Direct measurement of hyperfine shifts and radiofrequency manipulation of the nuclear spins in individual CdTe/ZnTe quantum dots

We achieve direct detection of electron hyperfine shifts in individual CdTe/ZnTe quantum dots. For the previously inaccessible regime of strong magnetic fields $B_z\gtrsim0.1$ T, we demonstrate robust polarization of a few-hundred-particle nuclear spin bath, with optical initialization time of $\sim$ 1 ms and polarization lifetime exceeding $\sim$ 1 s. Nuclear magnetic resonance spectroscopy of individual dots reveals strong electron-nuclear interactions characterized by the Knight fields $|B_e|\gtrsim50$ mT, an order of magnitude stronger than in III-V semiconductor quantum dots. Our studies confirm II-VI semiconductor quantum dots as a promising platform for hybrid electron-nuclear spin quantum registers, combining the excellent optical properties comparable to III-V dots, and the dilute nuclear spin environment similar to group-IV semiconductors.