Harnessing the GaAs quantum dot nuclear spin bath for quantum control

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-Stückelberg interferometry. In this system the coherent rotation rate is set by the Zeeman energy, resulting in 1 ns single spin rotations. We analyze the coherence of this spin qubit by considering the coupling to the nuclear spin bath and show that T2 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-Stückelberg interferometry.