  Single-shot measurement of the charge arrangement and spin state of a double
quantum dot are reported, with measurement times down to ~ 100 ns. Sensing uses
radio-frequency reflectometry of a proximal quantum dot in the Coulomb blockade
regime. The sensor quantum dot is up to 30 times more sensitive than a
comparable quantum point contact sensor, and yields three times greater signal
to noise in rf single-shot measurements. Numerical modeling is qualitatively
consistent with experiment and shows that the improved sensitivity of the
sensor quantum dot results from reduced screening and lifetime broadening.
