Nuclear spin quantum memories in quantum dots revealed by nuclear magnetic resonance

Optical pumping is known as a most efficient tool to achieve a high value of nuclear spin polarization. In negatively charged QDs containing, in average, a single resident electron, the angular momentum of a photon is transferred to the electron spin thanks to non-zero spin-orbit coupling in III-V semiconductor. Due to a strong localization, the electron spin is rapidly relaxes via hyperfine interaction with nuclei. In spite of this fast relaxation, the long electron-nuclear correlation time allows one to monitor the nuclear spin system state via electron-spin polarization dynamics. Combining the optical pumping and optical detection with some advances of NMR, we come up with optically detected NMR (ODNMR), which very recently has become a very promising tool for studying nuclear spin dynamics in single QDs and QD ensembles. Here, a brief review of recent studies in the QD ensembles will be presented.