title: Nuclear state preparation via Landau-Zener-Stückelberg transitions in double quantum dots.
abstract: We theoretically model a nuclear-state preparation scheme that increases the coherence time of a two-spin qubit in a double quantum dot. The two-electron system is tuned repeatedly across a singlet-triplet level anticrossing with alternating slow and rapid sweeps of an external bias voltage. Using a Landau-Zener-Stückelberg model, we find that in addition to a small nuclear polarization that weakly affects the electron spin coherence, the slow sweeps are only partially adiabatic and lead to a weak nuclear spin measurement and a nuclear-state narrowing which prolongs the electron spin coherence. This resolves some open problems brought up by a recent experiment [D. J. Reilly, Science 321, 817 (2008).10.1126/science.1159221]. Based on our description of the weak measurement, we simulate a system with up to n=200 nuclear spins per dot. Scaling in n indicates a stronger effect for larger n.
authors.affiliation: Department of Physics, University of Konstanz, D-78457 Konstanz, Germany.
authors.forename: Hugo
authors.initials: H
authors.lastname: Ribeiro
authors.forename: Guido
authors.initials: G
authors.lastname: Burkard