We theoretically demonstrate that nuclear spins can be harnessed to coherently control two-electron spin states in a double quantum dot. Hyperfine interactions lead to an avoided crossing between the spin singlet state and the ms = +1 triplet state, T_+ . We show that a coherent superposition of singlet and triplet states can be achieved using finite-time Landau-Zener-St\"uckelberg interferometry. In this system the coherent rotation rate is set by the Zeeman energy, resulting in ~1 nanosecond single spin rotations. We analyze the coherence of this spin qubit by considering the coupling to the nuclear spin bath and show that T_2^* ~ 16 ns, in good agreement with experimental data. Our analysis further demonstrates that efficient single qubit and two qubit control can be achieved using Landau-Zener-St\"uckelberg interferometry.
@article{arxiv.1002.4630,
title = {Harnessing the GaAs quantum dot nuclear spin bath for quantum control},
author = {Hugo Ribeiro and J. R. Petta and Guido Burkard},
journal= {arXiv preprint arXiv:1002.4630},
year = {2011}
}