  Nanostructures defined in high-mobility two-dimensional electron systems
offer a unique way of controlling the microscopic details of the investigated
device. Quantum point contacts play a key role in these investigations, since
they are not only a research topic themselves, but turn out to serve as
convenient and powerful detectors for their electrostatic environment. We
investigate how the sensitivity of charge detectors can be further improved by
reducing screening, increasing the capacitive coupling between charge and
detector and by tuning the quantum point contacts' confinement potential into
the shape of a localized state. We demonstrate the benefits of utilizing a
localized state by performing fast and well-resolved charge detection of a
large quantum dot in the quantum Hall regime.
