  We use fast coherent reflectivity measurements, in a strongly-coupled quantum
dot-micropillar device, to monitor in real-time single-charge jumps at the
microsecond timescale. Thanks to the strong enhancement of light-matter
interaction inside the cavity, the measurement rate is five orders of magnitude
faster than with previous experiments of direct single-charge sensing with
quantum dots. The monitored transitions, identified at any given time with a
less than 0.2% error probability, correspond to a carrier being captured and
then released by a single material defect. This high-speed technique opens the
way for the real-time monitoring of other rapid single quantum events, such as
the quantum jumps of a single spin.
