Vanishing electron g factor and long-lived nuclear spin polarization in weakly strained nanohole-filled GaAs/AlGaAs quantum dots

GaAs/AlGaAs quantum dots grown by in situ droplet etching and nanohole in-filling offer a combination of strong charge confinement, optical efficiency, and high spatial symmetry advantageous for polarization entanglement and spin-photon interface. Here, we study experimentally electron and nuclear spin properties of such dots. We find nearly vanishing electron $g$ factors $({g}_{e}l0.05)$, providing a potential route for electrically driven spin control schemes. Optical manipulation of the nuclear spin environment is demonstrated with nuclear spin polarization up to $65%$ achieved. Nuclear magnetic resonance spectroscopy reveals two distinct types of quantum dots: with tensile and with compressive strain along the growth axis. In both types of dots, the magnitude of strain ${\ensuremath{\epsilon}}_{b}l0.02%$ is nearly three orders of magnitude smaller than in self-assembled dots: On the one hand, this provides a route for eliminating a major source of electron spin decoherence arising from nuclear quadrupolar interactions, and on the other hand such strain is sufficient to suppress nuclear spin diffusion leading to a stable nuclear spin bath with nuclear spin lifetimes exceeding 500 s. The spin properties revealed in this work make this new type of quantum dot an attractive alternative to self-assembled dots for the applications in quantum information technologies.