Antireflective Photonic Structure for Coherent Nonlinear Spectroscopy of Single Magnetic Quantum Dots

This work presents epitaxial growth and optical spectroscopy of CdTe quantum dots (QDs) in (Cd,Zn,Mg)Te barriers placed on top of the (Cd,Zn,Mg)Te distributed Bragg reflector. The photonic mode formed in our halfcavity structure permits enhancement of the local excitation intensity and extraction efficiency of the QD emission, while suppressing the reflectance within the spectral range covering the QD transitions. This allows us 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 T2 = (210 ± 40) ps. The same structure contains QDs doped with single Mn2+ ions, as detected in photoluminescence spectra. Our work therefore paves the way toward investigating and controlling coherence of individual excitons coupled, via s,p-d exchange interaction, with individual spins of magnetic dopants.