Radio frequency charge sensing and nuclear polarization of a two-electron double quantum dot*

We report charge-sensing measurements of a two-electron double quantum dot using an electrometer based on a radio-frequency quantum point contact (rf-QPC). In analogy with the radio frequency single electron transistor (rf-SET) the rf-QPC makes use of a LC impedance transformer and radio frequency reflectometry to achieve high charge sensitivity over a bandwidth exceeding 20MHz. In addition, we use controlled nanosecond pulsing of the double-dot potential to drive singlet to triplet transitions that develop a partial polarization of the nuclear spins. Using the rf-QPC, the subsequent diffusion and dynamics of nuclear polarization is examined on fast timescales.