Abstract

Advances in our ability to control electron spins in a double quantum dot allow for the experimental manipulation of a mesoscopic ensemble of nuclear spins. As interaction of these nuclear spins with other degrees of freedom are extremely weak, such control can be used to drive nuclear spins far out of equilibrium. At the simplest level, nuclear spins can be efficiently polarized, and I will describe theoretical and experimental advances in our understanding of this effect. More curiously, I will also report on a natural feedback mechanism that leads to the formation of stable “dark” configurations of nuclear spins. These dark states no longer interact strongly with the electron spin and dramatically reduce the inhomogeneous broadening in the system, resulting in an increase in $T_2^*$ from 20 to 900 nanoseconds.