Mg)Te barriers placed on the top of (Cd,Zn,Mg)Te distributed Bragg reflector. The formed photonic mode in our half-cavity structure permits to enhance the local excitation intensity and extraction efficiency of the QD photoluminescence, while suppressing the reflectance within the spectral range covering the QD transitions. This allows to perform coherent, nonlinear, resonant spectroscopy of individual QDs. The coherence dynamics of a charged exciton is measured via four-wave mixing, with the estimated dephasing time $T_2=(210\,\pm\,40)$ ps. The same structure contains QDs doped with single Mn$^{2+}$ ions, as detected in photoluminescence spectra. Our work therefore paves the way toward investigating and controlling an exciton coherence coupled, via $s$,$p$-$d$ exchange interaction, with an individual spin of a magnetic dopant.